NYU Chem Lab Final

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The correct procedure for transferring liquid with a volumetric pipet. 1. First clean and rinse your pipet with tap water and do a second rinse with deionized water. 2. Compress the rubber bulb and place it carefully over the upper end of the pipet. The bulb only needs to cover the end of the pipet to create an airtight seal, there is no need to push the pipet farther into the bulb. You may want to lubricate the hole of the rubber bulb with a drop of deionized water. 3. Place the tip of the pipet in the liquid and draw the liquid into the pipet and above the calibration line. Keep the pipet tip submerged to avoid air bubble entry. Be careful not to draw the liquid into the bulb. Dispose of this first amount of liquid into a waste beaker. 4. Once again, draw in the liquid to be measured above the calibration line in the pipet. Remove the bulb while simultaneously covering the tip of the pipet with your finger. Now allow the liquid level to drop to the required level by slowly allowing air to enter the pipet by a controlled lifting of the finger that is covering the end of the pipet. 5. When the liquid level is at the correct place, move the pipet tip to the glassware where you want the liquid delivered and release your finger. Allow the pipet to drain into the container and touch off any last drop on the pipet side of the glassware. 6. There may be some liquid remaining in the pipet tip. Do no blow this remaining liquid from the pipet. The pipet was calibrated to deliver the correct volume with this liquid remaining. There is a tiny bit of liquid left inside the end of the pipet after the pipet has drained: You should blow through the pipet to drain this last drop so that your transfer will be accurate. You should touch any hanging drop of solution to the side of your beaker, but leave the small amount within the pipet. You should use a graduated cylinder instead, they're more precise than a volumetric pipet.

You should touch any hanging drop of solution to the side of your beaker, but leave the small amount within the pipet.

What makes dyes water soluble

dyes are sodium salts of sulfonic or carboxylic acids.

Characteristics of good choice of solvent for separation

yields a result with significantly different Rf values for each component, giving high resolution.

The equation for a straight line is y = mx+b, where b is the y-intercept of the line. Given that Beer's law is A = εbc, what is the y-intercept of a Beer's law plot? b, the path length A, the absorbance ε, the molar absorptivity zero

zero

The following data was collected by a student performing the DETERMINING THE MOLAR ENTHALPY OF NEUTRALIZATION portion of the experiment. 50.00 mL of a 0.333 M acid is combined with 50.00 mL of 0.335 M NaOH. Before the reaction, the acid and base are at a temperature of 21.42 ºC. After mixing, the neutralized solution reaches a maximum temperature of 23.48 ºC in a calorimeter (Ccal=63.2 J/ºC). The neutralized solution has a specific heat of 3.80 J/gºC and a density of 1.11 g/mL. What is the molar enthalpy of neutralization in kJ/mol?

-60.0 kJ/mol

A 50mL volumetric flask is calibrated to the _______ and will hold exactly _________ when filled to the calibration line:

0.01 mL, 50.00 mL

The experiment described in the procedure was performed using a sample of Zinc with HCl(aq). The lab conditions were 25.00 °C, and 755.0 torr barometric pressure. 225.0 mg of Zinc (MM: 65.39 g/mol) was reacted with 30.00 mL of 0.750M HCl(aq). 87.430 g of water was collected when the reaction was complete, and it required 31.55 mL of 0.500 M NaOH(aq) to titrate the reaction mixture. Water at 25.00 °C has a density of 0.9970 g/cm3, and a vapor pressure of 23.80 torr. The value for R is 0.082058 L•atm/mol•K. What is the volume of H2(g) generated?

0.08769 L

One possible method for the determination of glucose concentration is based on the formation of a blue-green complex of glucose with o-toluidine in glacial acetic acid. The reaction is as follows: HOCH2(CHOH)4CHO(glucose) + H2N(C6H4)CH3 (o-toluidine)↔ HOCH2(CHOH)4CH=N(C6H4)CH3(blue-green complex) + H2O A stock solution was prepared by dissolving and diluting 0.668 g of glucose (MM=180.156 g/mol) to 100.00 mL with deionized water. A dilution was prepared from the stock solution by treating 5.00 mL of the stock solution with o-toluidine and diluting to 100.00 mL with deionized water. Colorimetric determination gave that the transmittance of the sample was 81.2% when the path length of the light through the solution was exactly 1 cm. Calculate the Absorbance for the species.

