How to Measure Titratable Acidity of Vinegar

Objective

To measure titratable acidity of vinegar  

Background

Some foods contain acids that gives them a sour taste. Sourness can play a big role in the overall flavor and acceptability of food. But, apart from their sensory effect, acids can help to improve texture in jams and jellies, and reduce bacteria and other microbial growth in a variety of foods. In this lab you will determine the titratable acidity in acetic acid (vinegar). Titratable acidity determines how much of a base (NaOH) is required to neutralize an acid. The base, also known as the titrant, is of known concentration. A color indicator will be used to determine the end point of the acid-base reaction. The indicator is phenolphthalein. Phenolphthalein is colorless in acid and turns pink in neutral and basic solutions. Therefore, when the sample turns pink, it means that all of the acid has been neutralized. You can then apply the following formula to calculate the total acidity.  

Where,

 N = normality of titrant (NaOH) (in this lab, it is 1.0)

V1 = volume of titrant (ml)

V2 = Volume of sample (ml)

Eq wt. = Equivalent weight of predominant acid in the sample (60.05 for acetic acid)

Materials

1. Vinegar
2. 1 N sodium hydroxide
3. Phenolphthalein indicator
4. Measuring cylinder
5. 50 ml Burette
6. Burette stand with clamp
7. Two 250 ml beakers

Method

1. Place a 250 ml beaker at the base of your burette
2. Fill a second 250 ml beaker with about 200 ml of NaOH
3. Place a funnel on top of your burette and rinse the burette with about 10 ml of NaOH
4. Fill the burette with NaOH to the 0 ml mark (at this point, the total volume in the burette will be 50 ml)
5. Drain the tip to remove any air pocket at the base and add more NaOH to get the volume back to the zero mark
6. Use a measuring cylinder to measure 5 ml of vinegar and pour it into a 250 ml Erlenmeyer flask
7. Add approximately 3-4 drops of phenolphthalein indicator to the Erlenmeyer flask
8. Titrate by adding NaOH to the vinegar gradually with continuous mixing until the solution changes to a persistent light pink
9. Record the amount of titrant that was needed to neutralize the acid
10. Calculate titratable acidity
11. Repeat the titration twice
12. Average the two values that are the closest (show your calculations)