Determination of the Amounts of Sodium Hydroxide Solution and Sodium Carbonate in a Mixed Solution

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Experiment 2

Determination of the Amounts of Sodium Hydroxide Solution and Sodium Carbonate in a Mixed Solution

Date of Experiment: 21/9/2005

Objective: To determine the percentage by mass of Sodium Hydroxide and Sodium Carbonate in a mixed solution.

Introduction

Sodium carbonate and sodium hydroxide are both alkaline in nature. When hydrochloric acid is added to the mixture, sodium hydroxide reacts like this:

NaOH + HCl -----> NaCl + H2O ....................... (1)

Sodium carbonate reacts with hydrochloric acid in a similar way but the reaction comes in 2 steps:

Na2CO3 + HCl ----------->NaHCO3 + NaCl............. (2)

NaHCO3 + HCl ----------->NaCl + H2O + CO2.......... (3)

The pH conditions in which reactions (1) and (2) take place are approximately the same: they both occur at a relatively higher pH (at a pH value higher than 7). Reaction (3) is quite different from the other 2 reactions. It takes place at a lower pH (at a pH value lower than 7).

So, using the 2 acid-base indicators, the end points for the reactions can be found. Phenolphthalein turns from pink to colorless as the