CHEM LAB FINAL

he following data was collected by a student performing the DETERMINING THE MOLAR ENTHALPY OF NEUTRALIZATION portion of the experiment. 50.00 mL of a 0.250 M acid is combined with 50.00 mL of 0.255 M NaOH. Before the reaction, the acid and base are at a temperature of 24.92 °C. After mixing, the neutralized solution reaches a maximum temperature of 26.50 °C in a calorimeter (Ccal=58.4 J/°C). The neutralized solution has a specific heat of 3.89 J/g°C and a density of 1.04 g/mL. What is the molar enthalpy of neutralization in kJ/mol?

-58.5 kJ/mol

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 moles of CuSO4 in the new hydrate (CuSO4•XH2O).

0.0161 mol

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 moles of water in the new hydrate (CuSO4•XH2O).

0.0335 mol

The experiment described in the procedure was performed using a sample of Calcium with HCl(aq). The lab conditions were 27.00 °C, and 747.0 torr barometric pressure. 96.55 mg of Calcium (MM: 40.08 g/mol) was reacted with 25.00 mL of 0.750M HCl(aq). 63.049 g of water was collected when the reaction was complete, and it required 27.95 mL of 0.500M NaOH(aq) to titrate the reaction mixture. Water at 27.00 °C has a density of 0.9965 g/cm3, and a vapor pressure of 26.80 torr. The value for R is 0.082058 L•atm/mol•K. What is the volume of H2(g) generated?

0.06327 L

What concentration of hydrochloric acid will we be using in the Intro to Lab Quest© Experiment?

0.2 M

A student performed the Separation by Fractional Crystallization experiment described with the following results: Initial mass of sample mixture: 8.35 g, mass of salicylic acid recovered, 2.38 g; mass of CuSO4•5H2O recovered, 5.09 g. The recovered CuSO4•5H2O was then heated for 20 minutes at 120 °C. The mass of the new hydrate was 3.62 g. (The molar mass of H2O = 18.015 g/mol, and the molar mass of CuSO4= 159.61 g/mol) Calculate the mass of water in the new hydrate (CuSO4•XH2O).

0.366 g

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 32.54 g copper coil is removed from boiling water and is immediately immersed in a calorimeter with a constant of 71.1 J/ºC. The calorimeter contains 74.61 g of water that is initially at 25.78 ºC. The system reaches equilibrium at a temperature of 28.25 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)

0.407 J/gºC

Using a metric ruler subdivided into mm, refer to Figure 3.4 on page 36 of your lab manual. Calculate the Rf for component B.

0.705

A student performed the Separation by Fractional Crystallization experiment described with the following results: Initial mass of sample mixture: 4.958 g, mass of salicylic acid recovered, 0.586 g; mass of CuSO4•5H2O recovered, 3.12 g. The recovered CuSO4•5H2O was then heated for 20 minutes at 120 °C. The mass of the new hydrate was 2.17 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.

0.780

The experiment described in the procedure was performed using a sample of Calcium with HCl(aq). The lab conditions were 27.00 °C, and 747.0 torr barometric pressure. 96.55 mg of Calcium (MM: 40.08 g/mol) was reacted with 25.00 mL of 0.750 M HCl(aq). 63.049 g of water was collected when the reaction was complete, and it required 27.95 mL of 0.500 M NaOH(aq) to titrate the reaction mixture. Water at 27.00 °C has a density of 0.9965 g/cm3, and a vapor pressure of 26.80 torr. The value for R is 0.082058 L•atm/mol•K. What is the pressure of H2(g) collected?

0.9476 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.

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

The experiment described in the procedure was performed using a sample of Calcium with HCl(aq). The lab conditions were 27.00 0C, and 747.0 torr barometric pressure. 96.55 mg of Calcium (MM: 40.08 g/mol) was reacted with 25.00 mL of 0.750 M HCl(aq). 63.049 g of water was collected when the reaction was complete, and it required 27.95 mL of 0.500 M NaOH(aq) to titrate the reaction mixture. Water at 27.00 0C has a density of 0.9965 g/cm3, and a vapor pressure of 26.80 torr. The value for R is 0.082058 L•atm/mol•K. What is the ratio of moles H2 gas generated to moles of metal reacting?

