Preparing Soluble Salts
Chemistry: Cambridge International GCSE Supplement, topic 7.3.2
Preparing Soluble Salts
Soluble salts are prepared by reacting acids with alkalis, metals, bases, or carbonates. Steps involve reaction, filtration, evaporation for crystals, and drying.
Introduction to soluble salts preparation
- Soluble salts dissolve well in water.
- Chemists prepare soluble salts by reacting acids with other substances.
- The four main methods: titration with alkali, excess metal, excess insoluble base, and excess insoluble carbonate.
- Each method requires separation and purification steps.
Preparation by titration with alkali
- Use an acid and an alkali to make soluble salts by titration.
- Slowly add alkali to acid until neutralisation occurs (pH 7).
- Record the exact volumes when neutral.
- Repeat without indicator, then evaporate water to crystallise salt.
- Separate crystals by filtration and dry them.
Preparation using excess metal, base or carbonate
- React acid with excess metal (like zinc), base (like copper oxide), or carbonate (like calcium carbonate).
- The acid reacts until all the acid is used up.
- Filter to remove leftover solids.
- Evaporate the filtrate to crystallise pure soluble salt.
Separation and purification of salts
- After reaction, solutions must be filtered to remove solids.
- Evaporate the solution gently to form crystals.
- Crystals form as the solution concentrates.
- Dry crystals with filter paper to purify.
- This process yields pure soluble salts for experiments.
Hydrated and anhydrous substances
- Hydrated substances contain water molecules chemically joined.
- Anhydrous substances have no water.
- Example: Copper sulfate turns blue when hydrated, white when anhydrous.
- Water of crystallisation affects the appearance and properties.
Test yourself on Preparing Soluble Salts
What is a key characteristic of soluble salts?