Preparation of Crystals of Soluble Salts

Preparation of Crystals of Soluble Salts

General Method

• To make a soluble salt, you first need to produce a solution which contains the required anion and cation.
• This is usually done by a reaction between an acid and an insoluble substance, such as a base or carbonate.

Acid and Base Reaction

• The acid and the base (or carbonate) react to produce a salt and water.
• The base should be added to the acid until no more reacts, and then any excess solid is removed by filtration.

Crystallization

• The water can then be removed from the solution to leave the salt.
• This is usually done by evaporation to produce a saturated solution, and then allowing the solution to cool so that the salt will crystallise out.
• The crystals of salt can then be separated from the solution by filtration and dried.

Specific Reactions

• Different acids will react with different bases to produce different salts.
• The name of the salt produced depends on the metal in the base and the type of acid used.
• For example, sulfuric acid and copper oxide react to produce copper sulphate, and hydrochloric acid and magnesium oxide react to produce magnesium chloride.

Safety Precautions

• When handling acids and bases, safety eyewear should be worn to protect the eyes.
• Additionally, care should be taken to avoid skin contact with these substances.
• During the evaporation step, the solution should be heated gently to avoid spattering.

Experimental Errors

• In the crystallisation step, not all the salt may crystallise out, so the yield may be less than expected.
• Solubility of the salt can also affect the yield.
• In the filtration step, care should be taken to avoid loss of solid.