Inorganic Chemistry Problem Solving

This final lesson brings together everything you have learned about inorganic chemistry and focuses on the types of problem-solving questions that appear in Edexcel A-Level exams. You will practise identifying unknown salts, predicting products, working through ligand substitution reactions, calculating oxidation states, and interpreting data.

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Identifying Unknown Salts

Exam questions frequently describe a series of tests performed on an unknown compound and ask you to identify it. The approach is systematic:

1. Flame test — identifies the metal cation (Li⁺, Na⁺, K⁺, Ca²⁺, Ba²⁺, Cu²⁺)
2. NaOH test — identifies transition metal cations by precipitate colour
3. Anion tests — identifies the anion (CO₃²⁻ with acid + limewater, SO₄²⁻ with BaCl₂, halides with AgNO₃)

Worked Example

A white solid gives the following results:

• Flame test: pale green
• Dissolves in water to give a colourless solution
• Adding dilute HNO₃ then AgNO₃ gives a white precipitate that dissolves in dilute NH₃

Analysis:

• Pale green flame → Ba²⁺
• White precipitate with AgNO₃ that dissolves in dilute NH₃ → Cl⁻
• The compound is barium chloride (BaCl₂)

Strategy Tips