Determination of The Percentage of Acetic Acid in Vinegar Lab Report

Experiment – Determination of the Percentage of Acetic Acid in Vinegar

Directions: To complete the experiment, read the laboratory experiment in the manual, watch the video below, and complete the data table below.

The experimental report must be submitted to the appropriate Blackboard assignment folder.

Reading Assignment: Determination of the Percentage of Acetic Acid in Vinegar

 

Experimental Videos: Determination of the Percentage of Acetic Acid in Vinegar

 

https://youtu.be/YqfvRBJ-iPg

https://youtu.be/9pS7Q4MQCYI

https://youtu.be/d1XTOsnNlgg

 

 

 

Simulated Data:

Complete the data table. Remember Significant figures

The molar mass of acetic acid is 60.05g/mol.

Assume that the density of vinegar is equal to that of water (1g/mL)

 

Trial 1

Trial 2

Trial 3

Molarity of NaOH (M)

0.700

0.700

0.700

Volume of vinegar used (mL)

25.0

25.0

25.0

Initial buret reading (mL)

15.65

0.00

0.00

Final buret reading (mL)

46.70

31.70

32.30

Volume of NaOH used (mL)

 

 

 

Volume of NaOH used (L)

 

 

 

Moles of NaOH used (mol)

 

 

 

Moles of acetic acid in sample (mol)

 

 

 

Mass of solution (g)

 

 

 

Mass of acetic acid (g)

 

 

 

% acetic acid

 

 

 

Average % acetic acid

 

 

 

Standard deviation

 

RSD (%)

 

 

Post Lab Questions

1. Answer questions 3, 4 and 5 from the lab manual.

Determination of the Percentage of Acetic Acid in Vinegar

Introduction

Despite the many varieties of vinegar available for purchase, the main components are acetic acid and water. Acetic acid is what gives vinegar its sour taste and distinct (pungent to some) smell. Acetic acid is a simple monoprotic carboxylic acid with the formula CH3COOH also written as C2H402. Store bought vinegar typically ranges from 1-6% acetic acid although it may be higher. Canadian law prohibits the selling of vinegar with an acetic acid concentration greater than 12.3%.

Using the skills developed during the standardization of NaOH experiment, you will determine the percentage of acetic acid in vinegar. Since vinegar is a liquid and not a solid, a measured amount of vinegar will be titrated with a solution of NaOH with known concentration. That is, the NaOH word image 2795 solution with known concentration (molarity) will be used in order to determine the unknown concentration of acetic acid in vinegar.

The reaction of acetic acid with sodium hydroxide will produce sodium acetate (also abbreviated as NaOAc) and water:

word image 2796

After the titration is complete, the amount of acetic acid present in the vinegar sample may be determined. Since the reaction stoichiometry is 1: 1, the number of moles ofNaOH is equivalent to the number of moles of acetic acid. If it takes 29.14 mL of 1.000 M NaOH to titrate 25.00mL of vinegar, the number of moles of acetic acid would be:

1.000 mol NaOH Imol CH3COOH

29.14mL NaOH xx= 0.02914 mol CH3COOH IOOOmL NaOH Imol NaOH

The number of moles of acetic acid can then be converted to mass of acetic acid.

word image 2797

60.05g CH3COOH

0.02914 mol CH3COOH x= 1.750 g CH3COOH

  1. mol CH3COOH

If the density of vinegar is assumed to equivalent to that of water (1 g ml,-l), the percentage of acetic can then be determined:

1.750 g CH3COOH 1mLvinegar x 100% = 6.999% CH3COOH 7%

25.00 mL vinegar lg vinegar

Otherwise, you could measure the mass of vinegar prior to the titration.

Safety Precautions

If either acid or base gets on your skin, flush your skin immediately with large amounts Of water• If at any point you experience a soapy feeling on your skin and you have not been near any soap dispenser’ you can be fairly certain that you have sodium hydroxide on your skin; flush immediately.

This document was prepared by D. Finneran, J. Tierney.

106

Wear eye protection at all times.

All waste solutions may be safely disposed of by flushing down the drain with plenty of water.

Procedure

No data sheet has been provided – you will need to create your own. Give some thought to the information you need to collect PRIOR to performing the experiment.

