Preparation of Soluble Salts Using Titration (SQA National 5 Chemistry): Revision Note

Producing soluble salts by titration

What is a salt?

• A salt is a compound that is formed during a neutralisation reaction

  • This is when the hydrogen atom in an acid is replaced by a metal

• For example, if we replace the H in HCl with a potassium atom, then the salt potassium chloride is formed, KCl

Using titrations

• Titrations can be used to prepare a soluble salt

  • For example, sodium chloride from an acid and alkali

• The acid and alkali are reacted together in a neutralisation reaction

• When the acid and alkali are completely neutralised only a salt and water will be present in the solution

hydrochloric acid + sodium hydroxide → sodium chloride + water

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

Steps to prepare a soluble salt

 Method:

1. Use a pipette to measure a fixed volume of alkali into a conical flask and add a few drops of an indicator 

   • For example, phenolphthalein

2. Add the acid into the burette and note the starting volume

3. Add the acid very slowly from the burette to the conical flask until the indicator changes to the appropriate colour

4. Note and record the final volume of acid in the burette and calculate the volume of acid added (final volume of acid - initial volume of acid)

5. Repeat the experiment using the exact same volumes, but without the indicator, to produce a pure, uncontaminated salt solution

Making salt crystals

1. Once the salt solutions are formed solid salts can be formed by crystallisation

2. The salt solution is gently heated to evaporate some of the water

3. This forms a saturated solution

   • To check the solution is saturated dip a cold, glass rod into the solution and see if crystals form on the end

4. The saturated solution is then left in a warm, dry place to allow the rest of the water to evaporate slowly, forming pure crystals

Making salt crystals from a salt solution