1.00:1

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 mass of water lost from the hydrate during heating.

1.34 g

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 mass of water in the recovered hydrate before heating (CuSO4•5H2O).

1.45 g

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 3.00 mL of the stock solution with o-toluidine and diluting to 100.00 mL with deionized water. What is the concentration of the dilution?

1.46x10^-3 M

A block of an unknown metal has a mass of 155.6 kg and a volume of 0.1018 cubic meters. Calculate its density in g/mL

1.528 g/mL

Using a metric ruler subdivided into mm, refer to Figure 3.4 on page 36 of your lab manual. Measure the distance Spot C has moved.

1.85 cm

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. What is the concentration of the dilution?

1.85x10^-3 M

A block of an unknown metal has a mass of 227.8 kg and a volume of 0.1189 cubic meters. Calculate its density in g/L.

1.916x10^3 g/L

A block of an unknown metal has a mass of 227.8 kg and a volume of 0.1189 cubic meters. Calculate its density in kg/m3.

1.916x10^3 kg/m^3

e bottom of the meniscus of your solution falls 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. The bottom of the meniscus is a little closer to the second mark than the third. How would you report this volume?

12.22 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

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 1.043 g vitamin C tablet is crushed, treated, and diluted to 100.00 mL in a volumetric flask with deionized water. Three 5.00mL samples of this solution are titrated with DCP that had a standardized concentration of 9.93x10-4 M. The three titrations took an average of 35.52 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)

124 mg

Which of the following serves as the indicator for the titration? (Exp 9. Vitamin C Analysis)

2,6-dichloroindophenol

The experiment described in the procedure was performed using a sample of Calcium with HCl(aq). The lab conditions were 27.00 °C, and 747.0 torr barometric pressure. 96.55 mg of Calcium (MM: 40.08 g/mol) was reacted with 25.00 mL of 0.750 M HCl(aq). 63.049 g of water was collected when the reaction was complete, and it required 27.95 mL of 0.500 M NaOH(aq) to titrate the reaction mixture. Water at 27.00 °C has a density of 0.9965 g/cm3, and a vapor pressure of 26.80 torr. The value for R is 0.082058 L•atm/mol•K. How many moles of H2 gas are generated?

2.434 x10^-3 mol

If a 26.366 g sample of water has a density of 0.9982 g/mL at 25 °C, what would be its volume in L?

2.641x10^-2

What would the mass of 0.02432 L of water be at 25 °C? ( the density of water at 25 °C is 0.9982 g/mL)

24.28 g

A student performed the Separation by Fractional Crystallization experiment described with the following results: Initial mass of sample mixture: 7.38 g, mass of salicylic acid recovered, 1.76 g; mass of CuSO4•5H2O recovered, 4.23 g. The recovered CuSO4•5H2O was then heated for 20 minutes at 120 °C. The mass of the new hydrate was 3.15 g. (The molar mass of H2O = 18.015 g/mol, and the molar mass of CuSO4= 159.61 g/mol) Calculate the mass percent of salicylic acid in the recovered sample.

29.4%

Place the following steps for lighting a Bunsen burner in their correct order: 1. A striker positioned above the burner can be used to ignite the gas. 2. Check that the gas valve is open on the Bunsen buner. 3. Make sure that the connections are secure at both the gas outlet and at the burner. 4. The tip of the inner core of the flame should be at the base of the glassware. 5. Turn on the gas outlet and listen for the flow of gas. 6. 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

Place the following steps for lighting a Bunsen burner in their correct order: 1. A striker positioned above the burner can be used to ignite the gas. 2. Check that the gas valve is open on the Bunsen burner. 3. Make sure that the connections are secure at both the gas outlet and at the burner. 4. The tip of the inner core of the flame should be at the base of the glassware. 5. Turn on the gas outlet and listen for the flow of gas. 6. 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

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. How many times should you rinse a pipet before transferring liquid?

3- once with tap water, once with deionized water, and once (or twice) with the solution being transferred.

