PROTOCOL N° 3

DETERMINATION OF THE TOTAL ALKALINITY
OF A WATER SAMPLE

REAGENTS

• Aqueous solution of hydrochloric acid, 0.1 mol/dm³ HCl
• Solution of methyl orange acid-base indicator.

PROCEDURE

1. Place 10 mL of the water sample inside an Erlenmeyer,
2. Add 2 drops of the indicator solution,
3. Drop by drop, counting the number of drops, keep adding hydrochloric acid solution and stir carefully, until the colour turns to a light pink,
4. Record the results.

DATA TREATMENT

Values of total alkalinity are given by the following equation:

Total Alkalinity / mg/L CaCO₃ = n x 25

where n is the number of drops of added hydrochloric acid solution.