0.0904

One possible method for the determination of glucose concentration is based on the formation of a blue-green complex of glucose with o-toluidine in glacial acetic acid. The reaction is as follows: HOCH2(CHOH)4CHO(glucose) + H2N(C6H4)CH3 (o-toluidine)↔ HOCH2(CHOH)4CH=N(C6H4)CH3(blue-green complex) + H2O A stock solution was prepared by dissolving and diluting 0.725 g of glucose (MM=180.156 g/mol) to 100.00 mL with deionized water. A dilution was prepared from the stock solution by treating 15.00 mL of the stock solution with o-toluidine and diluting to 100.00 mL with deionized water. Colorimetric determination gave that the transmittance of the sample was 55.2% when the path length of the light through the solution was exactly 1 cm. Calculate the Absorbance for the species.

0.258

The following data was collected by a student performing the DETERMINING THE SPECIFIC HEAT CAPACITY AND MOLAR HEAT CAPACITY OF COPPER portion of the experiment. A 31.66 g copper coil is removed from boiling water and is immediately immersed in a calorimeter with a constant of 68.4 J/ºC. The calorimeter contains 73.21 g of water that is initially at 23.83 ºC. The system reaches equilibrium at a temperature of 26.31 ºC. What is the specific heat of the copper? (Specific heat of water is 4.184 J/gºC., Molar mass of copper= 65.39 g/mol)

0.398 J/gºC

One possible method for the determination of glucose concentration is based on the formation of a blue-green complex of glucose with o-toluidine in glacial acetic acid. The reaction is as follows: HOCH2(CHOH)4CHO(glucose) + H2N(C6H4)CH3 (o-toluidine)↔ HOCH2(CHOH)4CH=N(C6H4)CH3(blue-green complex) + H2O A stock solution was prepared by dissolving and diluting 0.875 g of glucose (MM=180.156 g/mol) to 100.00 mL with deionized water. A dilution was prepared from the stock solution by treating 18.00 mL of the stock solution with o-toluidine and diluting to 100.00 mL with deionized water. Colorimetric determination gave that the transmittance of the sample was 31.7% when the path length of the light through the solution was exactly 1 cm. Calculate the Absorbance for the species.

0.499

The experiment described in the procedure was performed using a sample of Calcium with HCl(aq). The lab conditions were 25.00 °C, and 747.0 torr barometric pressure. 112.7 mg of Calcium (MM: 40.08 g/mol) was reacted with 25.00 mL of 1.25M HCl(aq). 71.560 g of water was collected when the reaction was complete, and it required 34.53 mL of 0.750 M NaOH(aq) to titrate the reaction mixture. Water at 25.00 °C has a density of 0.9970 g/cm3, and a vapor pressure of 23.80 torr. The value for R is 0.082058 L•atm/mol•K. What is the pressure of H2(g) collected?

0.9516 atm

Put the steps to measure a solid sample on a balance in order: 1. Choose the balance that gives the most precise and accurate results based on the allowable capacity. 2. Carefully brush any spilled reagent away from the balance plate. Ask your instructor for help if necessary. 3. Wait for the reading to stabilize as much as possible before recording the mass. 4. Tare a weighing boat on the balance 5. Place your sample in the weighing boat. 6. If massing crystals or powder, carefully add solid reagent using a spatula until your desired mass is reached. 7. Dispose of your weighing boat as appropriate. 8. If using an analytical balance, close the windows. 9. Remove your weighing boat. 1,2,3,4,5,6,7,8,9 9,8,7,6,5,4,3,2,1 1,4,5,6,8,3,9,2,7 4,5,3,9,2,1,5,6,8,7

1,4,5,6,8,3,9,2,7

Standard Deviation

1. Work out the Mean (the simple average of the numbers) 2. Then for each number: subtract the Mean and square the result 3. Then work out the mean of those squared differences. 4. Take the square root of that

The analysis was performed by dissolving an antacid tablet in 90.00 mL of 0.175 M HCl. The excess acid was back-titrated with exactly 33.15 mL of 0.155 M NaOH. The average weight of a tablet is 1.025 g. The tablet came from a bottle of 175 tablets that cost $4.99. Calculate the mass effectiveness of the antacid.

1.04 x10-2 mol/g

The analysis was performed by dissolving an antacid tablet in 70.00 mL of 0.0957 M HCl. The excess acid was back-titrated with exactly 13.46 mL of 0.1305 M NaOH. The average weight of a tablet is 1.550 g. The tablet came from a bottle of 125 tablets that cost $2.79. If the tablet actually contained 250 mg of CaCO3, calculate the % error (Appendix IB).

1.06%

One possible method for the determination of glucose concentration is based on the formation of a blue-green complex of glucose with o-toluidine in glacial acetic acid. The reaction is as follows: HOCH2(CHOH)4CHO(glucose) + H2N(C6H4)CH3 (o-toluidine)↔ HOCH2(CHOH)4CH=N(C6H4)CH3(blue-green complex) + H2O A stock solution was prepared by dissolving and diluting 0.725 g of glucose (MM=180.156 g/mol) to 100.00 mL with deionized water. A dilution was prepared from the stock solution by treating 40.00mL of the stock solution with o-toluidine and diluting to 100.00mL with deionized water. What is the concentration of the dilution?

1.61x10-2 M

The analysis was performed by dissolving an antacid tablet in 80.00 mL of 0.1225 M HCl. The excess acid was back-titrated with exactly 47.65 mL of 0.123 M NaOH. The average weight of a tablet is 1.102 g. The tablet came from a bottle of 250 tablets that cost $5.99. Calculate the cost effectiveness of the antacid.

1.64x10-3 mol/¢

The bottom of the meniscus of your solution falls halfway between the second and third marking from the 12 mL mark of the nine markings between the 12 mL and 13 mL mark on your buret. How would you report this volume?

12.25 mL

Students performed a procedure similar to Part II of this experiment (Analyzing Juices for Vitamin C Content) as described in the procedure section. Three 10.00 mL samples of juice were titrated with DCP that had a standardized concentration of 1.01x10-3 M. The three titrations took an average of 13.82 mL of DCP. Calculate the mass (in mg) in 50.00 mL of juice. (MM Ascorbic Acid = 176.124 g/mol)

12.3 mg

The analysis was performed by dissolving an antacid tablet in 65.00 mL of 0.0995 M HCl. The excess acid was back-titrated with exactly 12.75 mL of 0.0967 M NaOH. The average weight of a tablet is 1.185 g. The tablet came from a bottle of 200 tablets that cost $5.79. If the tablet actually contained 300 mg of CaCO3, calculate the % error (Exp6)

12.7%

Suppose that you titrate a 100 mg vitamin C tablet and it turns out to contain only 95.5 mg of vitamin C. Further, it took 26.32 mL of DCP solution to reach the end point of that titration. Next, you titrate a sample of orange juice, with the end point occurring after 42.64 mL of DCP solution is added. How many milligrams of vitamin c were in the sample of orange juice?

155 mg

Which of the following serves as the indicator for the titration? Vitamin C 2,6-dichloroindophenol Ascorbic acid Metaphosphoric acid

2,6-dichloroindophenol

A student performed the Separation by Fractional Crystallization experiment described with the following results: Initial mass of sample mixture: 6.359 g, mass of salicylic acid recovered, 0.895 g; mass of CuSO4•5H2O recovered, 4.03 g. The recovered CuSO4•5H2O was then heated for 20 minutes at 120 °C. The mass of the new hydrate was 3.18 g. (The molar mass of H2O = 18.015 g/mol, and the molar mass of CuSO4= 159.61 g/mol) Calculate the value of X in the formula for the new hydrate CuSO4•XH2O.