  1. Remember to clean out the buret as instructed for the standardization ofNaOH experiment.
  2. Since you will be using a volumetric pipette (typically either 25.00 mL or 50.00 mL) for the vinegar, you will need to clean the pipette in a process similar to what you did for the buret. Carefully clean the pipette with the acid as shown in the video. Using the pipette filler, suck a small amount of distilled water into the pipette. Tip and roll the pipette, allowing the water to have contact with the entire inside surface. Dispense the water into the waste beaker. Repeat the rinse with distilled water two more times. After draining the final distilled water rinse, add about 5 mL of the solution to be dispensed (vinegar) from the pipet. Again, roll and tip the pipet so the solution has contact with all the inside surfaces. Dispense the solution into the waste beaker. Repeat this twice more.
  3. Pipet a known amount of vinegar into the Erlenmeyer flask. Remember to touch the end of the pipette to the solution to ensure complete delivery as shown in the video clip. NOTE If so desired, the assumption that the density of vinegar is equivalent to that of water can be avoided by determining the mass of vinegar sample before titrating. If you are planning on determining the mass of the vinegar added, you need to record the mass of the empty Erlenmeyer flask BEFORE adding the vinegar
  4. Add two drops of phenolphthalein solution and stir bar to the vinegar in the Erlenmeyer flask.
  5. word image 2798 Place on stir plate and titrate. Take care not to let the titrant go below the last graduation of the buret. If the pink color has not developed and you are close to the last graduation, record the volume and then add more base to the buret in order to continue with the titration.
  6. Once the pink color lasts for 30 seconds, the titration is complete. Record the final volume.
  7. Determine the volume of titrant actually delivered (final volume — initial volume). Remove the stirbar and discard the contents of the Erlenmeyer flask in the sink. Repeat the titration using a second Erlenmeyer flask and a second aliquot of vinegar. You should have two titration readings that differ by no more than 5%.
  8. Repeat the titration using a third Erlenmeyer flask and a third aliquot of vinegar.
  9. Calculate the average percentage of acetic acid in your vinegar sample as well as the standard deviation and Relative Standard Deviation (RSD) of your results. Report these results to the class via the learning management system (e.g. ANGEL) utilized by your class or as othenvise determined by your instructor.

word image 2799

your

  1. Calculate the class average and compare to your results in

This document was prepared by D. Finneran, J. Tiemey.

107

Determination of [he Percentage of Acetic Acid in Vinegar Post-Lab Questions

Name

  1. Would this procedure work with a sample of apple cider vinegar? Explain why or why not.
  2. Would this procedure work with a sample of balsamic vinegar? Explain why or why not.

word image 2800 3. Write the full and net ionic equations for the reaction of formic acid(aq) with NaOH(aq).

  1. Where does formic acid occur naturally? Why — What purpose does it serve? Remember to cite the reference used.
  2. Write the full and net ionic equations for the reaction of citric acid(aq) NaOH(aq).
  3. Where does citric acid occur naturally? Why — What purpose does it serve? Remember to cite the reference used.
  4. Is the assumption that the density of vinegar is equivalent to that of water valid? Explain.
  5. What was the class average? How do your results compare to the class average? Explain.

This document was prepared by D. Finneran, J. Tiemey.

108

Determination of the Percentage of Acetic Acid in Vinegar

Introduction

Despite the many varieties of vinegar available for purchase, the main components are acetic acid and water. Acetic acid is what gives vinegar its sour taste and distinct (pungent to some) smell. Acetic acid is a simple monoprotic carboxylic acid with the formula CH3COOH also written as C2H402. Store bought vinegar typically ranges from 1-6% acetic acid although it may be higher. Canadian law prohibits the selling of vinegar with an acetic acid concentration greater than 12.3%.

Using the skills developed during the standardization of NaOH experiment, you will determine the percentage of acetic acid in vinegar. Since vinegar is a liquid and not a solid, a measured amount of vinegar will be titrated with a solution of NaOH with known concentration. That is, the NaOH solution with known concentration (molarity) will be used in order to determine the unknown concentration of acetic acid in vinegar.

The reaction of acetic acid with sodium hydroxide will produce sodium acetate (also abbreviated as NaOAc) and water:

word image 2801

After the titration is complete, the amount of acetic acid present in the vinegar sample may be determined. Since the reaction stoichiometry is 1: 1, the number of moles ofNaOH is equivalent to the number of moles of acetic acid. If it takes 29.14 mL of 1.000 M NaOH to titrate 25.00mL of vinegar, the number of moles of acetic acid would be:

1.000 mol NaOH Imol CH3COOH

29.14mL NaOH xx= 0.02914 mol CH3COOH IOOOmL NaOH Imol NaOH

The number of moles of acetic acid can then be converted to mass of acetic acid.

word image 2802

60.05g CH3COOH

0.02914 mol CH3COOH x= 1.750 g CH3COOH

  1. mol CH3COOH

If the density of vinegar is assumed to equivalent to that of water (1 g ml,-l), the percentage of acetic can then be determined:

1.750 g CH3COOH 1mLvinegar x 100% = 6.999% CH3COOH 7%

25.00 mL vinegar lg vinegar

Otherwise, you could measure the mass of vinegar prior to the titration.

Safety Precautions

If either acid or base gets on your skin, flush your skin immediately with large amounts Of water• If at any point you experience a soapy feeling on your skin and you have not been near any soap dispenser’ you can be fairly certain that you have sodium hydroxide on your skin; flush immediately.

This document was prepared by D. Finneran, J. Tierney.

106

Wear eye protection at all times.

All waste solutions may be safely disposed of by flushing down the drain with plenty of water.

