Experiment - Preparation of Sodium Chloride

Introduction

The only method of preparing a water soluble salt from a water soluble base (also called an alkali) is to use titration. This is where a known volume of base is reacted with an acid using an indicator. The indicator shows when the correct volume of acid has been added (i.e. when the reaction is fully complete) by changing colour.

Diagram

Method

[ A ] Using a 25 cm3 measuring cylinder, measure out 25 cm3 of the hydrochloric solution provided. Use a dropping pipette to make sure that you measure out the acid as accurately as possible.

[ B ] Place the 25 cm3 of hydrochloric acid solution into a 250 cm3 conical flask. Add a few drops of an indicator (for example phenolphthalein, which turns from colourless in acidic solution to pink in alkaline solution) and note the indicator's name as well as the initial colour of the indicator in the acid.

[ C ] Carefully fill a burette with the sodium hydroxide solution provided to above the zero mark, and run out the excess into a beaker, ensuring the space under the tap is full of alkali. Then run the alkali from the burette into the conical flask slowly, making sure to swirl the concical flask during the addition, until the indicator changes colour i.e. all the acid has reacted. Note the change in colour of the indicator. Note down the volume of alkali used to neutralize the 25 cm3 of hydrochloric acid. Repeat this procedure a further two times, or until you have two results that agree closely with one-another (within 0.5 cm3 of each other).

Now repeat the procedure once more, but omit the indicator from the conical flask containing the hydrochloric acid. Add the correct volume of sodium hydroxide from the burette. This will give a clear colourless solution containing only sodium chloride dissolved in water. Evaporate some of the liquid using a Bunsen burner, tripod, gauze and a evaporating bowl, and leave to crystallize for a few days.

Questions

(i) Write up all your observations and results as they occur.

(ii) Write a full balanced chemical equation for this reaction and the reaction of sodium hydroxide with

(a) sulphuric acid,

(b) nitric acid.