2.08

The analysis was performed by dissolving an antacid tablet in 75.00 mL of 0.1055 M HCl. The excess acid was back-titrated with exactly 44.97 mL of 0.125 M NaOH. The average weight of a tablet is 1.045 g. The tablet came from a bottle of 125 tablets that cost $3.49. Calculate the moles of HCl neutralized by the tablet.

2.29x10-3 mol

The following data was collected by a student performing the DETERMINING THE SPECIFIC HEAT CAPACITY AND MOLAR HEAT CAPACITY OF COPPER portion of the experiment. A 29.32 g copper coil is removed from boiling water and is immediately immersed in a calorimeter with a constant of 34.8 J/0C. The calorimeter contains 73.12 g of water that is initially at 25.62 0C. The system reaches equilibrium at a temperature of 28.01 0C. What is the molar heat capacity of the copper? (Specific heat of water is 4.184 J/g0C., Molar mass of copper= 65.39 g/mol)

25.2 J/molºC

Place the following steps for lighting a Bunsen burner in their correct order: A striker positioned above the burner can be used to ignite the gas. Check that the gas valve is open on the Bunsen buner. Make sure that the connections are secure at both the gas outlet and at the burner. The tip of the inner core of the flame should be at the base of the glassware. Turn on the gas outlet and listen for the flow of gas. Adjust the gas valve and the air flow regulator on the burner until the flame is about two inches in height.

3,2,5,1,6,4

3.71x10-2 M

3.72x10-3 mol/¢

3.94x10-3 mol

A student used a DCP solution (standardized to 9.98x10-4 M) to analyze a sample of extract from 2.50 g of solid food. The titration required 22.49 mL of DCP. 87.00% of all the ascorbic acid in the food was collected in the extract. (MM Ascorbic Acid = 176.124 g/mol) What mass of food (in grams) would be required to attain the %DV of ascorbic acid (60 mg)?

33.0 g

4.02x10-2 M

The analysis was performed by dissolving an antacid tablet in 83.5 mL of 0.1035 M HCl. The excess acid was back-titrated with exactly 39.75 mL of 0.1025 M NaOH. The average weight of a tablet is 1.095 g. The tablet came from a bottle of 150 tablets that cost $3.99. Calculate the mass effectiveness of the antacid.

4.17x10-3 mol/g

4.42x10-3 mol/g

The analysis was performed by dissolving an antacid tablet in 70.00 mL of 0.0957 M HCl. The excess acid was back-titrated with exactly 13.46 mL of 0.1305 M NaOH. The average weight of a tablet is 1.550 g. The tablet came from a bottle of 125 tablets that cost $2.79. Calculate the moles of HCl neutralized by the tablet.

4.94x10-3 mol

The correct procedure for preparation of a buret for titration of a strong acid with a strong base:

4: once with tap water, once with deionized water, and twice with 5mL of titrant.

How much heat is absorbed by a 115 g sample of water when it is heated from 25.20 ºC to 35.80 ºC? The specific heat of water is 4.184 J/g ºC.

5.10 kJ

One possible method for the determination of glucose concentration is based on the formation of a blue-green complex of glucose with o-toluidine in glacial acetic acid. The reaction is as follows: HOCH2(CHOH)4CHO(glucose) + H2N(C6H4)CH3 (o-toluidine) ↔ HOCH2(CHOH)4CH=N(C6H4)CH3(blue-green complex) + H2O A stock solution was prepared by dissolving and diluting 0.668g of glucose (MM=180.156 g/mol) to 100.00 mL with deionized water. A dilution was prepared from the stock solution by treating 15.00 mL of the stock solution with o-toluidine and diluting to 100.00 mL with deionized water. What is the concentration of the dilution?

