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A = ελbC

Beers law is mathematically defined as:

partition coefficient

For the first part of this experiment (Day 1), one of the goals is to determine the _____________ by extracting ethanol from a 1 mL sample of 5% ethanol solution with 1 mL of pentanol.

For a solute (S) partitioning between aqueous and organic solvents you can write K = _______. A. ([S]organic/[S]aqueous) x q^n B. ([S]aqueous/[S]organic) x q^n C.[S]organic/[S]aqueous D. ([S]organic/[S]aqueous)^n E. [S]aqueous/[S]organic F. ([S]aqueous/[S]organic)^n

C.[S]organic/[S]aqueous

8.20 x 103 M-1 cm-1

using structures for all species, write the complete esterification reaction begun below: methanol (CH3OH) + salicylic acid ------H2SO4------> ?

H3c-o::-H + []-OH =O-OH + H2O

Glucose oxidase catalyzes the reaction of ___________ with O2?

Glucose

Titration end point

when there is a color change then the end point has been reached

2. Would the molar mass of a volatile liquid, calculated using the procedure in this experiment, be incorrectly high, incorrectly low, or unaffected by the following procedural changes?

(a) You did not completely vaporize the liquid when you heated it. When not completely vaporized then pressure value was less than actual. As a result, the value of n would be less. Molar mass value would be incorrectly high. (b) The foil cap got wet while you were cooling the flask and its contents with running water. When the foil cap retained some water, increasing the vapor pressure value.making the, value of n would increase and consequently the molar mass value would be incorrectly low. (c) You added the boiling stone to the flask after you had already determined the mass of the empty flask and foil cap. then stones mass was added to the mass of the unknown liquid. As a result, the molar mass value was incorrectly high. (d) You forgot to measure the volume of the flask, so you used the volume printed on the flask for your calculations. Volume measured from the volume printed on the flask was correct and the value of molar mass was unaffected. (e) Your unknown liquid had a boiling point of 102.3 Celsius. If the unknown liquid had a boiling point higher than water then they would never boil a result, pressure value would be low and the molar mass value would be incorrectly high

(to contain) graduated cylinder = to hold a specified amount of volume Ex. volumetric flask

The accepted ΔH neutzn of hydrobromic acid(HBr) reactingwith NaOH solution and HNO3 reacting with potasium hydroxide (KOH)solution are identical. 1. Write net ionic equations to show whataqueous HBr and HNO3 have in common.

H+(aq) + Br- (aq) + Na+(aq) +OH-(aq) ----------> Na+(aq) +Br-(aq) + H2O(l) H+ (aq) +NO3- (aq) + K+(aq) +OH-(aq) ----------> K+(aq) +NO3-(aq) +H2O(l) Net ionic equations H+ (aq) +OH-(aq)----------> H2O(l) H+ (aq) +OH-(aq)----------> H2O(l)

Does diluting a buffer solution with pure water alter the ph of the solution? Why or why not?

The change in pH is insignificant It does not have a huge change in moles of hydronium or OH ions So the ratio of moles is relatively the same and the pH will not change

What commercial samples will you analyze today in ethanol in beer experiment?

Non-Alcoholic Beer, Regular Beer, Light Beer

Why does bromothymol blue change color when the pH shifts from acidic to basic? A. The atoms move with in the molecule. B. Upon the loss of a proton, there is a structural rearrangement within the molecule that changes the electronic structure of the molecule. C. There is an increase in the concentration of the bromothymol blue as the irreversible reaction proceeds to completion. D. There is a change in the equilibrium constant of the acidic and basic forms.

You add 1.00 x 102 mL of 0.10 M NaOH to 1.00 x 102 mL of 0.50 M Formic acid (HCOOH; pKa = 3.744). What is the pH of this solution? A. 4.35 B. 3.14 C. 3.744 D. 2.79

You wish to prepare a buffer with a pH of 7.10. Which of the below combinations would be best to prepare this buffer? A. CH3CO2H and CH3CO2- (pKa = 4.74) B. H2CO3 and HCO3- (pKa = 6.38) C. H3PO4 and H2PO4- (pKa = 2.12) D. HCOOH and HCOO- (pKa = 3.74)

___________________ is defined any analytical method that relies on measuring the mass of a substance to complete the analysis. A. Volumetric analysis B. Gravimetric analysis C. Background correction D. Calibration

Which of the following enzyme(s) will you use in today's lab? (select all that apply) A. galactosidase B. Glucose oxidase C. Horseradish peroxidase D. Lactase E. Catalase

What commercial samples will you analyze today? (select all that apply) A. Wine B. Regular Beer C. Non-Alcoholic Beer D. Nyquil E. Listerine F. Light Beer

bcf

This value does need to be corrected. To determine the correction factor, find the equation of the line that connects the two points you measured, and use this line to determine the correction factor for you measurement. Then, apply this correction factor.

You created the calibration curve above for a "To Contain" graduated cylinder. Using this same graduated cylinder, you measured 43.76 mL and now want to use the graph above to do so. The two data points that this value falls in between are (40.00 mL, 0.082 mL) and (50.00 mL, -0.030 mL). What would the CORRECTED volume measurement be?

To determine the pKa of the bromothymol blue, you will construct a plot of ______

dAbsorbance/dpH vs. Average pH First Derivative Plot

Unlike glucose or fructose, sucrose is a

disaccharide

In a Bradford assay, you will measure the UV/visible absorption changes of a protein (dye or protein) as they bind to (bind to or separate from) each other.

dye/bind to

In a Bradford assay, you will measure the UV/visible absorption changes of a _______________(dye or protein) as they ___________(bind to or separate from) each other.

dylestain, bind to

To determine the pKa of the bromothymol blue, you will construct a plot of _____________. A. Absorbance vs. Wavelength B. Wavelength vs. Absorbance C. dAbsorbance/dpH vs. pH D. dpH/dAbsorbance vs. pH E. dAbsorbance/dpH vs. Average pH F. dpH/dAbsorbance vs. Average pH

54.20 mL

You created the calibration curve above for a "To Contain" graduated cylinder. Using this same graduated cylinder, you measured 54.25 mL and now want to use the graph above to do so. The two data points that this value falls in between are (50.00 mL, -0.030 mL) and (60.00 mL, -0.076 mL). What would the CORRECTED volume measurement be?

(e) What is the cost per oz of acetic acid?

(3.3/5.36)x100 =61.567 =62

(d) if 16 oz of the vinagar cost 53 cents, what is the cost per oz of vinagar solution?

(53/16)=3.31 cents oz

Coupled reaction

2 reactions to overall get what we are looking for

how many times were the sugar solutions diluted?

25x

what is the minimum recommended amount of points required for a pH calibration curve?

Which of the below is the correct Henderson-Hesselbalch equation? A. pKa = pH + Log [A-]/[HA] B. pH = pKa + Log [A-]/[HA] C. pH = pKa + Log [HA]/[A-] D. pKa = pH - Log [HA]/[A-]

B. pH = pKa + Log [A-]/[HA]

You add 100 mL of 0.10 M NaOH to 100 mL of 0.50 M Formic acid (HCOOH; pKa = 3.744). What is the pH of this solution? pH =

3.14|3.1|3.142 Remember to use the Henderson-Hasselbalch equation. Also, the strong acid will convert the weak base to the weak acid and this must be accounted for.

You add 100 mL of 0.20 M HCl to 100 mL of 0.50 M formate (HCOO-). What is the pH of this solution? (For HCOOH the pKa is 3.744).

3.9

54.20 mL

On the basis of an accepted Delta H_neutzn of 58.5 kJ mol^-1 for the reaction, determine the percent error in your calculated Delta H-neutzn.

58.5-56 -------- x 100 = 4.3% 58.5

You wish to prepare a buffer with a pH of 4.00. Which of the below combinations would be best to prepare this buffer? A. HCOOH and HCOO- (pKa = 3.74) B. H2CO3 and HCO3- (pKa = 6.38) C. H3PO4 and H2PO4- (pKa = 2.12) D. CH3CO2H and CH3CO2- (pKa = 4.74)

A HCOOH and HCOO- (pKa = 3.74)

Which of the below conditions will be investigated today? (select all that apply) A. Varying the reaction time B. Varying the amount of enzyme mix added. C. Varying the amount of Glucose oxidase added. D. Varying the amount of ferrocyanide solution added. E. Varying the reaction temperature conditions

A, B, E In this lab we will investigate the effect of the volume of enzyme mix (not just glucose oxidase), reaction temperature, and reaction time.

Which of the following enzyme(s) will you use in today's lab? (select all that apply) A. Glucose oxidase B. Catalase C. galactosidase D. Horseradish peroxidase E. Lactase

A, D Feedback: Partially correct; please check the lab manual for the other enzyme being used today. ???

A. 43.80 mL

Which one of these is not a buffer? A. The partial dissociation of a weak acid in solution B. A solution of weak base to which strong acid is added such that the concentration of strong acid is less than the concentration of weak base C. A solution of weak acid to which strong base is added such that the concentration of strong base is less than the concentration of weak acid D. A solution of weak acid to which its conjugate base is added

A. The partial dissociation of a weak acid in solution

By which method should you calibrate a 50-mL burette?

A. To Dispense

What is the primary goal of the second part of the experiment (Day 2)? A. To determine the percent alcohol (ethanol) in beer (alcoholic and non-alcoholic). B. To collect data regarding percent ethanol in standard samples. C. To extract ethanol from beer samples. D. To determine the amount of alcohol in a known sample

A. To determine the percent alcohol (ethanol) in beer (alcoholic and non-alcoholic).

Molar absorptivity provides information about: A. how much light a molecule absorbs at a particular wavelength. B. how much a molecule absorbs at all visible wavelengths. C. the concentration of a molecule within a sample D. the amount of sample that interacts with light at a particular wavelength.

