2: To use a standardised solution of hydrochloric acid to standardise a solution of sodium hydroxide, and hence prepare a sample of sodium chloride salt

Theory

• A solution of sodium hydroxide of unknown concentration can be made up and its exact concentration can be determined by titrating against a previously standardised solution of hydrochloric acid (HCl)

• The salt sodium chloride (NaCl) can then be prepared by evaporation

Equation

HCl + NaOH → NaCl + H2O

Procedure

1) Filling the burette with the standard solution of hydrochloric acid solution

2) Making the sodium hydroxide up into a solution so it can be standardised

3) Transferring an exact volume of sodium hydroxide solution into a conical flask

4) Carrying out the titration

Suitable indictor for this titration

Methyl orange

Justification for the indicator

• It is a strong acid-strong base titration, the end point occurs between a pH of 3 and 11

• Methyl orange changes colour between pH 3 and 5 coinciding with this end point

Colour change observed at end point:

Yellow → pink

(Base) → (Acid)

Why is it required to find the exact concentration of sodium hydroxide by titration/why can a standard solution of sodium hydroxide not be made up directly

Sodium hydroxide is not a primary standard and cannot be made into a standard solution directly - it absorbs water vapour from the air (deliquescent) so its precise mass cannot be weighed accurately – it cannot be obtained in a pure state

How was it possible to have a standard solution of hydrochloric acid to use in this titration despite the fact it is not a primary standard?

The hydrochloric acid was previously standardised by titrating it against a standard solution of anhydrous sodium carbonate