5.56x10-3 M

The following data was collected by a student performing the DETERMINING THE MOLAR ENTHALPY OF SOLUTION OF A SALT portion of the experiment. A 2.97 g sample of an aqueous ionic salt with a molar mass of 104.2 g/mol is added to a calorimeter (Ccal= 69.7 J/°C) containing 75.94 g of deionized water. The water is initially at 24.70 ºC, after adding the ionic salt, the system reaches equilibrium at a temperature of 20.31 ºC. What is the molar enthalpy of the salt solution in kJ/mol? (Assume the specific heat of the solution is the same as pure water, 4.184 J/gºC).

61.6 kJ/mol

A student performed the Separation by Fractional Crystallization experiment described with the following results: Initial mass of sample mixture: 10.95 g, mass of salicylic acid recovered, 2.76 g; mass of CuSO4•5H2O recovered, 4.95 g. The recovered CuSO4•5H2O was then heated for 20 minutes at 120 °C. The mass of the new hydrate was 3.61 g. (The molar mass of H2O = 18.015 g/mol, and the molar mass of CuSO4= 159.61 g/mol) Calculate the percent recovered of the total sample.

70.4%

Students performed a procedure similar to Part III of this experiment (Analyzing a Vitamin Supplement for Vitamin C Content) as described in the procedure section. A 1.041 g vitamin C tablet is crushed, treated, and diluted to 100.00 mL in a volumetric flask with deionized water. Three 5.00 mL samples of this solution are titrated with DCP that had a standardized concentration of 1.01x10-3 M. The three titrations took an average of 21.96 mL of DCP. (MM Ascorbic Acid = 176.124 g/mol) Calculate the mass (in mg) in the vitamin C tablet. (MM Ascorbic Acid = 176.124 g/mol)

78.1 mg

8.21x10-2 mol/¢

8.56%

A student based the analysis of Cu(II) in a sample on the formation of the blue complex [Cu(H2O)6]+2. A standard solution was made when 1.825 g of pure copper wire (MM= 63.546 g/mol) was weighed, dissolved in concentrated HNO3, and diluted to 1.00x102 mL. The stock solution was used to make a dilution by mixing 2.00 mL of stock solution with 48.0 mL of deionized water. Colorimetric determination gave that the absorbance of the sample was 0.08795 when the path length of the light through the solution was exactly 1 cm. Calculate the transmittance of the solution.

81.67%

One possible method for the determination of glucose concentration is based on the formation of a blue-green complex of glucose with o-toluidine in glacial acetic acid. The reaction is as follows: HOCH2(CHOH)4CHO(glucose) + H2N(C6H4)CH3 (o-toluidine)↔ HOCH2(CHOH)4CH=N(C6H4)CH3(blue-green complex) + H2O A stock solution was prepared by dissolving and diluting 0.589 g of glucose (MM=180.156 g/mol) to 100.00 mL with deionized water. A dilution was prepared from the stock solution by treating 28.00 mL of the stock solution with o-toluidine and diluting to 100.00 mL with deionized water. What is the concentration of the dilution?

9.15x10-3 M

Students performed Part I of this experiment (Standardizing the DCP solution) as described in the procedure section. The weight of the reagent grade AA that was 40.21 mg. The AA was diluted to 50.00mL in a volumetric flask. Three 5.00 mL portions of the AA solution were titrated with 22.64, 24.47, and 23.18 mL of DCP respectively. Calculate the average molarity of the DCP solution and the standard deviation associated with these measurements. Check your two answers. (MM Ascorbic Acid = 176.124 g/mol)

9.75x10-4 M 3.86x10-5 M

Which of the following would be an appropriate graduated cylinder in which to measure the volume of an irregularly shaped object with a diameter of 1.75 cm?

A 50 mL graduated cylinder with a diameter of 2 cm

What is true about a meniscus? A meniscus is the curvature of the upper surface of a liquid in glassware due to tension forces acting between the glass and the liquid. A meniscus for aqueous solutions is always convex. We always read the bottom of a meniscus. All of the above.

A meniscus is the curvature of the upper surface of a liquid in glassware due to tension forces acting between the glass and the liquid.

What is a state function?

A quantity dependent only on its current state but not how it got there.

