Experiment 10 - Acid-Base Titrimetry

Objectives

1. To standardize an acid, HCl, solution.
2. To determine the concentration of an unknown Na₂CO₃, sodium carbonate solution.

Introduction

Alkaline conditions are found in many natural waters and may arise in boiler water due to the accumulation of calcium carbonate and other minerals derived from the water supply.

Since the alkalinity is due to a mixture of substances, no single neutralization reaction can be written. The sample is simply titrated to pH 4.6, and the result calculated as if all of the alkalinity is due to calcium carbonate.

This experiment involves the titration of sodium carbonate, Na₂CO₃, by a strong acid, HCl. 

Na₂CO₃ (aq) + 2 HCl (aq) 2 NaCl (aq) + CO₂ (g) + H₂O (l)

Note that each mole of carbonate requires two moles of acid for complete titration.  Titration to the bromocresol green end-point ensures that all of the carbonate are converted to CO₂ and H₂O.