A. how much light a molecule absorbs at a particular wavelength.

In the glucose experiment you will construct a plot of

Absorbance vs. Concentration

why add salt to the pentanol in ethanol standards?

Add salt to saturate the aqueous layer to push as much ethanol out of the water and into the pentanol layer as we can

What precautions should be taken when using separatory funnel for your extraction?

Aim the end of the funnel toward the back of your hood. Vent to release pressure immediately after adding solvents together.

In today's lab you will determine the amount of glucose in which of the following samples?

An undigested sugar solution An acid-digested sugar solution Gatorade

In order to make an acetic acid/sodium acetate buffer of pH 5.76, you would use sodium acetate with which of the following (select all that apply): A. H2SO4 B. acetic acid C. HCl D. NaCl E. NaOH

B. acetic acid C. HCl Remember, you can prepare the buffer by the theoretical means (conjugate acid/base pair) or by the theoretical means (weak base, add strong acid to generate conjugate acid).

Which of the below is the correct Henderson-Hesselbalch equation? A. pH = pKa + Log [HA]/[A-] B. pH = pKa + Log [A-]/[HA] C. pKa = pH + Log [A-]/[HA] D. pKa = pH - Log [HA]/[A-]

B. pH = pKa + Log [A-]/[HA]

Mathematically buffer capacity is defined as: A. none of these are correct B. β = - dCacid / dpH = dCbase / dpH C. β = dCacid / dpOH = - (dCbase / dpH) D. β = dCacid / dpH = dpH / dCbase

B. β = - dCacid / dpH = dCbase / dpH

Briefly explain why the procedure you used to determine boiling point would not work for liquids with boiling point greater than 100 degrees C.

Because it is sitting in water and the boiling point for water is 100 degrees so the water tempurature cannot get any higher.

If a piece of glassware breaks during your experiment, the first thing you should do is: A. Go to Morehead 102 and purchase your replacement glassware. B. Sweep up the broken pieces and dispose of them in the glass waste box. C. Inform the TA and ask for assistance. D. Pick up the broken pieces of glass and dispose of the in the glass waste box.

C. Inform the TA and ask for assistance.

In Experiment 5, why do you need to add NaCl during the extraction of the spinach pigments? A. The NaCl breaks down the spinach to allow for extraction of the pigments. B. The extraction would be the same whether or not NaCl were added. C. The NaCl helps to drive the more polar pigments into the organic layer. D. The NaCl helps to drive the less polar pigments into the organic layer

C. The NaCl helps to drive the more polar pigments into the organic layer.

Compound X is known to absorb at 510 nm. If you dilute a solution containing Compound X by 1/3, how does the absorbance change? The same cuvet is used for all measurements. A. It is not affected by the dilution. B. The absorbance triples. C. The absorbance decreases by 1/3 its original value. D. The absorbance increases by 103.

C. The absorbance decreases by 1/3 its original value.

For the first part of this experiment (Day 1), one of the goals is to determine the _____________ by extracting ethanol from a 1 mL sample of 5% ethanol solution with 1 mL of pentanol. A. solubility constant B. Percent ethanol in beer C. partition coefficient D. location of the organic layer

C. partition coefficient

Mathematically buffer capacity is defined as: A. β = dCacid / dpH = dpH / dCbase B. none of these are correct C. β = - dCacid / dpH = dCbase / dpH D. β = dCacid / dpOH = - (dCbase / dpH)

C. β = - dCacid / dpH = dCbase / dpH

1.64 x 104 M-1 cm-1

Calculate the molar absorptivity of bromothymol blue at 620 nm if the percent transmittance (% T) is determined to be 15.1% at this wavelength. The pathlength of the cuvet is 10.0 mm and the concentration of bromothymol blue solution is 5.00 x 10-5 M.

0.33 If 1/4 (or 25%) of the analyte goes into the organic phase, then 3/4 (or 75%) of it remains in the aqueous phase. Since K= [A]org/[A]aq, here K=0.25/0.75.

Calculate the partition coefficient if 1/4 of a 10% ethanol sample is extracted from the aqueous phase with 1-pentanol. (Hint: K = [CH3CH2OH]org / [CH3CH2OH]aq)

Calculate the molar absorptivity of bromothymol blue at 620 nm if the measured absorbance at this wavelength is 0.410, the pathlength is 10.0 mm and the concentration of bromothymol blue is 5.0 x 10-5 M. A. 1.64 x 103 M-1 cm-1 B. 4.1 x 10-5 M-1 cm-1 C. 1.64 x 105 M-1 cm-1 D. 8.20 x 103 M-1 cm-1

D. 8.20 x 103 M-1 cm-1

What are some applications of gas chromatography? A. determine amount of the analyte in a mixture B. test the purity of the analyte C. to isolate pure compounds from a small amount of a mixture D. All of the above E. A and B F. A and C G. B and C

D. All of the above

Which of the following are true at the inflection point of the absorbance vs. pH plot? A. [HIn] = [In-] B. The isoelectric point (pH) has been reached. C. pH = pKa D. Both A and C

D. Both A and C

What indicator molecule are we using in today's experiment? A. Bromocresol blue B. Hemoglobin C. Dextran blue D. Bromothymol blue

D. Bromothymol blue

The rate of a molecule's movement in an electric field is a function of all of the following EXCEPT: A. Molecular shape B. Average net charge C. Molecular size D. Concentration

D. Concentration

For both types of calibration curves you will make this week, which of the following plots to achieve the goal of the experiment? A. Retention Time vs Ethanol Peak Area B. Retention Time vs Percentage of Ethanol C. 1-Pentanol Peak Area vs Percent of Ethanol D. Ethanol Peak Area vs Percent of Ethanol

D. Ethanol Peak Area vs Percent of Ethanol

the same student mixed the crystalline product with ethanolic 1% FeCl3 solution and obtained a colored solution. briefly explain what might have caused this result.

FeCl3 is used to indicate the presence of a phenol by turning purple color. the color change was a result of still having salicylic acid a result of improper heating.

In the presence of horseradish peroxidase and H2O2, _____________ is oxidized.

Ferrocyanide

In the presence of horseradish peroxidase and H2O2, _____________ is oxidized. A. Both ferricyanide and and ferrocyanide B. Ferricyanide C. Ferrocyanide D. D-Glucolactone

Ferrocyanide is oxidized by horseradish peroxidase (Remember Ferro vs Ferricyanide (Ferro is the compound oxidized)).

Separatory Funnel

For LC, which of the below pieces of glassware will you use to perform the solvent-solvent extraction.

[S]organic/[S]aqueous

For a solute (S) partitioning between aqueous and organic solvents you can write K = _______.

Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be.

In this experiment you are trying to determine _____________. A. the wavelength at which the acidic and basic forms of bromothymol blue absorb maximally. B. the partition coefficient of bromothymol blue in a water-ethyl acetate mixture. C. the pKa of bromothymol blue D. A, B, and C E. B and C F. A and B G. A and C

G. A and C

Gas chromatography (GC), can be used for which of the following A. to determine the purity of a substance. B. to separate the components of mixtures. C. to quantitate realtive amounts of the components in a mixture. D. to qualitatively identify compounds in a mixture. E. A, B, and C F. A, B and D G. A, B, C and D

G. A, B, C and D

Which of the following enzyme(s) will you use in today's lab? (select all that apply)

Glucose oxidase Horseradish peroxidase

Glucose

Glucose oxidase catalyzes the reaction of ___________ with O2?

___________________ is defined any analytical method that relies on measuring the mass of a substance to complete the analysis.

Gravimetric analysis

What are the main classes of pigments found in plants, like the spinach you will use today. A. Porphyrins B. Phycobilins C. Flavenoids D. Carotenoids E. Melanin F. All of the above G. A, B and C H. A, C and D I. B, C and E

H. A, C and D

How d we calculate pKa f bromothymol blue

Inflection point on the absorbance vs. pH plot or the peak on the dAbs/dpH vs average pH plot

If a piece of glassware breaks during your experiment, the first thing you should do is:

Inform the TA and ask for assistance.

HA and A- in solution produces what when adding a strong base

Initially you produce more A- than excess free OH- causing less drastic pH change

What are the goals and objectives for Experiment 2: Affinity Chromatography?

Purify E. coli lysate using affinity chromatography. Determine the molecular weight of the protein using SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Quantify the amount of protein in our purified lysate using a Bradford assay.

Calibrate with pH electrode

Use 2 or 3 points of a known pH solution pH is measured on the Glass membrane part of the electrode Ion selective electrode Monitors the hydrogen ion concentration Potential difference translated to pH

A. resolution C. relative retention

Two common parameters that are often used to describe the efficiency of a separation are ______ and _____.

Use formic acid and 0.1 M NaOH to prepare your buffer.

1.) Briefly describe the safety precautions that you must take working with flammable compounds.

Wear eye protection handle with care, no open flames

A. Determine the molecular weight of the protein using SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). B. Purify E. coli lysate using affinity chromatography. C. Quantify the amount of protein in our purified lysate using a Bradford assay.

What are the goals and objectives for Experiment 2: Affinity Chromatography? (Select all that apply.)

Bromothymol blue

What indicator molecule are we using in today's experiment?

± 1

What is the acceptable range of pKas that you can use to make a buffer of a certain pH?