The solvent front of your chromatogram should be marked:

After the solvent front has stopped moving, but before it has dried.

An analytical balance: Have a smaller total capacity than top-loading balances Have greater precision than top-loading balances. Are in a glass enclosure to minimize the effect of air movement. All of the above None of the above

All of the Above

What special precautions need to be observed when handling the 2.5M NH3 being used in the Beer's Law experiment? Check all that apply.

Ammonia will be dispensed in the hoods ONLY Ammonia should not be added to an EMPTY volumetric flask

Systematic error occurs when (Select all that apply) An instrument is consistently yielding a high or low value for a result. A lab technician is erroneously making the same measuring mistake. A system failure occurs in computer analysis

An instrument is consistently yielding a high or low value for a result. A lab technician is erroneously making the same measuring mistake.

Why don't we titrate an antacid tablet directly with a standardized acid solution? Check all that apply. Antacids are not very soluble in acidic solutions. Antacids are not very soluble in water. Antacids are weak bases. Antacids exhibit resistance to pH change while being titrated.

Antacids are not very soluble in water. Antacids are weak bases. Antacids exhibit resistance to pH change while being titrated.

Required attire in the lab includes:

Approved Goggles Non-latex gloves Closed-toe shoes that do not leave the top of the foot exposed Long Pants Lab Coat

Why would you expect the solubility of most solids to increase as the temperature of the solvent increases?

At elevated temperature, there is more kinetic energy available to break the intermolecular forcers and dissolve the solute.

The correct procedure for transferring liquid with a volumetric pipet. First, rinse with tap water and do a second rinse with deionized water. If using an atomizer bulb: Compress the rubber bulb and place it carefully over the upper end of the pipet. The bulb only needs to cover the end of the pipet to create an airtight seal, there is no need to push the pipet farther into the bulb. You may want to lubricate the hole of the rubber bulb with a drop of deionized water. If using a rolling pipet top: Press the proper sized pipet top tightly onto the end of the pipet in order to create an airtight seal. Place the tip of the pipet in the liquid and draw the liquid into the pipet and above the calibration line. Keep the pipet tip submerged to avoid air bubble entry. Be careful not to draw the liquid into the bulb. Dispose of this first amount of liquid into a waste beaker. Once again, draw in the liquid to be measured above the calibration line in the pipet. If using an atomizer bulb: remove the bulb while simultaneously covering the tip of the pipet with your finger. Now allow the liquid level to drop to the required level by slowly allowing air to enter the pipet by a controlled lifting of the finger that is covering the end of the pipet. If using a rolling pipet top, there is no need to remove the top. Push the side button to allow your pipet to drain. When the liquid level is at the correct place, move the pipet tip to the glassware where you want the liquid delivered and release your finger. Allow the pipet to drain into the container and touch off any last drop on the pipet side of the glassware. There may be some liquid remaining in the pipet tip. Do no blow this remaining liquid from the pipet. The pipet was calibrated to deliver the correct volume with this liquid remaining. NEVER allow the liquid to enter the pipet top (atomizer bulb or rolling). What is the major difference between the atomizer bulb and a rolling pipet top:

Atomizer bulbs should be loosely attached to the pipet to facilitate their removal when draining the pipet, where rolling pipet tops should be more tightly attached to the pipet and don't have to be removed to drain the pipet.

What are the advantages to using back titration to analyze an antacid? Check all that apply. Back titration will allow us to perform a strong acid/strong base titration. The base of the antacid will be completely neutralized. We will not have to heat the solution. Strong Acid/Strong Base titrations are simpler to analyze than strong acid/weak base titrations.

Back titration will allow us to perform a strong acid/strong base titration. The base of the antacid will be completely neutralized. Strong Acid/Strong Base titrations are simpler to analyze than strong acid/weak base titrations.

Once we form the visible-light absorbing species in this experiment, what color will the solution appear to be?

Blue

What is the difference between mass % and density?

