Percentage of Acetic Acid in Vinegar

Background:

Most commercial vinegars are made by fermentation, but some, such as the white vinegar, are obtained by the dilution of 100% acetic acid. The usual mass percentage of acetic acid in vinegar is between 4.0% and 5.5% regardless of how it is produced. The quantity of acetic acid in a sample of vinegar may be found by titrating the sample against a standard basic solution. In this experiment, you will titrate with burets to determine what volume of potassium hydroxide solution of known molarity is needed to neutralize a measured quantity of vinegar. From your results and the molarity of potassium hydroxide, KOH, you can calculate the molarity of the vinegar.

Purpose:

Determine the end point of an acid-base titration.

Calculate the molarity of vinegar, using experimental data.

Calculate the percentage of acetic acid in vinegar.

Procedure:

1.  Make a data table in your lab book that includes trial #, and initial and final readings in mL for 1M NaOH. (see below)

2.  Rinse your buret with a small amount of the NaOH solution, discard after rinsing. Fill the buret to the zero mark, and record initial reading.

3.  Measure 20 mL of vinegar and pour into a 125mL Erlenmeyer flask. Add two drops of phenolphthalein.

4.  Titrate the vinegar with the NaOH solution until a faint pink color persists, and record final volume for the buret.

5.  Rinse the contents of the flask down the drain, rinse with water, and repeat the titration once more.

6.  Clean up as directed by the teacher.

Data Table:

Trial # / Initial Volume Reading NaOH / Final Volume Reading NaOH / Volume NaOH (mL) / Volume Vinegar (mL)
1
2

Calculations:

1.  Calculate the volumes of vinegar and NaOH used for each of the trials.

2.  Use the titration formula to determine the molarity of vinegar in each of the trials. The balanced equation is on the board.

3.  Calculate the average molarity of the vinegar.

4.  Use the average molarity for vinegar to determine the mass of acetic acid in 1 L of vinegar.

5.  Calculate the percentage of acetic acid in your vinegar sample. The density of vinegar is 1.00 g/mL. Assume the mass of 1 L of vinegar is 1000 g. (Hint: The mass of acetic acid in 1 L of vinegar, calculated in item 4, divided by the total mass of vinegar in a liter and multiplied by 100 gives the percentage of acetic acid in vinegar.)

6.  Look on the vinegar bottle to get the actual % acetic acid and calculate your last percent error.

Percentage of Acetic Acid in Vinegar

Background:

Most commercial vinegars are made by fermentation, but some, such as the white vinegar, are obtained by the dilution of 100% acetic acid. The usual mass percentage of acetic acid in vinegar is between 4.0% and 5.5% regardless of how it is produced. The quantity of acetic acid in a sample of vinegar may be found by titrating the sample against a standard basic solution. In this experiment, you will titrate with burets to determine what volume of potassium hydroxide solution of known molarity is needed to neutralize a measured quantity of vinegar. From your results and the molarity of potassium hydroxide, KOH, you can calculate the molarity of the vinegar.

Purpose:

Determine the end point of an acid-base titration.

Calculate the molarity of vinegar, using experimental data.

Calculate the percentage of acetic acid in vinegar.

Procedure:

1.  Make a data table in your lab book that includes trial #, and initial and final readings in mL for 1M KOH. (see below)

2.  Rinse your buret with a small amount of the KOH solution, discard after rinsing. Fill the buret to the zero mark, and record initial reading.

3.  Measure 20 mL of vinegar and pour into a 125mL Erlenmeyer flask. Add two drops of phenolphthalein.

4.  Titrate the vinegar with the KOH solution until a faint pink color persists, and record final volume for the buret.

5.  Rinse the contents of the flask down the drain, rinse with water, and repeat the titration once more.

6.  Clean up as directed by the teacher.

Data Table:

Trial # / Initial Volume Reading KOH / Final Volume Reading KOH / Volume KOH (mL) / Volume Vinegar (mL)
1
2

Calculations:

1.  Calculate the volumes of vinegar and KOH used for each of the trials.

2.  Use the titration formula to determine the molarity of vinegar in each of the trials. The balanced equation is on the board.

3.  Calculate the average molarity of the vinegar.

4.  Use the average molarity for vinegar to determine the mass of acetic acid in 1 L of vinegar.

5.  Calculate the percentage of acetic acid in your vinegar sample. The density of vinegar is 1.00 g/mL. Assume the mass of 1 L of vinegar is 1000 g. (Hint: The mass of acetic acid in 1 L of vinegar, calculated in item 4, divided by the total mass of vinegar in a liter and multiplied by 100 gives the percentage of acetic acid in vinegar.)

6.  Look on the vinegar bottle to get the actual % acetic acid and calculate your last percent error.