It increases the precision of our measurements and ensures that the results are repeatable. While the act of repeating many calibration trials may allow us to more precisely know the quantity we are measuring, the act of calibration is not designed to lend more precision to our results. Instead, it is designed to give us more confidence that the value we measure is closer to the true value of the quantity of interest.

What of the following is NOT a reason for which the calibration of laboratory glassware important?

D. It increases the precision of our measurements and ensures that the results are repeatable.

What of the following is NOT a reason for which the calibration of laboratory glassware important? A. The calibration of glassware and equipment ensures that the answers we arrive at after the experiment is complete is a better reflection of the true answer. B. It increases the accuracy of our measurements so that our measurement lies closer to the true value of the quantity of interest. Feedback: This reason above is one reason we calibrate equipment. C. It provides us with information about how our specific glassware measures the quantity in question as opposed to what the manufacturer claims it can do. D. It increases the precision of our measurements and ensures that the results are repeatable.

A. Vent to release pressure immediately after adding solvents together. C. Aim the end of the funnel toward the back of your hood.

What precautions should be taken when using separatory funnel for your extraction?

goal of bromothymol blue experiment

Where is the acidic vs. basic form are during the ethyl acetate and water extraction Determine the pka of bromothymol blue Calculate molar absorptivity

3 only there must be both the conjugate acid and base present after mixing has occurred.

Which combination(s) of equal volumes of the below reactants would result in the formation of a buffer? 1. 0.10 M CH3COOH and 0.05 M CH3COO- 2. 0.10 M CH3COOH and 1.0 M NaOH 3. 0.10 M CH3COO- and 0.10 M HCl

pH = pKa + Log [A-]/[HA]

Which of the below is the correct Henderson-Hesselbalch equation?

B. The isoelectric point (pH) has been reached. C. pH = pKa

Which of the following are true at the inflection point of the absorbance vs. pH plot?

Glucose oxidase ; Horseradish peroxidase

Which of the following enzyme(s) will you use in today's lab? (select all that apply)

Ka = 6.32 x 10-2

Which of the following values indicate the strongest acid?

Upon the loss of a proton, there is a structural rearrangement within the molecule that changes the electronic structure of the molecule.

Why does bromothymol blue change color when the pH shifts from acidic to basic?

Your flow rate is very high when you ran your GC. Is this bad?

Yes, this will increase plate height and resolution will decrease.

3.14

You add 1.00 x 102 mL of 0.10 M NaOH to 1.00 x 102 mL of 0.50 M Formic acid (HCOOH; pKa = 3.744). What is the pH of this solution?

2.750

You add 100 mL of 0.10 M HCl to 100 mL of 0.50 M phosphate (H2PO4-; pKa = 2.148). What is the pH of this solution?

61.41 mL you cannot simply average the two correction factors on either side. To determine the correction factor, find the equation of the line that connects the two points you measured, and use this line to determine the correction factor for you measurement. Then, apply this correction factor.

You created the calibration curve above for a "To Contain" graduated cylinder. Using this same graduated cylinder, you measured 61.50 mL and now want to use the graph above to do so. The two data points that this value falls in between are (60.00 mL, -0.076 mL) and (70.00 mL, -0.141 mL). What would the CORRECTED volume measurement be?

Use formic acid and 0.1 M NaOH to prepare your buffer.

1 mL diluted to 25 mL

You have a solution that you wish to dilute 25 times (25x). Which of the below represents a 25x dilution?

2.5 M

You take 10.0 mL of your unknown solution and dilute it to 100. mL. You then determine that the concentration of this diluted sample is 0.25 M. What was the concentration of the original (undiluted) sample?

CH3CO2H and CH3CO2- (pKa = 4.74)

You wish to prepare a buffer with a pH of 5.25. Which of the below combinations would be best to prepare this buffer?

H2CO3 and HCO3- (pKa = 6.38)

You wish to prepare a buffer with a pH of 7.10. Which of the below combinations would be best to prepare this buffer?

What do we need to determine the concentration of each form of bromothymol blue in solution?

You would need the absorbance of that species at the wavelength of maximum absorbance, molar absorptivity at the wavelength of maximum absorbance, and the path length Absorbance of the acidic + Absorbance of the basic = total absorbance The isosbestic point. We can use molar absorptivity at this point because both species has the same molar absorptivity

By which method would you calibrate a 100-mL volumetric flask? A. To Contain B. To Dispense

Which of the following statement(s) describe(s) buffer solutions? (select all that apply) A. The pKa value(s) of the reagents selected and desired buffer pH, must be within +/- 1 pH unit of each other in order to prepare a proper buffer solution. B. The weak base portion can consume strong acid to help resist pH changes C. The weak acid component can consume strong base to help resist pH changes D. They are capabale of resisting changes in pH E. The weak acid portion can consume strong acid to help resist pH changes

abcd

why was acetonitrile added to the organic layer of the spinach extract?

acetonitrile was used to increase the polarity of the organic layer

You determine that you need to use formic acid to prepare your buffer solution, but you discover when you arrive to lab that the conjugate base of formic acid (sodium formate) is not available. What should you do? A. Let your TA know so that they can call down to the prep staff to have some sodium formate brought up to lab. B. Let your TA know that you will need a new pH value because there is no conjugate base available. C. Use formic acid and 0.1 M NaOH to prepare your buffer. D. Use formic acid and 0.1 M HCl to prepare your buffer solution.

You have a solution that you wish to dilute 50 times (50x). Which of the below represents a 50x dilution? A. 25 mL of a solution diluted to 100 mL B. 50 mL of the solution diluted to 1.0 mL C. 1.0 mL of a solution diluted to 50.0 mL D. 25 mL of a solution diluted to 50 mL

divide by 1000mL

In a Bradford assay, you will measure the UV/visible absorption changes of a (dye or protein) as they (bind to or separate from) each other.

dye, bind to

at what point in the titration is the pH of the solution equal to the pKa of the indicator?

equivalence point

Which combination(s) of equal volumes of the below reactants would result in the formation of a buffer? 1. 0.1 M CH3COOH and 0.05 M CH3COO- 2. 0.1 M CH3COOH and 0.05 M NaOH 3. 0.1 M CH3COO- and 0.05 M HCl A. 1 only B. 2 only C. 3 only D. 1 and 2 only E. 1 and 3 only F. 1, 2, and 3

You will use the partition coefficient determined in Day 1 to help calculate the percent ethanol in the beer samples in Day 2? True false

false

what are we measuring at 420 nm?

ferricyanide

What are some common reasons to carry out an extraction? A. isolate the desired analyte B. concentrate the desired analyte C. to modify the desired analyte D. separate the analyte to avoid interference with other species E. All of the above F. A, B & C G. A, B & D H. A, C & D

what is dextrose

glucose

what is oxidized by GOx?

glucose

what is dextrose?

glucose (a monosaccharide)

carrier gas

helium

what characteristic of proteins does affinity chromatography take advantage of?

high affinity for the solid phase

What does a partition coefficient >1 indicate?

higher affinity for organic phase

Molar absorptivity provides information about:

how much light a molecule absorbs at a particular wavelength.

theoretical method

selecting 2 reagents with a pKa based on the assigned pH use the HH equation to calculate the amount of each reagent needed add to volumetric flask and dilute to the line

What is table sugar?

sucrose

what type of error does calibration minimize?

systematic error

should [glucose] calculated be higher, lower, or the same as [sugar] reported on the bottle?

lower

The titration of 25.00 mL of a vinegar sample with 0.500 N sodium hydroxide solution required 44.60 mL . Assume the density of the vinegar sample is 1.00g mL b) Calculate the number of grams of acetic acid in the sample.

mass of acitic acid 60 grams 0.0223 x 60/1 = 1.338

in a reverse-phase LC experiment, the stationary phase is (polar/non-polar) and the mobile phase is (polar/non-polar).

non polar, polar

A pressed polystyrene top was used to cover the polystyrene cup after the acid and the base solutions had been mixed how it would afect the resuts

nothing as long as the reactants and solvents were ionic

which layer is on top?

organic

Which of the below is the correct Henderson-Hesselbalch equation?

pH = pKa + Log [A-]/[HA]

what is the purpose of centrifuging cells?

removing insoluble proteins and lysing the cells

In experiment 5, you will perform a (reverse/normal) phase LC experiment using a (isocratic/step-gradient) elution procedure.

reverse, step gradient

why were we not able to quantify the concentrations of the spinach pigments in our extraction?

we don't know the molar absorptivities

steps to calibrate a TC

weigh flask without water, measure out set volume of water and reweigh the flask. With density determine the volume from difference in mass

If a standard addition plot was constructed for a given analysis and the linear regression gave you a slope of 1.5 and a y-intercept of 4, what is the percentage of ethanol in the sample?

x intercept (absolute value) 2.67%

To Dispense

By which method should you calibrate a 5-mL micropipette?

Does it matter if its wet before hand for the TD

It doesn't matter because the water will be counted in the measured volume listed so it will dispense the same amount

Why GC?

Our solvents and ethanol have high volatility and low bp

Absorbance =

log I0/I or -log(T)

(t dispense) graduated cylinder = to dispense a specific volume Ex. Syringe, volumetric and graduated pipettes

You add 100 mL of 0.10 M HCl to 100 mL of 0.70 M phosphate (H2PO4-; pKa = 2.148). What is the pH of this solution? pH =

2.93

Which is the weakest acid based on pKa? A. Ka = 6.05 x 10^-10 B. Ka = 1.03 x 10^-2 C. Ka = 5.73 x 10^-7 D. Ka = 3.95 x 10^-5

A. Ka = 6.05 x 10^-10

The type of plot you will construct in Day 2 of this experiment is called a ____________. (exp 1) A. Standard Addition Plot B. Standard Calibration Plot C. Derivative Plot D. Internal Standard Plot

A. Standard Addition Plot

___________ is defined as the process of relating the actual physical quantity (such as volume) to the quantity indicated on the scale of an instrument.

