Understanding Inorganic chemistry: Extraction and uses of metals to Chemical tests: Edexcel IGCSE Chemistry Explained

From pulling metals out of the ground to identifying unknown ions in a test tube, these four topics connect industrial chemistry to the practical detective work of qualitative analysis.

The second half of the Edexcel IGCSE Chemistry inorganic section covers extraction and uses of metals, acids and alkalis, salt preparation, and chemical tests. Across Europe and internationally, these topics form the practical core of any chemistry course, and the edexcel exam tests them consistently. Whether you are sitting the exam in London, Dubai or Lagos, the chemistry is the same, and the mark scheme expects the same precision.

These edexcel igcse chemistry revision notes for inorganic chemistry: extraction and uses of metals to chemical tests cover every specification point, with worked examples and the kind of detail the igcse 4ch1 mark scheme rewards.

Extraction and uses of metals

Most metals are found in the Earth's crust as ores, which are rocks containing enough of the metal compound to make extraction worthwhile. Very unreactive metals, such as gold, are sometimes found as the uncombined element because they do not react with other substances easily.

The method of extraction depends on the metal's position in the reactivity series:

Carbon can only reduce metal oxides of metals that are less reactive than carbon itself. For metals above carbon in the reactivity series, the energy cost of electrolysis is the only option, which is why aluminium is more expensive to produce than iron despite being more abundant in the crust.

Uses of metals are linked to their properties:

• Aluminium: low density, resistant to corrosion (protective oxide layer), good conductor. Used for aircraft bodies, drink cans, overhead power cables.
• Copper: excellent electrical conductor, malleable, does not react with water. Used for electrical wiring, plumbing pipes.
• Iron and steel: Iron is strong but rusts. Steel is an alloy of iron. Low-carbon (mild) steel is easily shaped (car bodies), high-carbon steel is hard (cutting tools), stainless steel (with chromium and nickel) resists corrosion (cutlery, surgical instruments).

An alloy is a mixture of a metal with one or more other elements, usually other metals or carbon. Alloys are harder than pure metals because the atoms of different sizes disrupt the regular arrangement of layers, preventing them from sliding over each other as easily.

Acids, alkalis and titrations

Acids and alkalis are central to inorganic chemistry. The pH scale runs from 0 to 14:

Indicators help classify solutions. Litmus turns red in acid and blue in alkali. Phenolphthalein is colourless in acid and pink in alkali. Methyl orange is red in acid and yellow in alkali. Universal indicator gives a range of colours corresponding to pH values.

In aqueous solution, acids are a source of H⁺ ions and alkalis are a source of OH^- ions. Neutralisation is the reaction between an acid and an alkali:

H⁺(aq) + OH^-(aq) → H₂O(l)

Titration is the technique used to find the exact volume of acid needed to neutralise a known volume of alkali (or vice versa). The key steps: use a pipette to measure a fixed volume of alkali into a conical flask, add indicator, then add acid from a burette until the indicator changes colour (the end point). Record the volume of acid used. Repeat until concordant results (within 0.10 cm³) are obtained.

Acids, bases and salt preparations

A base is a substance that neutralises an acid. A base that dissolves in water is called an alkali. Bases include metal oxides, metal hydroxides and ammonia.

The edexcel specification defines acids and bases in terms of proton transfer: an acid is a proton (H⁺) donor, and a base is a proton acceptor.

Reactions of acids:

• Acid + metal → salt + hydrogen (e.g. Mg + 2HCl → MgCl₂ + H₂)
• Acid + base (metal oxide) → salt + water (e.g. CuO + H₂SO₄ → CuSO₄ + H₂O)
• Acid + metal hydroxide → salt + water
• Acid + metal carbonate → salt + water + carbon dioxide (e.g. CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂)

The name of the salt depends on the acid used: hydrochloric acid produces chlorides, sulfuric acid produces sulfates, nitric acid produces nitrates.

