⚛️

Salts

Preparation, Solubility & Crystallisation

Tap → or swipe to begin

Learning Objectives

Prepare salts from acids and bases

Use solubility rules to predict salt formation

Understand crystallisation

Identify insoluble salts

Write ionic equations for salt formation

Apply practical salt preparation methods

What is a Salt?

Salt: Ionic compound formed from the reaction of an acid and a base.

General formula: Cation from base + Anion from acid
Examples: NaCl, CuSO₄, Ca(NO₃)₂, AgCl

Salt Formation Methods

Method 1: Acid + Alkali (neutralisation) → Soluble salt
Method 2: Acid + Metal → Salt + Hydrogen (for reactive metals)
Method 3: Acid + Carbonate → Salt + CO₂ + Water

Solubility Rules

SOLUBLE SALTS (dissolve in water):

• ALL Group 1 (alkali metal) salts are soluble
• ALL chlorides soluble (except AgCl, PbCl₂)
• ALL nitrates soluble
• ALL sulfates soluble (except BaSO₄, PbSO₄)
INSOLUBLE SALTS: Carbonates, hydroxides (except Group 1 & Ca), phosphates

Preparing Soluble Salts

Add acid to metal/carbonate/alkali

Filter to remove unreacted material

Evaporate solution to obtain crystals

Cool crystals to dry them

Measure mass and purity

Preparing Insoluble Salts

Mix two soluble salts in solution

Double displacement reaction occurs

Insoluble salt precipitates out

Filter to collect solid

Wash and dry precipitate

Ionic Equations for Precipitation

Write the ionic equation by showing only reacting particles:

Full: AgNO₃ + NaCl → AgCl + NaNO₃
Ionic: Ag⁺ + Cl⁻ → AgCl↓
Spectator ions (Na⁺, NO₃⁻) are omitted

Crystallisation

Crystallisation: Process of forming pure crystals from solution.

Heat solution to dissolve salt
Evaporate some water
Cool solution (solubility decreases)
Crystals form as solution becomes supersaturated
Filter and dry crystals

Why Crystals Form

When solution cools, solubility decreases:

• Hot water dissolves more salt
• Cool water dissolves less salt
• Excess solute must come out of solution
• Forms solid crystals (pure salt)
• Slow cooling = larger, purer crystals

Salt Properties

All salts are ionic compounds

All are solids at room temperature

All have high melting and boiling points

Soluble salts conduct electricity when dissolved/molten

Insoluble salts do not conduct