You perform an acid base titration to standardize a phosphoric acid solution by placing 50 ml of sulfuric acid in a flask with a couple drops of phenolphthalein

Only one of the hydrogen atoms of the acetic acid molecule is acidic:

Equation 1. HC2H3O2 (aq)



H

+

(aq) + C2H3O2

–

(aq)

acetic acid hydrogen ion acetate ion

The structural formula for acetic acid is shown to the right.

The hydrogen attached to the oxygen atom is acidic while the other hydrogen

atoms are not.

Another way of representing the acidity of acetic acid is to show its reaction with water:

Equation 2. HC2H3O2(aq) + H2O(l)



H3O

+

(aq) + C2H3O2

–

(aq)

acetic acid hydronium ion acetate ion

Here the acetic acid protonates (transfers a proton to) the water molecule. In fact, the hydrogen ion (H+

)

is very reactive and doesn't exist in water. However, there is evidence that the hydronium ion does exist.

Sometimes equation 1 is used because of its simplicity.

To determine the amount of acetic acid in vinegar (typically 4-5% by mass) we will use an acid-base

titration (neutralization reaction). In this experiment we titrate acetic acid with sodium hydroxide (a

strong base). The reaction of acetic acid with sodium hydroxide is shown below:

Equation 3. HC2H3O2 (aq) + NaOH (aq)



NaC2H3O2(aq) + H2O (l)

acetic acid sodium hydroxide sodium acetate

Explanation: