The acidity of vinegar

Procedure

• Weight 10 g of vinegar inside the erlenmeyer flask.
• Add 25 mL of water and some drops of phenolphthalein.
• Titrate the solution with the sodium hydroxide solution and record the volume used.

Theoretical explanation

The acidity level is the weight percentage of acetic acid in vinegar. The reaction that takes place during the titration is as follows:

CH₃COOH + NaOH CH₃COONa + H₂O

The pK_a of acetic acid is 4.76. Once we have added just enough base to deprotonate all the acid, the next drop of NaOH causes the pH of the solution being titrated to abruptly rise from 5-6 to over 10. This pH change causes phenolphthalein to turn pink, as its endpoint pH is around 8-8.5. At this point, the titration is considered finished.

The equation would be:

V_NaOH · C_NaOH = n_NaOH = nÀ_{c. acètic}

The molecular weight of acetic acid is 60 g/mol. Acidity levels are expressed in g_{acetic acid}/g_vinegar in percentage.