Calibration

dilution equation

M1V1=M2V2

Explain how the following changes in the procedure for this experiment would affect the results. A) A glass beaker was used instead of a pressed polystyrene cup?

-It insulates causing a more accurate measurement B)

Which of the following are true at the inflection point of the absorbance vs. pH plot? A. [HIn] = [In-] B. The isoelectric point (pH) has been reached. C. pH = pKa D. Both A and C

. Both A and C

Recalculate your percent yield, taking into account the water solubility of aspirin when you calculate the theoretical yield.

0.0152 x 180/1mol = 2.74 g

The titration of 25.00 mL of a vinegar sample with 0.500 N sodium hydroxide solution required 44.60 mL . Assume the density of the vinegar sample is 1.00g mL a) Calculate the number of gram-equivalents of acetic acid in the vinegar sample.

0.0223 x 1/1 = 0.223 g

Calculate the number of moles of HNO_3 reacting when 50.0 mL of 3.00 M HNO_3 and 50.5f 1.00 M NaOH solution are mixed.

0.05 x 1 = 0.05

How many grams of aspirin were lost in the washing process you used to purify your product, assume you used 50 ml of water for washing? The solubility of aspirin in water is 0.33 g per 100 ml at room temp.

0.33/100 x50 = 0.165 g

Calculate the partition coefficient if the concentration of the ethanol in the organic layer is 0.02M and the concentration of ethanol in the aqueous layer is 0.04M. K =

0.5

Calculate the partition coefficient if 1/2 of a 10% ethanol sample is extracted from the aqueous phase with 1-pentanol.

1 because 50% in aqueous and 50% in organic

1 only Answer Key: F Feedback:Remember, there must be both the conjugate acid and base present after mixing has occurred.

what is an appropriate injection size for GC?

1-10 uL

100 % Pentanol

In today's experiment you will rinse your syringe with which of the following after each injection? (exp 1)

Calculate the mass of the reaction mixture. Assume the density of the mixture is 1.03 mL^-1.

1.03 x 100.5 ml = 103.5

The titration of 25.00 mL of a vinegar sample with 0.500 N sodium hydroxide solution required 44.60 mL . Assume the density of the vinegar sample is 1.00g mL c) What is the percent acetic acid in the vinegar sample?

1.338 g -------- x 100 =5.352 % 25 g

Quality of calibration curve: How many points to use?

10-50 points

A student performing this experiment titrates 1.390 g of KHP with a NaOH solution. The initial buret reading is 0.73 mL and the final buret reading is 22.38 mL. What is the monetary of the NaOH solution? ...

1390 / (22.38-.73 ) x 204.22 = 0.3144 M

First Derivative Plot

In today's lab experiment you will construct what type of plot to determine the pKa of bromothymol blue?

You add 100 mL of 0.10 M HCl to 100 mL of 0.70 M phosphate (H2PO4-; pKa = 2.148). What is the pH of this solution? pH =

2.92|2.9|2.926|2.93 Remember to use the Henderson-Hasselbalch equation. Also, the strong acid will convert the weak base to the weak acid and this must be accounted for.

You add 100 mL of 0.20 M HCl to 100 mL of 0.50 M formate (HCOO-). What is the pH of this solution? (For HCOOH the pKa is 3.744). pH =

3.9|3.92 Remember to use the Henderson-Hasselbalch equation. Also, the strong acid will convert the weak base to the weak acid and this must be accounted for.

Calculate Delta T for the reaction. Assume the initial temperature of both reactants is 25.0 degree C

30.3-25 = 5.3 C

You add 1.00 x 102 mL of 0.10 M HCl to 1.00 x 102 mL of 0.50 M formate (HCOO-). What is the pH of this solution? For HCOOH the pKa is 3.744

4.35

Calculate the volume of the reaction mixture

50 ml + 50.5 ml = 100.5 Ml

Bromothymol blue

A pH indicator: changes color based on pH changes in solution yellow to blue

Suppose that, in an attempt to minimize waste, a laboratory teaching assistant decided to give each student only 1 mL of each liquidf for use to measure density in this experiment.

A) (1) Estimate the magnitude of the absolute error and percent error in the measured sample volumes. Compare those errors to the errors that occur when measuring volumes of approximately 8 mL, as is normally done in this experiment Assume that the graduated cylinder used to measure all of the volumes has 0.1-mL graduations. You're save assuming (0.1 / 2) mL error with 0.1 mL graduations, so +/-0.05 mL absolute error, 0.05 mL / 1 mL = 5% relative error in a 1 mL sample. With an 8 mL sample, absolute error is the same but relative error is 1/8 as large (because the sample is 8 times bigger). B) Based on your answer to (1), would you be more or less confident about your density measurement if you used the smaller sample volume, rather than the normal 8-mL sample? Breifly explain more confident knowing it would yield a closer measurment.

Studying an unknown liquid using the procedure of this experiment, a student recorded in table 2 the following data. Table 2 Volume of liquid, ml 8.30 mass of cylinder & liquid, g 45.00 mass of graduated cylinder, g 38.44 Solubility: in water i in cyclohexane s boiling point, �C 80

A) calculate the density: 45 - 38.44 = 6.56 g 6.56/8.30 = 0.79g/ml B) List the liquids in table 2 whose densities and boiling points most closely match those of the unknown liquid. List these liquids densities, boiling points, & solubilities. Propanone methanol ethanol C) Based on your evaluation of all of the data in your answer to (2), including solubilities, identify the unknown liquid. Briefly explain your reasoning. ethanol has a density of 0.789 & 78.5 boiling point and its miscible with H2O and cyclohexane

What are the goals and objectives for Experiment 2: Affinity Chromatography? (Select all that apply.) ADetermine the molecular weight of the protein using SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). B.Purify E. coli lysate using affinity chromatography. C.Quantify the amount of protein in our purified lysate using a Bradford assay. D.Determine the structure or our protein using gel electrophoresis. E. Quantify the absorption and emission maxima using UV-visible and fluorescence spectroscopies.

A, B, C

What factors influence the signal obtained from the spectrophotopmeter that you will use as the detector in Experiment 5: LC? (select all that apply) A. Path lenth of the cell B. Molar absorptivity of the pigments C. Mobile phase flow rate D. Concentration of spinach extract

A, B, C, D

What are the goals and objectives for Experiment 2: Affinity Chromatography? (Select all that apply.) A. Determine the molecular weight of the protein using SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). B. Purify E. coli lysate using affinity chromatography. C. Quantify the amount of protein in our purified lysate using a Bradford assay. D. Determine the structure or our protein using gel electrophoresis. E. Quantify the absorption and emission maxima using UV-visible and fluorescence spectroscopies.

You wish to prepare a buffer with a pH of 7.10. Which of the below combinations would be best to prepare this buffer? A. H2CO3 and HCO3- (pKa = 6.38) B. CH3CO2H and CH3CO2- (pKa = 4.74) C. HCOOH and HCOO- (pKa = 3.74) D. H3PO4 and H2PO4- (pKa = 2.12)

A. H2CO3 and HCO3- (pKa = 6.38)

You have a solution that you wish to dilute 50 times (50x). Which of the below represents a 50x dilution? A. 1.0 mL of a solution diluted to 50.0 mL B. 25 mL of a solution diluted to 100 mL C. 50 mL of the solution diluted to 1.0 mL D. 25 mL of a solution diluted to 50 mL

A. 1.0 mL of a solution diluted to 50.0 mL

If a standard addition plot was constructed for a given analysis and the linear regression gave you a slope of 0.21 and a y-intercept of 0.14. If the area under the curve was found to be 0.27 V•s, what is the percentage of ethanol in the sample? A. 1.28% B. 0.78% C. 1.5% D. 0.67%

A. 1.28%

A. 43.80 mL

In the To Dispense method, it was really important that no drops of water was lost during the transfer of liquid from the graduated cylinder to the beakers. Why? How might this influence the final result? A. Any water that is lost in the transfer is water the will not be massed. This will result in a correction factor that is too negative. B. Any water that is lost in the transfer is water the will not be massed. This will result in a correction factor that is too positive. C. Water lost will have no influence on the results or the experiment whatsoever. D. Any water that is lost in the transfer is water the will not be massed. However, this will not affect the final correction factor determined.

A. Any water that is lost in the transfer is water the will not be massed. This will result in a correction factor that is too negative.

For the To Contain method, it was important that the graduated cylinder be dry before adding any liquid to the graduated cylinder, AND it was important that no water splashed onto the walls of the graduated cylinder. Why? How might this influence your results? A. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be. B. Extra liquid in the graduated cylinder would have no effect on the results of the experiment and the correction factors will not be influenced. C. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. However, this would not influence the final correction factors that are determined. D. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more negative than it should be.

For the To Contain method, it was important that the graduated cylinder be dry before adding any liquid to the graduated cylinder, AND it was important that no water splashed onto the walls of the graduated cylinder. Why? How might this influence your results? A. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be. B. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. However, this would not influence the final correction factors that are determined. C. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more negative than it should be.Feedback: If the mass we determine is too large, we would also calculate a volume from the density formula that is too large. This would result in us calculating a correction factor that is more positive than the true correction factor should be and the values will be over-corrected. D. Extra liquid in the graduated cylinder would have no effect on the results of the experiment and the correction factors will not be influenced.

A. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be. Feedback: If the mass we determine is too large, we would also calculate a volume from the density formula that is too large. This would result in us calculating a correction factor that is more positive than the true correction factor should be and the values will be over-corrected.

___________________ is defined any analytical method that relies on measuring the mass of a substance to complete the analysis. A. Gravimetric analysis B. Background correction C. Calibration D. Volumetric analysis

A. Gravimetric analysis

Which of the following enzyme(s) will you use in today's lab? (select all that apply) A. Horseradish peroxidase B. Glucose oxidase. C. Catalase D. galactosidase E. Lactase

A. Horseradish peroxidase B. Glucose oxidase.

For LC, which of the below pieces of glassware will you use to perform the solvent-solvent extraction. A. Separatory Funnel B. The extraction will be performed in a vial. C. Erlenmeyer Flask D. Stemless Funnel E. Buchner Funnel

A. Separatory Funnel

sodium chloride (NaCl)

In today's lab, which salt will you add to your solutions in order to maximize the amount of ethanol extracted?

Which of the following statement(s) describe(s) buffer solutions? (select all that apply) A. The weak acid portion can consume strong acid to help resist pH changes B. They are capabale of resisting changes in pH C. The pKa value(s) of the reagents selected and desired buffer pH, must be within +/- 1 pH unit of each other in order to prepare a proper buffer solution. D. The weak base portion can consume strong acid to help resist pH changes E. The weak acid component can consume strong base to help resist pH changes

B, C, D, E

What factors affect the separation of compounds in gas chromatography? (select all that apply) A. Temperature of the injection port B. boiling point of compounds C. Temperature of the column D. None of these will affect separation E. flow rate of the carrier gas

B, C, E Separations are affected by column temperature, flow rate of the carrier gas, and the boiling point of the compounds.

In order to make an acetic acid/sodium acetate buffer of pH 5.76, you would use sodium acetate with which of the following (select all that apply): A. H2SO4 B. acetic acid C. NaOH D. NaCl E. HCl

B, E Remember, you can prepare the buffer by the theoretical means (conjugate acid/base pair) or by the theoretical means (weak base, add strong acid to generate conjugate acid).

Which of the following is not acid/conjugate base pairs: A. NaHSO4/Na2SO4 B. H3PO4/Na2HPO4 C. CH3COOH/NaCH3COO D. NaHCO3/Na2CO3

B. H3PO4/Na2HPO4

Calculate the partition coefficient if 1/2 of a 10% ethanol sample is extracted from the aqueous phase with 1-pentanol. (Hint: K = [CH3CH2OH]org / [CH3CH2OH]aq) A. 0.33 B. 1.0 C. 0.66 D. 0.5

B. 1.0

You have a solution that you wish to dilute 50 times (50x). Which of the below represents a 50x dilution? A. 50 mL of the solution diluted to 1.0 mL B. 1.0 mL of a solution diluted to 50.0 mL C. 25 mL of a solution diluted to 100 mL D. 25 mL of a solution diluted to 50 mL

B. 1.0 mL of a solution diluted to 50.0 mL

How will you determine when to switch mobile phases during your chromatographic run for Experiment 5: LC? A. Go by the time scale on the chromatogram provided in your lab manual. B. After the appearance of the correct number of peaks as indicated in the chromatogram in your lab manual. C. The spectrophotometer will prompt you as to when to switch the mobile phases. D. When the voltage on the chromatogram in your lab manual is the same as the voltage of your recorded data.

B. After the appearance of the correct number of peaks as indicated in the chromatogram in your lab manual.

What precautions should be taken when using separatory funnel for your extraction? A. Aim the end of the funnel toward your face so you can see it well. B. Aim the end of the funnel toward the back of your hood. C. Leave the stopcock on when draining the funnel to keep air out. D. Vent to release pressure immediately after adding solvents together.

B. Aim the end of the funnel toward the back of your hood. D. Vent to release pressure immediately after adding solvents together.

In affinity chromatography, the purpose of the imidazole in the elution buffer is to: A. Increase the polarity of the mobile phase to cause bands to elute more quickly. B. Displace the protein from the Ni2+ sites on the Ni-NTA resin. C. Remove any weakly-bound impurities from the Ni2+ sites on the Ni-NTA resin. D. Clean the column and to prepare it for storage.

B. Displace the protein from the Ni2+ sites on the Ni-NTA resin.

For both types of calibration curves you will make this week, which of the following plots to achieve the goal of the experiment? A. Retention Time vs Ethanol Peak Area B. Ethanol Peak Area vs Percent of Ethanol C. 1-Pentanol Peak Area vs Percent of Ethanol D. Retention Time vs Percentage of Ethanol

B. Ethanol Peak Area vs Percent of Ethanol

Which is the weakest acid based on pKa? A. Ka = 3.95 x 10^-5 B. Ka = 6.05 x 10^-10 C. Ka = 1.03 x 10^-2 D. Ka = 5.73 x 10^-7

B. Ka = 6.05 x 10-10 Remember that pKa = -log(Ka), and that the higher the pKa, the weaker the acid.

Why does bromothymol blue change color when the pH shifts from acidic to basic? A. There is a change in the equilibrium constant of the acidic and basic forms. B. Upon the loss of a proton, there is a structural rearrangement within the molecule that changes the electronic structure of the molecule. C. There is an increase in the concentration of the bromothymol blue as the irreversible reaction proceeds to completion. D. The atoms move with in the molecule.

B. Upon the loss of a proton, there is a structural rearrangement within the molecule that changes the electronic structure of the molecule.

When using the autopipette and autopipette tips, you should do which of the following? A. When switching to a new reagent you want to dispense, rinse the pipette tip with some of the new reagent first to clean the pipette tip and then start to draw up new reagent and dispense. B. Use a new tip for each type of reagent you wish to draw up and dispense. C. Rinse the pipette tips before moving to a new reagent. D. Use a new tip every time you pipette, so you do not contaminate the reagents.

B. Use a new tip for each type of reagent you wish to draw up and dispense.

What types of samples are ideal for GC? A. Proteins and carbohydrates B. Volatile compounds. C. Aqueous samples D. Non-volatile compounds

B. VOLATILE COMPOUNDS

What of the following is NOT a reason for which the calibration of laboratory glassware important? A. It provides us with information about how our specific glassware measures the quantity in question as opposed to what the manufacturer claims it can do. B. It increases the accuracy of our measurements so that our measurement lies closer to the true value of the quantity of interest. C. It increases the precision of our measurements and ensures that the results are repeatable. D. The calibration of glassware and equipment ensures that the answers we arrive at after the experiment is complete is a better reflection of the true answer.

C. It increases the precision of our measurements and ensures that the results are repeatable. Feedback: Correct! While the act of repeating many calibration trials may allow us to more precisely know the quantity we are measuring, the act of calibration is not designed to lend more precision to our results. Instead, it is designed to give us more confidence that the value we measure is closer to the true value of the quantity of interest.

Mathematically buffer capacity is defined as: A. β = dCacid / dpH = dpH / dCbase B. none of these are correct C. β = - dCacid / dpH = dCbase / dpH D. β = dCacid / dpOH = - (dCbase / dpH)

C. β = - dCacid / dpH = dCbase / dpH

In affinity chromatography, the purpose of the imidazole in the elution buffer is to: A. Remove any weakly-bound impurities from the Ni2+ sites on the Ni-NTA resin. B. Increase the polarity of the mobile phase to cause bands to elute more quickly. C. Displace the protein from the Ni2+ sites on the Ni-NTA resin. D. Clean the column and to prepare it for storage.

C. Displace the protein from the Ni2+ sites on the Ni-NTA resin.

In experiment 5: LC, the system is stored using mobile phase 3. Before making any injection onto the column, the mobile phases are switched to mobile phase 1, and 20 minutes must pass before the column can be used. Why? A. The purpose of waiting is to flush the column of any residual pigments from previous chromatographic separations. B. To ensure that no air entered into the system while switching mobile phases. C. This is to allow the column to be flushed of mobile phase 3 and to allow the stationary phase to equilibrate with mobile phase 1. D. There is no reason to wait.

C. This is to allow the column to be flushed of mobile phase 3 and to allow the stationary phase to equilibrate with mobile phase 1.

C. 2.5 M

Beers law is mathematically defined as: A. A = (bC)/ελ B. log (T) = ελbC C. A = ελbC D. A = ελ / (bC)

C. A = ελbC

What indicator molecule are we using in today's experiment? A. Bromocresol blue B. Dextran blue C. Bromothymol blue D. Hemoglobin

C. Bromothymol blue

The rate of a molecule's movement in an electric field is a function of all of the following EXCEPT: A. Average net charge B. Molecular size C. Concentration D. Molecular shape

C. Concentration

In the presence of horseradish peroxidase and H2O2, _____________ is oxidized. A. Ferricyanide B. Both ferricyanide and and ferrocyanide C. Ferrocyanide D. D-Glucolactone

C. Ferrocyanide

In today's lab experiment you will construct what type of plot to determine the pKa of bromothymol blue? A. Standard calibration plot. B. Standard addition plot C. First Derivative Plot D. Second Derivative Plot E. Titration Curve

C. First Derivative Plot

Glucose oxidase catalyzes the reaction of ___________ with O2? A. Fructose. B. Sucrose C. Glucose D. All of the above E. A and B F. A and C

C. GLUCOSE

___________________ is defined any analytical method that relies on measuring the mass of a substance to complete the analysis. A. Volumetric analysis B. Background correction C. Gravimetric analysis D. Calibration

C. Gravimetric analysis

how much light a molecule absorbs at a particular wavelength.

