Vinegar Analysis

A low percentage acid solution are seen in many commercial product. Vinegar are solution of water with 4 to 5 % acetic acid CH3COOH by weight. Often many product we buy in the market has one or two sweet smelling (flavor) and colour, this smelling and colour is added in other to make the product see better. Chief constituent of commonly use flavorings and preserving food substance is vinegar. The acidity of vinegar add tang and has bacteriostatic ability, as is use to inhibit the growth of bacteria.

In the analysis, we going to determine the strength of the vinegar by titration. And the neutralization of acetic acid with standardized sodium hydroxide solution as shown in the equation bellow;

            HC3H3O2(aq) + NaOH(aq)     →  NaC2H3O2(aq) + H2O(L)

In this practical, any vinegar sample can used, but I will recommend colourless vinegar because of less interference it give during indicator end point observation colour change.

When the concentration of the vinegar is higher than the concentration of the standard sodium hydroxide solution, then the original vinegar solution should be diluted ten times before the commencement of the titrations. On the final note, the dilution factor must be taken into account when calculating the original vinegar concentration of the solution.

Practical procedure

Step 1

Clean and dry the following material

1. 500ml plastic bottle
2. 100ml beaker

Step 2

Clean and rinse the following glassware with distilled water

1. 25ml volumetric flask
2. 250ml volumetric flask
3. 250ml Erlrnmeyer flask
4. 50ml Buret.

Step 3

1. Measure accurately 25.00ml of vinegar into a clean volumetric flask of 250ml.
2. Dilute the vinegar with deionized water to 250ml mark on the volumetric flask.
3. Stopper the flask and mix the solution well by inverting it slowly for at least 10 minute to completely mix the content.
4. Now transfer the diluted vinegar solution to a clean dry 500ml plastic bottle, label the content and the container with your name.

Step 4

1. Wash the volumetric flask with loot of tap water and rinse it severally with deionized water and left it air dry at room temperature.

Step 5

1. Measure 50ml of diluted vinegar solution into 100ml beaker
2. Rinse 25ml volumetric pipet, many times with a portion of diluted vinegar solution from the beakers.
3. Be careful to add water to the diluted vinegar solution in the beaker accidentally.

Step 6

1. Pipet carefully 25ml of the diluted vinegar solution into 250ml Erlenmeyer flask
2. To the Erlenmeyer flaks, add 50ml of deionized water
3. Now add 2 drop of phenolphthalein indicator to the solution and then swirl the flask for the mixture to be mix thoroughly.

Step 7

1. Rinse 50ml burets many times with a few milliliter of standardized sodium hydroxide solution.
2. Fill the burets with the standard sodium hydroxide solution
3. Make sure no bubble on the tip of the burets

Step 8

1. Record the volume or the burets to the nearest 0.01ml
2. Now titrate the acid sample, stop the titration when a faint pink appear. That is the end point
3. Now record the final volume of the burets to the nearest 0.01ml
4. Repeat the titration for two or more trial.
5. However the number of trial run depend on the availability standardized sodium hydroxide solution
6. And your data precision.

Here are the calculation involved the practical

Moles of base = (Molarity of base) x (liters of base)

Moles of acid (diluted vinegar) = Moles of base

                                                      Moles of acid (diluted vinegar)

Molarity of diluted vinegar = —————————————-

                                                     Liter of acid (diluted vinegar)

Note that molarity of the original vinegar can be known if the times ten dilution of 25ml to 250ml solution of the vinegar is kept in mind, for obtaining diluted vinegar, that the molarity has already been determine by standard NaOH titration solution.,

Gram of HC2H3O2     molHC2H3O2  gHC2H3O2        L vinegar         mL vinegar

——————— =   ——————- x ————- x        ————       x —————–

Gram of vinegar      L of vinegar         molHC2H3O3   mL vinegar    g vinegar

Density of vinegar = 1.0052g/ml

% weight of HC2H3O2          Grams of HC2H3O2

—————————-  =      ————————–    x 100

Weight of vinegar                  Grams of vinegar