An analysis of generic antacid tablets labeled to contain 750 mg of CaCO3(MM= 100.09 g/mol) per tablet of active ingredient was performed. The analysis was performed by dissolving a 0.985 g sample of the 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 cost effectiveness of the antacid.

3.87x10^-3 mol/¢

How much heat is absorbed by a 122 g sample of water when it is heated from 28.20 ºC to 35.80 ºC? The specific heat of water is 4.184 J/g ºC.

3.88 kJ

An analysis of generic antacid tablets labeled to contain 350 mg of CaCO3 (MM= 100.09 g/mol) per tablet of active ingredient was performed. The analysis was performed by dissolving a 0.667 g sample of the 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 moles of HCl neutralized by the sample.

3.94x10^-3 mol

A block of an unknown metal has a mass of 227.8 kg and a volume of 0.1189 cubic meters. If the object were a sphere, what would be its radius? (The value for pi ≈ 3.14159)

30.50 cm

An analysis of generic antacid tablets labeled to contain 350 mg of CaCO3 (MM= 100.09 g/mol) per tablet of active ingredient was performed. The analysis was performed by dissolving a 0.667 g sample of the 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 actual mg per tablet of CaCO3 in the generic antacid.

326 mg

An analysis of generic antacid tablets labeled to contain 500 mg of CaCO3 (MM= 100.09 g/mol) per tablet of active ingredient was performed. The analysis was performed by dissolving a 0.750 g sample of the 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 % relative error for the mg CaCO3 tablet found compared to the labeled content.

33.2%

A block of an unknown metal has a mass of 155.6 kg and a volume of 0.1018 cubic meters. If the object were a cube, what would be the dimension of one of its sides?

46.69 cm

The correct procedure for preparation of a buret for titration of a strong acid with a strong base: 1. First clean the buret with tap water and a buret brush (if available). 2. Rinse the interior of the buret with tap water. 3. Rinse the interior of the buret with deionized water. 4. Rinse the interior of the buret with about 5mL of your titrant, dispose of this aliquot in your waste beaker. To properly wet the inside surfaces, tip the buret on its side while holding it in your hand. Be careful not to spill the solution (you can use parafilm to cover the open end of the buret). Make sure the solution comes into contact with every surface in the interior of the buret by rotating the buret. Drain the rinse solution through the stopcock into the waste beaker. 5. Rinse the interior of the buret with about 5mL of your titrant as above. Also dispose of this aliquot in your waste beaker. 6. Check the stopcock for leaks. Make sure it is not loose. 7. When filling the buret, do so at eye level and always use a funnel. You may need to unclip the buret from the stand when filling or refilling. 8. Make sure the stopcock is closed, and that you not pouring a chemical above eye level. Use a funnel and fill the buret above the 0.0 mark with titrant. Be careful that you do not overfill the buret. 9. Clip the buret to the stand, making sure it is perfectly vertical. Drain the buret carefully through the stopcock until the buret reads 0.00mL. 10. Place a beaker underneath the full buret in case the stopcock comes loose. Always keep a beaker underneath a buret that has titrant in it. How many times should you rinse your buret before you fill it to the calibration mark with titrant?

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

A student performed the Separation by Fractional Crystallization experiment described with the following results: Initial mass of sample mixture: 9.58 g, mass of salicylic acid recovered, 4.35 g; mass of CuSO4•5H2O recovered, 4.68 g. The recovered CuSO4•5H2O was then heated for 20 minutes at 120 °C. The mass of the new hydrate was 3.83 g. (The molar mass of H2O = 18.015 g/mol, and the molar mass of CuSO4= 159.61 g/mol) Calculate the mass percent of copper(II) sulfate pentahydrate in the recovered sample.

51.8%

How many mixtures of FD&C Dyes will you be spotting on Chromatogram

6

An analysis of generic antacid tablets labeled to contain 500 mg of CaCO3 (MM= 100.09 g/mol) per tablet of active ingredient was performed. The analysis was performed by dissolving a 0.750 g sample of the 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.

6.09x10-3 mol/g

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. How many moles of HCl(aq) are consumed in the reaction with the metal?