Molar absorptivity provides information about:

A student was given only one graduated cylinder to use for this experiment. After using it to measure 50.0 mL of the assigned acid, the student failed to rinse or dry the cylinder before measuring out the 50.5 mL of the base. would the calculated change in Heat Neutralization be higher, lower, or the same as the literature for change in heat neutralization. Briefly explain this difference as a result of using only one graduated cylinder for the experiment.

Calculated H neutzn will be higher since cylinder used without rinsing contains little acid which will react with the base this will make base's strength lesser than the original. & Now when you will do titration (neuralization) the base required will be more than the actual. where actually the base used should be less and actual concentration of H therefore should have been less.

Gradient elution

Change the mobile phase composition over time This makes the elution process faster

Acid-base indicator

Chemical dyes whose colors are affected by acidic and basic solutions

How can you most accurately determine the actual flow rate of the mobile phase through the column?

Collect mobile phase from the column in a graduated cylinder for a specified period of time.

General idea about calibration

Comparing what is unknown to what is the known measurement of the equipment or substance

bromothymol blue structure

Conjugation changes between protonated vs. deprotonated structures protonated form doesn't have conjugation due to ring deprotonated form does not does not have that ring that contains the sulfur atom

You add 1.00 x 102 mL of 0.10 M HCl to 1.00 x 102 mL of 0.50 M formate (HCOO-). What is the pH of this solution? For HCOOH the pKa is 3.744 A. 3.14 B. 0.69 C. 3.744 D. 4.35 E. 5.62

D Remember to use the Henderson-Hasselbalch equation. Also, the strong acid will convert the weak base to the weak acid and this must be accounted for.

D. 8.20 x 103 M-1 cm-1

You wish to prepare a buffer with a pH of 5.25. Which of the below combinations would be best to prepare this buffer? A. HCOOH and HCOO- (pKa = 3.74) B. H3PO4 and H2PO4- (pKa = 2.12) C. H2CO3 and HCO3- (pKa = 6.38) D. CH3CO2H and CH3CO2- (pKa = 4.74)

D. CH3CO2H and CH3CO2- (pKa = 4.74)

What of the following is NOT a reason for which the calibration of laboratory glassware important? A. The calibration of glassware and equipment ensures that the answers we arrive at after the experiment is complete is a better reflection of the true answer. B. It provides us with information about how our specific glassware measures the quantity in question as opposed to what the manufacturer claims it can do. C. It increases the accuracy of our measurements so that our measurement lies closer to the true value of the quantity of interest. D. It increases the precision of our measurements and ensures that the results are repeatable.

D. It increases the precision of our measurements and ensures that the results are repeatable.

In affinity chromatography, the purpose of the imidazole in the elution buffer is to: A. Clean the column and to prepare it for storage. B. Increase the polarity of the mobile phase to cause bands to elute more quickly. C. Remove any weakly-bound impurities from the Ni2+ sites on the Ni-NTA resin. D. Displace the protein from the Ni2+ sites on the Ni-NTA resin.

D. Displace the protein from the Ni2+ sites on the Ni-NTA resin.

You take 15.0 mL of your unknown solution and dilute it to 250. mL. You then determine that the concentration of this diluted sample is 0.30 M. What was the concentration of the original (undiluted) sample? A. 0.050 M B. 0.018 M C. 55.6 M D. 5.0 M

D. 5.0 M

xanthophylls → chlorophylls → carotenes

In what order should the plant pigments elute from the C-18 column in Experiment 5: LC?

For the To Contain method, it was important that the graduated cylinder be dry before adding any liquid to the graduated cylinder, AND it was important that no water splashed onto the walls of the graduated cylinder. Why? How might this influence your results? A. Extra liquid in the graduated cylinder would have no effect on the results of the experiment and the correction factors will not be influenced. B. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more negative than it should be. Feedback: If the mass we determine is too large, we would also calculate a volume from the density formula that is too large. This would result in us calculating a correction factor that is more positive than the true correction factor should be and the values will be over-corrected. C. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. However, this would not influence the final correction factors that are determined. D. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be.

D. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be.

You wish to prepare a buffer with a pH of 4.00. Which of the below combinations would be best to prepare this buffer? A. H2CO3 and HCO3- (pKa = 6.38) B. CH3CO2H and CH3CO2- (pKa = 4.74) C. H3PO4 and H2PO4- (pKa = 2.12) D. HCOOH and HCOO- (pKa = 3.74)

D. HCOOH and HCOO- (pKa = 3.74)

Which of the following combinations would be best to buffer the pH to 9.00? A. H3PO4 and H2PO4- (pKa = 2.12) B. CH3CO2H and CH3CO2- (pKa = 3.75) C. HNO2 and NO2- (pKa = 3.35) D. NH4+ and NH3 (pKa = 9.24) E. H2PO4- and HPO42- (pKa = 7.20)

D. NH4+ and NH3 (pKa = 9.24)

Which one of these is not a buffer? A. A solution of weak acid to which its conjugate base is added B. A solution of weak acid to which strong base is added such that the concentration of strong base is less than the concentration of weak acid C. A solution of weak base to which strong acid is added such that the concentration of strong acid is less than the concentration of weak base D. The partial dissociation of a weak acid in solution

D. The partial dissociation of a weak acid in solution

Molar absorptivity provides information about: A. how much a molecule absorbs at all visible wavelengths. B. the concentration of a molecule within a sample C. the amount of sample that interacts with light at a particular wavelength. D. how much light a molecule absorbs at a particular wavelength.

D. how much light a molecule absorbs at a particular wavelength.

In what order should the plant pigments elute from the C-18 column in Experiment 5: LC? A. chlorophylls → carotenes → xanthophylls B. carotenes → chlorophylls → xanthophylls C. xanthophylls → carotenes → chlorophylls D. xanthophylls → chlorophylls → carotenes

D. xanthophylls → chlorophylls → carotenes

When in its acidic form, a solution of bromothymol blue appears: A. green B. orange C. blue D. yellow

D. yellow

Would diluting the solution affect its buffer capacity?

Diluting a buffer solution would decrease its buffer capacity. There is a smaller concentration of acid and base because you have fewer moles of weak acid and weak base available

In affinity chromatography, the purpose of the imidazole in the elution buffer is to

Displace the protein from the Ni2+ sites on the Ni-NTA resin.

calibrating process for TD

Does not need to be dry because it accounts for the droplets that will left behind after pouring Get a clean dry beaker Place dry beaker on scale Add 10mL of water to the TD graduated Transfer all of the liquid from the TD to the beaker Remeasure beaker with water in it

What are the forces that dictate the how the pigments will separate along the column?

Electrostatic and Dipole-Dipole

elution order in GC and why

Ethanol, water and pentanol because of boiling point (ethanol has the lowest and pentanol has the highest)

During a liquid-liquid extraction, the solvent with the lowest density will be on the bottom.

False

how is absorbance related to ferricyanide concentration

If ferrocyanide increases then the absorbance will increase and if it decreases then the absorbance will decrease

Mobile phase 3, mobile phase 2, mobile phase 1

In Experiment 5 LC, the mobile phases that you will use in order of least polar to most polar are:

dye, bind to

In a Bradford assay, you will measure the UV/visible absorption changes of a dye (dye or protein) as they bind to (bind to or separate from) each other.

polar, non-polar

In a normal phase LC experiment, the stationary phase is polar (polar/non-polar) and the mobile phase is non-polar (polar/non-polar).

Displace the protein from the Ni2+ sites on the Ni-NTA resin.

In affinity chromatography, the purpose of the imidazole in the elution buffer is to:

HCl & acetic acid

In order to make an acetic acid/sodium acetate buffer of pH 5.76, you would use sodium acetate with which of the following (select all that apply):

Any water that is lost in the transfer is water the will not be massed. This will result in a correction factor that is too negative.

Ferrocyanide Ferrocyanide is oxidized by horseradish peroxidase (Remember Ferro vs Ferricyanide (Ferro is the compound oxidized)). Please see the first few pages of Expt. 6 in the lab manual for more details.

In the presence of horseradish peroxidase and H2O2, _____________ is oxidized.

A student doing this experiment was puzzled by the fact that while each of the individual solutions being used is dangerous the mixture could be safely disposed of by pouring it into the drain and diluting with a large amount of running water. Describe the hazards of each of the solutions. Explain why the mixture is not as hazadhous as the original solution from a waste disposal point of view.

It could be that each of the individual solutions neutralize on addition of water. The heat of reaction would be very high hence making the solution dangerous. After mixing and diluting with a large amount of running water, most of the heat would be dissipated.

Why do you think the pH of the theoretical buffer was off from the prediction? What factors contributed to this difference?

It was off because this is the pH if everything was perfect however there are outside factors Solids are known to be hygroscopic meaning they absorb water If it was humid in the lab then the solids would absorb water so you would weigh out less actual solid and more water and therefore you would have fewer moles in solution than calculated by the HH Carbon dioxide from the air can dissolve in the solution and can change the pH Can be caused by vigorous stirring in the beaker which dissolves carbon dioxide and causes pH to decrease Errors with the scale, what was measured is not what was exactly used changes in Temperature

Calculate the partition coefficient if the concentration of the ethanol in the organic layer is 0.02M and the concentration of ethanol in the aqueous layer is 0.04M.

K=0.5

Gas Chromatography is a great technique for the analysis of what types of samples?