Density is mass/volume, where mass % is (mass solute/mass solution) * (100)

Rf calculation

Distance test solution traveled/Distance solvent traveled Solvent is most likely water LESS THAN ONE

Which of the following is not considered volumetric glassware? Erlenmeyer flasks Volumetric flasks Burets Pipets

Erlenmeyer flasks

Graduated cylinders are used for the most precise volumetric measurements of liquids.

False (Volumetric flasks are most precise)

Gloves can be disposed of in the regular trash

False; must be disposed of as hazardous waste

If you dissolve a certain ionic salt in water, the solution temperature rises. What is happening in thermodynamic terms?

Heat is leaving the system and the reaction is exothermic.

What type of chromatography would be best for separating a mixture of starch and cellulose?

High Performance Liquid Chromatography

When is the best time to clean equipment and tools in the lab?

Immediately after use

Deionized water: Should be used generously when cleaning glassware. Is considered a reagent and should be dispensed as needed only from a wash bottle when rinsing glassware. Is plain tap water.

Is considered a reagent and should be dispensed as needed only from a wash bottle when rinsing glassware.

Why do we set the colorimeter to 635 nm?

It is the closest to the peak wavelength of the red/orange light that is absorbed by the species

What role does the metaphosphoric acid play in the vitamin C analysis?

It precipitates proteins present in foods

What role does the pH 3 buffer play in the vitamin C analysis? (Select all that apply) It precipitates proteins present in foods It prevents side reactions with sulfhydryl compounds and phenols It prevents the decomposition of vitamin c

It prevents side reactions with sulfhydryl compounds and phenols It prevents the decomposition of vitamin c

What is significant about the sulfuric acid used in the Qualitative Analysis Experiment?

It's a more concentrated chemical than we usually handle in lab, and needs to be handled with extra care: drops will be added to your reaction mixture directly from a dropper bottle. You will NOT pour this concentrated chemical from its container into a beaker. (correct)

A special receptacle for the disposal of gloves, broken glass and other solid waste is: A) Located at several places throughout the lab (correct) B) Located in the hall C) Located at the White Drum D) Does not exist. These may be discarded in the trash.

Located at several places throughout the lab

Why are we cautious in the handling of acids and bases, no matter what their concentration?

No matter their concentration, acids and bases can be corrosive, toxic and irritating.

We are given an unknown antacid pill and through the procedure in this lab we determine its cost effectiveness to be 5.0x10-1 mole of acid/$. Can we also determine the number of moles of base in the pill? Yes, we simply write a balanced chemical equation No, because antacid tablets are a formulation of unknown compounds Sometimes it's possible with pure antacids None are correct

No, because antacid tablets are a formulation of unknown compounds

A set of dilutions ranging in concentration from 1x10-2 M to 2x10-2 M are used to prepare a Beer's Law plot. Transmittances of the dilutions range from 12% to 88%. Could this plot be used to determine the concentration of a sample that had a concentration of 1.0x10-3 M? Yes, simply extend the Beer's Law plot. No, the solution is too concentrated and would have a %T over 90% where Beer's Law does not apply. No, the solution is too concentrated and would have a %T under 10% where Beer's Law does not apply. No, the solution is too dilute and would have a %T over 90% where Beer's Law does not apply. No, the solution is too dilute and would have a %T under 10% where Beer's Law does not apply.

No, the solution is too dilute and would have a %T over 90% where Beer's Law does not apply.

The voltage produced by the colorimeter is __________ to the absorbance of the sample and ____________ to the light intensity. Directly proportional, indirectly proportional Directly proportional, directly proportional Indirectly proportional, indirectly proportional Indirectly proportional, directly proportional None of the above

None of the above

Explain the term parallax in the context of reading a meniscus and how you would avoid any error that might be introduced by parallax?

Parallax error is the apparent displacement of an object as seen from two different viewpoints that are not in line with the object. The meniscus must consistently be read at eye level.

A proper Beer's Law plot is

Shows a linear relationship when plotting Absorbance vs. Concentration

Cuvets have two types of surfaces: one intended to transmit light and one not intended to transmit light from the LED. T/F

You need 10.0 mL of a certain chemical. What's the best approach?