6.73 x10^-3 mol

22.1.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

he following data was collected by a student performing the DETERMINING THE CALORIMETER CONSTANT portion of the experiment. 50.00 g of hot water is mixed with 50.00 g of cold water Interpolating back to the time of mixing shows that the temperature of the hot water was 46.21 ºC, the temperature of the cold water was 24.56 ºC, and the temperature of the mixture was 33.95 ºC. The specific heat of water is 4.184 J/g ºC. What is the calorimeter constant, Ccal?

63.9 J/ºC

Suppose that you titrate a 3 g sample of orange juice 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 the titration. Next, you boil a 3 g sample of orange juice for 15 min and then titrate it, with the end point occurring after only 8.77 mL of DCP solution is added. What percentage of the vitamin C was destroyed in the boiling?

66.7%

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%

An analysis of generic antacid tablets labeled to contain 650 mg of CaCO3 (MM= 100.09 g/mol) per tablet of active ingredient was performed. The analysis was performed by dissolving a 0.605 g sample of the 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. Calculate the moles of HCl neutralized by 1.00 g of the antacid tablet.

8.65x10^-3 mol

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 45.97 mg. The AA was diluted to 50.00 mL in a volumetric flask. Three 5.00 mL portions of the AA solution were titrated with 27.13, 25.23, and 26.63 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)

9.92x10-4 M

An 11.65 g sample is added to 105.1 mL of pure water (density of pure water @25 °C is 0.9982 g/mL). What is the mass % of the NaCl solution?

9.995%

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 leuco dye?

A DCP reduction product

What will increase the absorbance of a sample?

A longer path length

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.

Systematic error occurs when

A. An instrument is consistently yielding a high or low value for a result. B. 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.

A. Antacids are not very soluble in water. (correct) B. Antacids are weak bases. (correct) C. Antacids exhibit resistance to pH change while being titrated. (correct)

The solvent front of your chromatogram should be marked

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

What is dehydroascorbic acid?

An ascorbic acid oxidation product

When cleaning volumetric glassware

As a final step before measuring, wet the inside surfaces with the liquid being measured.

What plays the role of the reducing agent in our reaction? (Exp 9. Vitamin C Analysis)

Ascorbic acid

Which species is oxidized in our reaction?

Ascorbic acid

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. 1.First clean and rinse your pipet with approved laboratory glassware cleaner, rinse with tab water and do a second rinse with deionized water. 2.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. 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. 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. 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. 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. Strong Acid/Strong Base titrations are simpler to analyze than strong acid/weak base titrations.

According to the procedure in this experiment, you will dissolve an antacid tablet into a specific amount of hydrochloric acid solution, and then add an acid-base indicator. After the titration, the indicator should show the resulting solution is:

Basic Neutral

What causes the seven approved FD&C dyes to be brightly colored?

C. The dyes all have long carbon structures with alternating single and double bonds between the carbons. D. The dyes are all conjugated systems. c&d (correct)

A student has a solution containing a mixture of metal cations: Cu+2, Cr+2, and Fe+3, each a solution with NO3- anion. Adding a concentrated solution of NH4OH(aq) caused the precipitation of Cr+2 and Fe+3 as insoluble hydroxides. The Cu+2 remained in solution and forms the complex ion Cu(NH3)4+2. Which balanced molecular equations represent each of these reactions? Check all that apply.

Cu(NO3)2(aq) + 4NH4OH(aq) → Cu(NH3)4+2(aq) + 2NO3-(aq) + 4H2O(l) Cr(NO3)2(aq) + 2NH4OH(aq) → 2NH4NO3(aq) + Cr(OH)2(s) Fe(NO3)3(aq) + 3NH4OH(aq) → 3NH4NO3(aq) + Fe(OH)3(s)

A student has a solution containing a mixture of metal cations: Cu+2, Cr+2, and Fe+3, each a solution with NO3- anion. Adding a concentrated solution of NH4OH(aq) caused the precipitation of Cr+2 and Fe+3 as insoluble hydroxides. The Cu+2 remained in solution and forms the complex ion Cu(NH3)4+2. Which balanced net ionic equations represent each of these reactions? Check all that apply.