Procedure

No data sheet has been provided – you will need to create your own. Give some thought to the information you need to collect PRIOR to performing the experiment.

  1. Remember to clean out the buret as instructed for the standardization ofNaOH experiment.
  2. Since you will be using a volumetric pipette (typically either 25.00 mL or 50.00 mL) for the vinegar, you will need to clean the pipette in a process similar to what you did for the buret. Carefully clean the pipette with the acid as shown in the video. Using the pipette filler, suck a small amount of distilled water into the pipette. Tip and roll the pipette, allowing the water to have contact with the entire inside surface. Dispense the water into the waste beaker. Repeat the rinse with distilled water two more times. After draining the final distilled water rinse, add about 5 mL of the solution to be dispensed (vinegar) from the pipet. Again, roll and tip the pipet so the solution has contact with all the inside surfaces. Dispense the solution into the waste beaker. Repeat this twice more.
  3. Pipet a known amount of vinegar into the Erlenmeyer flask. Remember to touch the end of the pipette to the solution to ensure complete delivery as shown in the video clip. NOTE If so desired, the assumption that the density of vinegar is equivalent to that of water can be avoided by determining the mass of vinegar sample before titrating. If you are planning on determining the mass of the vinegar added, you need to record the mass of the empty Erlenmeyer flask BEFORE adding the vinegar
  4. Add two drops of phenolphthalein solution and stir bar to the vinegar in the Erlenmeyer flask.
  5. word image 2803 Place on stir plate and titrate. Take care not to let the titrant go below the last graduation of the buret. If the pink color has not developed and you are close to the last graduation, record the volume and then add more base to the buret in order to continue with the titration.
  6. Once the pink color lasts for 30 seconds, the titration is complete. Record the final volume.
  7. Determine the volume of titrant actually delivered (final volume — initial volume). Remove the stirbar and discard the contents of the Erlenmeyer flask in the sink. Repeat the titration using a second Erlenmeyer flask and a second aliquot of vinegar. You should have two titration readings that differ by no more than 5%.
  8. Repeat the titration using a third Erlenmeyer flask and a third aliquot of vinegar.
  9. Calculate the average percentage of acetic acid in your vinegar sample as well as the standard deviation and Relative Standard Deviation (RSD) of your results. Report these results to the class via the learning management system (e.g. ANGEL) utilized by your class or as othenvise determined by your instructor.

word image 2804

your

  1. Calculate the class average and compare to your results in

This document was prepared by D. Finneran, J. Tiemey.

107

Determination of [he Percentage of Acetic Acid in Vinegar Post-Lab Questions

Name

  1. Would this procedure work with a sample of apple cider vinegar? Explain why or why not.
  2. Would this procedure work with a sample of balsamic vinegar? Explain why or why not.

word image 2805 3. Write the full and net ionic equations for the reaction of formic acid(aq) with NaOH(aq).

  1. Where does formic acid occur naturally? Why — What purpose does it serve? Remember to cite the reference used.
  2. Write the full and net ionic equations for the reaction of citric acid(aq) NaOH(aq).
  3. Where does citric acid occur naturally? Why — What purpose does it serve? Remember to cite the reference used.
  4. Is the assumption that the density of vinegar is equivalent to that of water valid? Explain.
  5. What was the class average? How do your results compare to the class average? Explain.

This document was prepared by D. Finneran, J. Tiemey.

108

Experiment – Determination of the Percentage of Acetic Acid in Vinegar

Directions: To complete the experiment, read the laboratory experiment in the manual, watch the video below, and complete the data table below.

The experimental report must be submitted to the appropriate Blackboard assignment folder.

Reading Assignment: Determination of the Percentage of Acetic Acid in Vinegar

 

Experimental Videos: Determination of the Percentage of Acetic Acid in Vinegar

 

https://youtu.be/YqfvRBJ-iPg

https://youtu.be/9pS7Q4MQCYI

https://youtu.be/d1XTOsnNlgg

 

 

 

Simulated Data:

Complete the data table. Remember Significant figures

The molar mass of acetic acid is 60.05g/mol.

Assume that the density of vinegar is equal to that of water (1g/mL)

 

Trial 1

Trial 2

Trial 3

Molarity of NaOH (M)

0.700

0.700

0.700

Volume of vinegar used (mL)

25.0

25.0

25.0

Initial buret reading (mL)

15.65

0.00

0.00

Final buret reading (mL)

46.70

31.70

32.30

Volume of NaOH used (mL)

 

 

 

Volume of NaOH used (L)

 

 

 

Moles of NaOH used (mol)

 

 

 

Moles of acetic acid in sample (mol)

 

 

 

Mass of solution (g)

 

 

 

Mass of acetic acid (g)

 

 

 

% acetic acid

 

 

 

Average % acetic acid

 

 

 

Standard deviation

 

RSD (%)

 

 

Post Lab Questions

1. Answer questions 3, 4 and 5 from the lab manual.

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