AQA GCSE FOUNDATION Chemistry: Making Salts

AQA GCSE Foundation Chemistry: Making Salts

This tutorial will cover the methods for preparing and purifying salts in AQA GCSE Foundation Chemistry.

1. Methods for Preparing Salts

There are two main methods for preparing salts:

• Reaction of an acid with a metal: This method is suitable for preparing salts of active metals like magnesium, zinc, and iron.

  • Procedure:

    1. Add the metal to the acid in a beaker.
    2. Observe the reaction: bubbles of hydrogen gas will be released.
    3. Heat the mixture gently to speed up the reaction.
    4. Once the reaction is complete, carefully evaporate the solution to dryness to obtain the salt.

• Reaction of an acid with a base (alkali or carbonate): This method is suitable for preparing a wide range of salts.

  • Procedure:

    1. Add the base to the acid in a beaker, stirring constantly.
    2. Observe the reaction: the solution will often heat up and bubbles of carbon dioxide may be released.
    3. Continue adding the base until the acid is neutralized.
    4. Carefully evaporate the solution to dryness to obtain the salt.

2. Methods for Purifying Salts

• Filtration: This method is used to separate insoluble impurities from a salt solution.

  • Procedure:

    1. Set up a filter funnel with filter paper.
    2. Pour the salt solution through the filter paper, collecting the filtrate (the liquid that passes through) in a beaker.
    3. The insoluble impurities will be trapped on the filter paper.

• Recrystallization: This method is used to purify a salt by taking advantage of its solubility.

  • Procedure:

    1. Dissolve the impure salt in a minimum amount of hot water.
    2. Allow the solution to cool slowly. As the solution cools, the salt will crystallize out, leaving impurities in solution.
    3. Separate the crystals from the solution by filtration.
    4. Dry the crystals thoroughly.

• Evaporation: This method is used to obtain a solid salt from a solution.

  • Procedure:

    1. Heat the salt solution gently in an evaporating basin.
    2. As the water evaporates, the salt will become more concentrated.
    3. When most of the water has evaporated, the salt will start to crystallize.
    4. Stop heating when the salt crystals are dry.

3. Safety Precautions

• Wear safety goggles to protect your eyes from splashes.
• Always add acid to water, never water to acid. This will prevent a violent reaction.
• Work in a well-ventilated area to avoid inhaling harmful fumes.
• Handle hot glassware with caution.
• Dispose of chemicals properly.

4. Examples of Salts

Here are some examples of salts that can be prepared using these methods:

• Sodium chloride (NaCl): prepared by reacting hydrochloric acid with sodium hydroxide.
• Copper sulfate (CuSO4): prepared by reacting sulfuric acid with copper oxide.
• Magnesium chloride (MgCl2): prepared by reacting hydrochloric acid with magnesium.

Note: This tutorial provides a basic overview of preparing and purifying salts. Always refer to your textbook and lab manual for specific instructions and safety procedures.