Cu+2(aq) + 4NH4+(aq) +4OH-(aq) → Cu(NH3)4+2(aq) + 4H2O(l) (correct) Cr+2(aq) + 2OH-(aq) → Cr(OH)2(s) Fe+3(aq) + 3OH-(aq) → Fe(OH)3(s)

What plays the role of the oxidizing agent in our reaction? (Exp. 9 Vitamin C Analysis)

DCP

What is the difference between mass % and density?

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

What graph will we be plotting in this experiment (exp 2)

Density vs. % Salt by Mass in Water

How will we measure the volume of hydrogen gas generated?

Determining the volume of water displaced by hydrogen gas

Which of the following is not considered volumetric glassware?

Erlenmeyer flasks

The students working at lab bench F13 on the 20th of March want to save their second graph, under what file name should they save it?

F13_3-20_2

In error analysis, precision and accuracy are a measure of the same experimental phenomenon.

False

Which is a separation technique that takes advantage of boiling point differences?

Fractional Distillation

What type of chromatography would be best for separating a mixture of pentane and hexane

Gas-liquid chromatography

Top Loading Balances:

Have a lower precision than analytical balances.

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

Heat is entering the surroundings and the reaction is exothermic.

Accuracy is a measure of:

How close the measurement is the actual measurement

What hazards are associated with the 0.1% sodium chloride solution being used in the Chromatography Experiment

Irritant

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?

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

What is a fume hood?

Laboratory devices that allow us to experiment with volatile or noxious chemicals while isolating their vapors from the laboratory

In a graduated cylinder, what part of the meniscus should be used to indicate the volume?

Measure either the top of the meniscus if the liquid forms a convex surface, or the bottom of the meniscus if the liquid forms a concave surface

Which one of the following bases will be used as the titrant?

NaOH (aq)

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?

No, because antacid tablets are a formulation of unknown compounds

Why do we want the ends to overlap when we roll up our chromatograms

None of the above

1.1. The correct procedure for preparation of a buret for titration of a strong acid with a strong base: 1. First clean the buret with tap water and a buret brush (if available). 2. Rinse the interior of the buret with tap water. 3. Rinse the interior of the buret with deionized water. 4. Rinse the interior of the buret with about 5mL of your titrant, dispose of this aliquot in your waste beaker. To properly wet the inside surfaces, tip the buret on its side while holding it in your hand. Be careful not to spill the solution (you can use parafilm to cover the open end of the buret). Make sure the solution comes into contact with every surface in the interior of the buret by rotating the buret. Drain the rinse solution through the stopcock into the waste beaker. 5. Rinse the interior of the buret with about 5mL of your titrant as above. Also dispose of this aliquot in your waste beaker. 6. Check the stopcock for leaks. Make sure it is not loose. 7. When filling the buret, do so at eye level and always use a funnel. You may need to unclip the buret from the stand when filling or refilling. 8. Make sure the stopcock is closed, and that you not pouring a chemical above eye level. Use a funnel and fill the buret above the 0.0 mark with titrant. Be careful that you do not overfill the buret. 9. Clip the buret to the stand, making sure it is perfectly vertical. Drain the buret carefully through the stopcock until the buret reads 0.00mL. 10. Place a beaker underneath the full buret in case the stopcock comes loose. Always keep a beaker underneath a buret that has titrant in it. Which is incorrect?

None of the above are incorrect.

The correct procedure for using a volumetric flask: 1. First clean and rinse your flask with tap water and do a second rinse with deionized water. 2. Using a properly sized volumetric pipet, deliver a measured amount of the standardized reagent solution to the volumetric flask. 3. Fill the flask to the graduation line with your solvent (it is helpful to use a disposable pipet to add the last few drops. If the solution is aqueous, the bottom of the meniscus should be at the graduation line. 4. If you overshoot the graduation line, you will need to remake your dilution. 5. Covering the top of the flask with a stopper or a piece of parafilm (and NOT your glove), mix the solution by inverting the flask several times. What do you use to cover your volumetric flask when mixing?

Parafilm A glass stopper

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.

Which parts of the experiment require a mortar and pestle?