Liquid samples that are volatile and low boiling point

pros and cons of a having a low or high number of points for the calibration curve

Low wouldn't be as effective for making a trendline but would take a shorter amount of time High more accurate trendline

β = - dCacid / dpH = dCbase / dpH

Mathematically buffer capacity is defined as:

Why did the purified GFP not bind to the resin and why was the solution not colored like the others

Maybe the interaction between the protein's polyHis tag and the resin was weak and we broke that bond during the native wash buffer so we didn't collect much when we did the elution buffer

reverse phase chromatography

Means stat phase is nonpolar and mobile phase is polar Polar molecules will elute from the column first Nonpolar pigments will interact more favorably with the column and polar pigments will interact more favorably with the mobile phase

In Experiment 5 LC, the mobile phases that you will use in order of least polar to most polar are:

Mobile phase 3, mobile phase 2, mobile phase 1

Why is the buret rinsed with the sodium hydroxide solution prior to filling with solution?

NaOH ensures that all water or acid previously used in the buret is removed so you can have the correct balance.

calibrating process for TC

Needs to be clean and dry Record dry weight of the cylinder Determine the temperature of water Add water to the graduated cylinder in 10 mL increments Weighing the cylinder and water for every additional Important to minimize water that gets on the sides because they will influence the results

the densty of air at 100 C is less than 1 gram is it reasonable to assume the vaporized liquid will forse all of the air out during heating?

No, it won't. The amount of air forced out will be equal to the amount of water vapor produced The amount does not increase with temperature past 100 degrees Celsius, so SOME of the air will be forced out, but not all.

During a liquid-liquid extraction, the solvent with the lowest density will be on the top. TrueFalse

True

how you quantitatively transfer solid to beaker

Rinse weigh paper with water to get any residue

A. the volatility of a the components of the mixture C. the molecular interactions of the compounds with the stationary phase due to differing polarities

Separation in gas chromatography is based on:

A desiccant, or drying agent, is often added to aspirin in order to prolong the aspirin's shelf life by delaying hydrolysis. How can you easily determind if any aspirin has begun to hydrolize

Smell it, it will smell like vinegar. This is because when aspirin decomposes, acetic acid is formed, which is vinegar.

Does it matter if you get drops of water on the side of the TD

TD is calibrated to account for the average amount of water left behind So if there was a drop before measuring and dispensing, there would be a similar drop left afterwards too

The temperature of the injection port needs to be higher than the temperature of the column to ensure full vaporization TrueFalse

TRUE

Is it necessary for the Erlenmeyer flask to be dry before pipeting the 25.00 mL sample of vinegar in it? Explain

The Flask doesnt have to be dry when the additional sample of vinegar sol are placed in the flask because the water present will not affect the quantity of acetic acid present

(b) Why would you not allow water to contact the foil cap while you are cooling the flask and vapor with running water

The Foil might retain some water and give a false or inaccurate result

Compound X is known to absorb at 510 nm. If you dilute a solution containing Compound X by 1/3, how does the absorbance change? The same cuvet is used for all measurements.

The absorbance decreases by 1/3 its original value.

Discuss the components of the sugar solution and how the digestion process affects those components. (glucose experiment)

The acid digestion of the bonds between glucose and fructose is necessary for the glucose oxidase to catalyze the oxidation of glucose to produce hydrogen peroxide. Then, hydrogen peroxide can react with ferrocyanide catalyzed by horseradish peroxidase to produce ferricyanide. Without breaking down the sucrose, the disaccharide is not metabolized as quickly because it is not the direct substrate of glucose oxidase. Therefore, sucrose needs to be broken down into its components in order to increase the amount of free glucose available to react with the enzymes.

Why must the vinegar sample be obtained in a dry beaker?

The beaker must be dry because any water present will dilute the vinegar sample.

At what point is the buffer capacity the highest? Why? Relate it to an equation

The buffer capacity is at the highest when the pH of the buffer solution equals the pKa of the weak acid used to make the buffer solution. This is directly related to the Henderson Hasselbalch equation pH = pKa + log ( [base] / [acid] ). The pH equals the pKa when the concentration of weak acid and the concentration of its conjugate weak base are the same. he point where the buffer can equally resist changes in pH with the addition of either a strong acid or base because the concentrations of the conjugate acid-base pair are equal

How is color change of bromothymol blue related to structure

The color change occurs due to the rearrangement of bonds that occurs when the molecule loses a proton. The basic form of bromothymol blue is deprotonated, so the negative charge of the deprotonated oxygen atom is redistributed, resulting in the change in the structure of the ring containing that oxygen atom.2 This can result in various resonance forms of the basic form of bromothymol blue. Also, this rearrangement causes a broken bond in the 5 member ring that contains sulfur, which directly causes the change in color from yellow to blue.

partition coefficient, What does it tell you about the partitioning of ethanol between pentanol and water

The higher the partition coefficient (greater than 1), the higher the attraction of ethanol to the organic pentanol layer and the better the extraction of the ethanol from the sample matrix.

Explain why you would expect thatΔH neutzn for HBr reacting with NaOH solution andΔhneutzn for HNO3 reacting with KOH solution would be identical. Write appropriate equations to support this explanation.

The net ionic equations for both the reactions aresame so they have identical ΔH neutralization

Give a brief overview of how a pH meter works.

The pH meter is composed of a barrel and a glass membrane. The Glass membrane must be completely submerged in the solution in order for a measurement to be read. The barrel contains a working electrode and a silver/silver chloride reference electrode. These electrodes are ion selective and measure the electric potential of the solution through the concentration of positively charged hydronium ions in solution. The electrical potential measured is compared to the electric potentials of the solutions with known pHs that were used to calibrate the probe. The difference between these electric potentials allows the meter to determine the pH of the solution of interest.

What buffer solution do you expect to have a more accurate initial pH (practical or theoretical) and why?

The practical method was expected to produce the most accurate initial pH because the strong acid or base would be added dropwise until the pH probe indicated the solution had reached the desired pH.

Concentration

The rate of a molecule's movement in an electric field is a function of all of the following EXCEPT:

(a) How will you determine when the unknown liquid in the flask has completely vaporized?

The ring of liquid surrounding the boiling stone disappears as vaporization is complete

Standard Addition Plot

The type of plot you will construct in Day 2 of this experiment is called a ____________.

1.) Briefly explain why it is important to carry out this experiment in a well-ventilated area.

The unknown may be flammable, toxic and irritant

Briefly explain why it is important to stir the water in the hot water bath while you are determining the boiling point of a liquid.

The water is gonna heat up from the bottom up when you stir it, it lets the water heat up uniform.

Which of the following statement(s) describe(s) buffer solutions?

The weak base portion can consume strong acid to help resist pH changes The weak acid component can consume strong base to help resist pH changes C.The pKa value(s) of the reagents selected and desired buffer pH, must be within +/- 1 pH unit of each other in order to prepare a proper buffer solution. They are capabale of resisting changes in pH

By which method would you calibrate a 100-mL volumetric flask?

To Contain

dAbsorbance/dpH vs. Average pH

To determine the pKa of the bromothymol blue, you will construct a plot of _____________.

Would the measured boiling point of your unknown liquid have been too high or too low if the thermometer bulb had rested on the bottom of the water-filled beaker? briefly explain.

Too high because it would be measuring the tempurature of the glass, not the water.

For the To Contain method, it was important that the graduated cylinder be dry before adding any liquid to the graduated cylinder, AND it was important that no water splashed onto the walls of the graduated cylinder. Why? How might this influence your results? A. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more positive than it should be. B. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. However, this would not influence the final correction factors that are determined. C. Extra liquid in the graduated cylinder would have no effect on the results of the experiment and the correction factors will not be influenced. D. Extra liquid in the graduated cylinder would mean that mass of water we obtained for a given reading would be higher than expected. This would potentially result in a correction factor that is more negative than it should be.

In affinity chromatography, the purpose of the imidazole in the elution buffer is to: A. Displace the protein from the Ni2+ sites on the Ni-NTA resin. B. Remove any weakly-bound impurities from the Ni2+ sites on the Ni-NTA resin. C. Increase the polarity of the mobile phase to cause bands to elute more quickly. D. Clean the column and to prepare it for storage.

The spectrophotometric enzyme assay ___________________? A. Indirectly determines the amount of glucose in the solution. B. Directly determines the amount of glucose in the solution. C. Involves one enzymatic reaction. D. Is not useful in this experiment.

Which of the following is not acid/conjugate base pairs: A. H3PO4/Na2HPO4 B. NaHSO4/Na2SO4 C. NaHCO3/Na2CO3 D. CH3COOH/NaCH3COO

In a Bradford assay, you will measure the UV/visible absorption changes of a _____ as they ____ each other

a dye, bind to

In today's lab, you are indirectly determining the concentration of the following (select all that apply) A. Glucose B. Sucrose C. Fructose D. Lactose

a glucose

molar absorptivity

a measure of how strongly the sample absorbs light at a particular wavelength.

Buffer capacity

a measure of how well a buffered solution resists pH change with the addition of a strong acid or strong base when pH lower than pka, buffer is better at resisting basic changes At buffer pH less than pka you expect it is a more accurate buffer when it is closer to the pka

solvent solvent extraction

a separation technique that exploits differences in analyte polarity or charge to separate the analytes into different liquids solvents must be immiscible

***A student following the procedure of this experiment obtained the following data for an unknown volatile liquid: mass of flask, boiling stone, foil cap and unknown after cooling 83.350 mass of flask, boiling stone, and foil cap, g 82.657 water bath temperature, °C 95.0 barometric pressure, in Hg 30.09 volume of flask, mL 270 accepted molar mass of unknown, g mol 86.2

a) mass of unknown 83.350-82.657= 0.693 g b)Temperature in K 95 + 273.15= 273.15 ? c)barometric pressure in atm 30.09/760= 0.0396 d)vol of the flask in liters 270/1000= 0.27 L e)density 0.693/0.27 = 2.57 f) MM of vaporized : g)percent error:

abc

What factors influence the signal obtained from the spectrophotopmeter that you will use as the detector in Experiment 5: LC? (select all that apply) A. Mobile phase flow rate B. Molar absorptivity of the pigments C. Path lenth of the cell D. Concentration of spinach extract

abcd

Which is the weakest acid based on pKa? A. Ka = 3.95 x 10-5 B. Ka = 1.03 x 10-2 C. Ka = 6.05 x 10-10 D. Ka = 5.73 x 10-7

Gravimetric analysis

an analytical technique based on the measurement of mass used to determine volume of water contained or dispensed by the TC and TD

State what aqueous NaOH and KOH have incommom.

aqueous NaOH and KOH haveOH- ion in common.