Take a 50 mL or 150 mL beaker to the hood and carefully pour slightly more than 10 mL of solution from the stock bottle, then take the solution back to your desk and measure precisely 10 mL in your 10 mL graduated cylinder.

What is the definition of the molar enthalpy of neutralization?

The heat released in the neutralization of one mole of acid or base at constant pressure.

A scientist does two sets of experiments with three trials each to determine the density of an unknown solution. The three trials for the first experiment have a standard deviation of 0.0980 g/mL. The three trials for the second experiment have a standard deviation of 0.0137 g/mL. What can we infer?

The measurements from the second experiment were more precise.

Suppose that you run a chemical reaction in a constant-pressure calorimeter and you observe the temperature of the contents of the calorimeter decrease. What is the most likely reason? endo/exo

The reaction is endothermic.

How will we know when we have reached the end-point in our titration?

The solution will change color

What would be the consequences of the following scenario and what effect would it have on your experimental results? The beakers containing the solvents were not covered while running the experiment.

The solvent could evaporate. If the solvent evaporated before the experiment was complete, we could not accurately determine Rf values.

The Dyes Blue 1 and Green 3 have very similar Rf's in most solvents. Why do you think this is?

The structures of the two dyes are nearly identical, except for the substituent on one aromatic ring.

What is the role of sodium hydroxide in this experiment 12?

To determine the amount of excess hydrochloric acid remaining after the reaction with magnesium

In this experiment, you will employ the ammonia, NH3, and the thiocyanate ion, SCN-, for much the same purpose. The common purpose is: To form a complex. As an acid As an acid-base indicator as a metal cation.

To form a complex.

Why do we need to filter samples of juice and food products before titration in this experiment?

To remove pulp and other solids from the solution

What would be the consequences of the following scenario and what effect would it have on your experimental results? A student used a dropper rather than a toothpick to put a small drop of each dye on the chromatography paper.

Too much dye would be spotted, causing large spots that would spread. The chromatogram would be impossible to analyze properly.

Solutions will show deviations from Beer's Law when they: (Select all that apply) Are too complex Transmit more than 90% of incident light Transmit less than 10% of incident light Absorb more than 10% of incident light Absorb less than 90% of incident light

Transmit more than 90% of incident light Transmit less than 10% of incident light

How do we compensate for absorbance of light by the cuvet walls, the solvent, and the solutes other than the complex ion.

We calibrate with cuvet, solvent, and other solutes present

What do we mean by "waste minimization?"

We try to use as little reagents as possible during the experiment. We take only the amounts of reagents necessary to complete the experiment. We dispose of waste in proper containers. We do not return excess waste to the reagent bottles.

What would be the consequences of the following scenario and what effect would it have on your experimental results? The chromatogram was removed from the solvent after the solvent front had reached the top of the chromatogram paper

We would be unable to determine how far the solvent front traveled, and therefore could not determine the Rf for the components.

Which is the final step when cleaning a piece of volumetric glassware prior to making a volumetric measurement? Rinse with deionized water. Clean using a brush and approved laboratory glassware cleaner. Rinse with tap water. Wet the surfaces of the glassware with the liquid being measured.

Wet the surfaces of the glassware with the liquid being measured.

When do you remove a chromatogram from its solvent?

When the solvent front is 2 cm from the top of the chromatogram.

Is this the correct procedure for cleaning glassware prior to making a measurement: First, Clean with approved laboratory glassware cleaner and a brush. Second, Rinse with tap water. Third, Rinse with deionized water from your wash bottle. Dispose of these rinses in your waste beaker.

Yes

Is this the correct procedure for cleaning volumetric glassware prior to making a measurement: First, Rinse with tap water. Second, Rinse with deionized water from your wash bottle. Finally, if the glassware is volumetric, rinse once (or preferably twice) with the solution you are going to be measuring. Dispose of these rinses in your waste beaker.

Yes

Would you expect a large piece of titanium oxide to have the same density as a small piece? yes/no intensive/extensive

NYU Chem Lab Final

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