Part III- Analyzing a Vitamin Supplement for Vitamin C content

What physical property of the dyes are we exploiting in order to separate the components of each dye?

Polarity

How would you determine the number of significant figures when reading the volume of an aqueous solution in a graduated cylinder

Read the bottom of the meniscus at eye level; report your data to the nearest calibration mark and add an estimated digit

In preparation for a separation by filtration, we add a solvent to extract one component of a mixture, leaving the others as solids. Which one of the following is an acceptable term for the liquid portion?

Supernatant

What is the calorimeter constant?

The amount of heat required to change the temperature of a constant-pressure calorimeter by 1 oC.

What is the definition of specific heat capacity?

The amount of heat required to change the temperature of one gram of a substance by 1 oC.

What is the definition of molar heat capacity?

The amount of heat required to change the temperature of one mole of a substance by 1 oC.

If you combine an aqueous solution of your unknown mixture of cations with a reagent that should produce a precipitate with one of the cations involved in the experiment and you do not observe the formation of a precipitate, what should you conclude?

The cation under consideration is not present in the unknown mixture

If you combine an aqueous solution of your unknown mixture of cations with a reagent that should produce a precipitate with one of the cations involved in the experiment and you observe the formation of a precipitate, what should you conclude?

The cation under consideration is present in the unknown mixture.

n the redox titration of vitamin C by 2,6-dichloroindophenol, how will we recognize the end point?

The excess 2,6-dichloroindophenol will turn the solution pink

What would be the consequences of the following scenario and what effect would it have on your experimental results? The origin line was marked with pen, and not pencil.

The marks on the origin line would separate and elute, mixing with the dyes. We could not accurately determine Rf values

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 0.0980g/mL. The three trials for the second experiment have a standard deviation of 0.0137g/mL. What can we infer?

The measurements from the second experiment were more precise

There are four pressures with which we must concern ourselves in this experiment. Which one of the following is related stoichiometrically to the amount of metal used?

The partial pressure of hydrogen in the flask

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

The reaction is exothermic.

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

The solution will change color

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

In this experiment, we will be performing a titration with a buret. Place the steps in order. 1. Record the pH when 0.0 mL of NaOH has been added to your beaker containing 25 mL of HCl and 25 mL of deionized water. 2. Record the pH of your partially neutralized HCl solution when 5.00 mL of NaOH has been added from the buret. 3. Record the pH of your partially neutralized HCl solution when 10.00mL, 15.00mL and 20.00mL of NaOH has been added. 4. Record the pH of your partially neutralized HCl solution when 21.00 mL, 22.00 mL, 23.00 mL and 24.00 mL of NaOH has been added. 5. Add NaOH one drop at a time until a pH of 7.00 has been reached, then record the volume of NaOH added from the buret. 6. Record the pH of your basic HCl-NaOH solution when 26.00 mL, 27.00 mL, 28.00 mL, 29.00 mL and 30.00 mL of NaOH has been added. 7. Record the pH of your basic HCl-NaOH solution when 35.00 mL, 40.00 mL, 45.00mL and 50.00 mL of NaOH has been added from your 50mL buret.

They're in order already, and we're just trying to point out that students often repeat this part of the experiment because they don't read through the instructions first.

What is the role of sodium hydroxide in this experiment? (EXP 12. Measuring Gas Evolution)

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

Why do we warm the mixture after adding water to it?

To increase the rate at which the entire mixture dissolves

Why do we add ethanol to our solution? Exp 13

To lower the solubility of copper(II) sulfate pentahydrate

How should you report your reading from the buret?

To the nearest calibration mark, then add one estimated digit

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.

According to the procedure which of the following graphs in our experiment will have a linear relationship? (exp 3)

Volume vs. 1/Pressure

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?

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

Refer to Figure 3.4 on page 36 of your lab manual. Was this a good choice of solvent for the separation?

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

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 would you do if there was a tiny bit of liquid left inside the end of the pipet after the pipet has drained:

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

When preparing acidic solutions, always add

acid to water

An MSDS includes what information about a chemical

all of the above

Which of the following could not be a unit for density:

g/m

Which of the following are extensive properties? Check all that apply

mass volume