The rate of a molecule's movement in an electric field is a function of what?

average net charge molecular size and molecular shape

Beers law is mathematically defined as: A. log (T) = ελbC B. A = ελbC C. A = ελ / (bC) D. A = (bC)/ελ

If a piece of glassware breaks during your experiment, the first thing you should do is: A. Pick up the broken pieces of glass and dispose of the in the glass waste box. B. Inform the TA and ask for assistance. C. Go to Morehead 102 and purchase your replacement glassware. D. Sweep up the broken pieces and dispose of them in the glass waste box.

Mathematically buffer capacity is defined as: A. β = dCacid / dpOH = - (dCbase / dpH) B. β = - dCacid / dpH = dCbase / dpH C. β = dCacid / dpH = dpH / dCbase D. none of these are correct

The rate of a molecule's movement in an electric field is a function of all of the following EXCEPT: A. Molecular shape B. Concentration C. Molecular size D. Average net charge

When using the autopipette and autopipette tips, you should do which of the following? A. Use a new tip every time you pipette, so you do not contaminate the reagents. B. Use a new tip for each type of reagent you wish to draw up and dispense. C. Rinse the pipette tips before moving to a new reagent. D. When switching to a new reagent you want to dispense, rinse the pipette tip with some of the new reagent first to clean the pipette tip and then start to draw up new reagent and dispense.

Which of the below is the correct Henderson-Hasselbalch equation? A. pH = pKa + Log [HA]/[A-] B. pH = pKa + Log [A-]/[HA] C. pKa = pH - Log [HA]/[A-] D. pKa = pH + Log [A-]/[HA]

Solvent-Solvent extraction is used to do the following: (Select all that apply) A. Analyze every compound within a mixture. B. Separate the compound of interest (analyte) from the rest of the sample (the sample matrix). C. Avoid interference with other compounds in the sample. D. Analyze a particular component within a complex mixture.

bcd

Briefly explain why it was not necessary for you to determine the mass of unknown liquid that you transferred to the flask before heating.

because, as you heat this gas, you are creating sufficient vapor to drive out the air so to have the vapor of the liquid present,the test tube will contain only the vapor that you require to calculate the molar mass.

what causes the color change of the coomassie brilliant blye g-250 dye?

binding of the dye to the protein of interest

how do enzymes catalyze reactions?

by lowering the activation energy required for the reaction to occur

In Day 1 of this lab you will prepare your standard solutions in which of the following? A. Capped vials with tops that can be pierced with a GC syringe. B. Erlenmeyer flasks, with Parafilm sealing the tops. C. Volumetric flasks. D. Beakers with Parafilm sealing the top.

practical method

choosing either the weak acid or weak base from the selected regents based on their pKa and the desired pH adding dropwise addition of either the strong acid or strong base to partially neutralize the weak species. Keep adding until pH probe indicates desired pH was reached

statement of error and improvement should be included in the

conclusion

What hazards should you know about when you work with: 6M HCl used in part V of this experiment? ... ...

corrosive toxic and could burn

What hazards should you know about when you work with: (a) Your NaoH solution? ...

corrosive toxic and could burn

If a standard addition plot was constructed for a given analysis and the linear regression gave you a slope of 1.5 and a y-intercept of 4, what is the percentage of ethanol in the sample? A. 4.5% B. 0.5% C. 1.5% D. 2.67%

What is the primary goal of the first part of this experiment (Day 1)? A. To determine an unknown amount of ethanol in your sample. B. To simply observe the separation of components in your sample. C. To determine the amount of ethanol extracted from the extraction sample. D. To determine the partition coefficient of ethanol between water and pentanol.

Which of the following are true at the inflection point of the absorbance vs. pH plot? A.[HIn] = [In-] B. The isoelectric point (pH) has been reached. C. pH = pKa D. Both A and C

Which of the following combinations would be best to buffer the pH to 9.00? A. HNO2 and NO2- (pKa = 3.35) B. H2PO4- and HPO42- (pKa = 7.20) C. H3PO4 and H2PO4- (pKa = 2.12) D. NH4+ and NH3 (pKa = 9.24) E. CH3CO2H and CH3CO2- (pKa = 3.75)

You take 2.5 mL of your unknown solution and dilute it to 200. mL. You then determine that the concentration of this diluted sample is 0.25 M. What was the concentration of the original (undiluted) sample? A. 320 M B. 0.0031 M C. 0.050 M D. 20. M

Calculate the heat transferred from the reaction of 50.0 mL of 1.00 M HNO_3 with 50.5 mL of 1.00 M NaOH solution. Assume the heat capacity of the mixture is 3.9 j g^-1 deg^-1

dH = - 103.5 grams(3.89J/g-C)(31.5 - 24.7C) dH = - 103.5 grams(3.89J/g-C)(6.8C) dH = - 2738 J

**Calculate Delta H_neutzn in joules per mole for the reaction of 1.00 mol of HNO_3 with 1.00 mol of NaOH.

dH = - 2738 J / 0.050 mole dH = -54,756 J /mol your asnswer is: dH = -54.8 kiloJoules

if we decrease [enzyme] do we expect [ferricyanide] at 420 nm to increase or decrease?

decrease

how will decreasing enzyme concentration affect amount of ferricyanide produced?

decrease ferricyanide

how will decreasing reaction time affect amount of ferricyanide produced?

decrease ferricyanide Decreasing amount produced

how will decreasing reaction temperature affect amount of ferricyanide produced?

decrease ferricyanide This is because as you lower the temperature, enzymatic activity decreases because there would not be enough energy to overcome the activation energy of the reaction in order for it to proceed.

what are the axes (y vs x) for the first derivative plot?

delta absorbance/delta pH vs average pH

why is SDS added to a protein sample

denatures the protein to get rid of shape, coats with a negative charge so they have the same charge (distributes evenly)

goals of the glucose lab

determine the concentration of glucose in gatorade determine the effect of reaction temperature, reaction time, enzyme concentration, digest vs. undigested sugar on the concentration of glucose

why was determining the pka of bromothymol blue important?

determining the pKa of bromothymol blue was important due to its role as an acid-base indicator. The pKa is the point where the bromothymol blue should change color from yellow to blue, or vice versa, allowing researchers to visibly determine the transition from acid to base.

How will you determine whether you need to clean your buret before beginning the experiment?

if there are any water dropplets in the inner surface

how did we prepare the standard solutions for the beer lab?

in Volumetric flasks and then poured into capped vials

how will increasing glucose concentration affect amount of ferricyanide produced?

increase ferricyanide concentration

which best describes the structural change in bromothymol blue that leads to it absorbing lower energy light?

increase in the conjugation upon deprotonation

Indirect enzyme assay (glucose experiment)

indirectly measuring glucose by measuring ferricyanide

what could be responsible for peaks overlapping in the GC data?

injecting the sample slowly

Calibration

is defined as the process of relating the actual physical quantity (such as volume) to the quantity indicated on the scale of an instrument.

Purpose of solvent solvent extraction

isolate the desired analyte concentrate the desired analyte separate the analyte to avoid interference with other species

why is helium gas used as the carrier gas in the GC?

it is unreactive

methods in LC experiment

liquid-liquid extraction liquid chromatography UV-Vis

Why did the basic form of bromothymol blue favor the aqueous layer?

the change of the basic form was stabilized by the polarity of water

How will you recognize the end point of your titration of KHP solution with NaOH solution?

the pink color will be in the titration mixture

titrant

the standard solution added to the sample in a titration

In this experiment you are trying to determine: bromothymol blue

the wavelength at which the acidic and basic forms of bromothymol blue absorb maximally. the pKa of bromothymol blue

a student who was in a hurry to complete this experiment didn't completely dry the crystalline product before the final weighing. how would this error affect the calculated percent yield of the experiment?

the weigh will be higher causing a yeild over 100%

the student in (1) didn't bother to cool the water used to wash the crystals. how would this error affect the calculated percent yield of the experiment?

the yeild would go down because warm water might dissolve the cristals

what aspect of the column eluents is measured in order to generate the GC data?

thermal conductivity

what is dead time?

time it takes for unresolved compounds to elute

why do we use acid to digest the sugar solution?

to break up sucrose (sucrose is made of glucose and fructose. only glucose can be oxidized and when undigested it can't be oxidized but when digested it can be)

why do we need horseradish peroxidase?

to induce a color change

what is the purpose of the Mobile phase with 250 mM imidazole?

to out compete with the chelated polyhistidine tags and elute our proteins

what is the purpose of the porous frit in the affinity chromatography column?

to secure the stationary phase and allow the mobile phase to pass

During a liquid-liquid extraction, the solvent with the highest density will be on the bottom. True False

true

The higher the partition coefficient, the better the solvent is able to extract analyte from the sample matrix. True False

master

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