Salt Formula Jigsaw
Match cations and anions to form neutral salts
What this lesson covers
Why it matters
Acids are like puzzle pieces with a loose hydrogen tab. Pull that tab out and slot in a metal ion to build a stable salt.
Predict first
Why do we need two chloride ions for every one calcium ion to make calcium chloride?
Salts are electrically neutral. The total positive charge from metal ions must equal the total negative charge from acid radicals.
- Calcium is twice as heavy as chlorine
- To balance the +2 charge of Ca with two -1 charges of Cl — correct
- Because calcium is a metal and chlorine is a gas
- To make the formula look symmetrical
What you do
Drag the metal ions and acid radicals together. Swap H⁺ for metals. Balance the charges to form neutral salts.
Check yourself
What is the formula for the salt formed when magnesium reacts with hydrochloric acid?
Magnesium has a valency of +2 (Mg²⁺) and chloride has -1 (Cl⁻). Two Cl⁻ ions are needed to balance one Mg²⁺ ion.
Why is the formula for aluminium sulphate Al₂(SO₄)₃?
Al³⁺ needs two ions to reach +6 charge. SO₄²⁻ needs three ions to reach -6 charge. The net charge is zero.
If both replaceable H⁺ ions in H₂SO₄ are completely replaced by Na⁺, what normal salt is formed?
H₂SO₄ releases two H⁺ ions. To maintain neutrality, two Na⁺ ions are required for every one SO₄²⁻ ion.
- MgCl
- MgCl₂ — correct
- Mg₂Cl
- MgHCl
- Aluminium has 3 protons
- Two Al³⁺ ions (+6 total) balance three SO₄²⁻ ions (-6 total) — correct
- Sulphate is heavier than aluminium
- It is the standard notation for all sulphates
- NaSO₄
- Na₂SO₄ — correct
- Na(SO₄)₂
- NaHSO₄