Preparing salts:

Method 1: Soluble salt from an insoluble reactant. Add excess insoluble base (e.g. copper(II) oxide) to warm acid. The excess ensures all acid is used up. Filter off the excess solid. Evaporate the filtrate gently, then leave to crystallise.

Method 2: Soluble salt from an acid and alkali. Titration method. Find the exact volumes needed using an indicator, then repeat without the indicator to produce a pure solution. Evaporate and crystallise.

Method 3: Insoluble salt by precipitation. Mix two soluble solutions that contain the ions needed. The insoluble salt forms as a precipitate. Filter, wash with distilled water, and dry.

Chemical tests

The specification requires you to identify specific gases, cations and anions. This is where chemistry becomes forensic: given an unknown substance, which tests do you run?

Gas tests:

Flame tests for cations:

Cation tests with sodium hydroxide solution:

• NH₄⁺: warm with NaOH, ammonia gas produced (turns damp red litmus blue).
• Cu²⁺: blue precipitate of Cu(OH)₂.
• Fe²⁺: green precipitate of Fe(OH)₂.
• Fe³⁺: brown precipitate of Fe(OH)₃.

Anion tests:

• Cl^-, Br^-, I^-: add dilute nitric acid then silver nitrate solution. Cl^- gives a white precipitate (AgCl), Br^- gives a cream precipitate (AgBr), I^- gives a yellow precipitate (AgI).
• SO₄^2-: add dilute hydrochloric acid then barium chloride solution. A white precipitate of BaSO₄ confirms sulfate.
• CO₃^2-: add dilute hydrochloric acid. Effervescence (fizzing), and the gas turns limewater milky (carbon dioxide).

Testing for water: Anhydrous copper(II) sulfate is white. If water is present, it turns blue (hydrated copper(II) sulfate forms). To test whether a water sample is pure, check its boiling point: pure water boils at exactly 100 degrees C at standard pressure.

Common mistakes

• Mixing up flame test colours. Lithium is red, not orange-red. Calcium is orange-red, not red. Potassium is lilac, not purple.
• Forgetting to acidify before adding silver nitrate or barium chloride. The acid removes interfering ions (e.g. carbonate or sulfite) that would give false positives.
• Confusing the method for soluble vs insoluble salt preparation. You do not filter when making a salt by titration (there is no excess solid). You filter when using an insoluble base in excess.
• Saying "carbon is used to extract aluminium." Aluminium is above carbon in the reactivity series, so carbon cannot reduce it. Electrolysis is required.

Connecting these topics in the exam

The edexcel igcse chemistry inorganic chemistry: extraction and uses of metals to chemical tests material is deeply practical. Exam questions in this area often present you with a scenario: an unknown powder, a set of test tubes, and instructions to identify the substance. You need to recall the correct test, describe the observation, and state the conclusion. This sequence of test-observe-conclude is the backbone of the igcse 4ch1 inorganic chemistry: extraction and uses of metals to chemical tests specification.

The edexcel igcse chemistry explained in this section also rewards candidates who understand the logic behind each test, not just the memorised procedure. Why does silver nitrate need to be acidified with nitric acid? Because without the acid, carbonate or hydroxide ions might produce a precipitate of their own, giving a false positive for a halide. Understanding the why makes the facts stick and helps you answer "suggest" questions where the exam presents a slightly modified procedure.

Self-check questions

1. Explain why aluminium must be extracted by electrolysis rather than by reduction with carbon.
2. Describe how you would prepare a pure, dry sample of lead(II) sulfate starting from lead(II) nitrate solution and sodium sulfate solution.
3. An unknown solution gives a green precipitate when sodium hydroxide solution is added. Identify the cation present.
4. A student adds acidified silver nitrate to a solution and observes a cream precipitate. Which halide ion is present?
5. Write a balanced equation for the reaction between zinc and dilute sulfuric acid, including state symbols.

The inorganic chemistry: extraction and uses of metals to chemical tests edexcel igcse section demands both factual recall and the ability to apply those facts to unfamiliar contexts. These edexcel igcse chemistry notes cover the specification points, but the real test is whether you can use them under timed conditions. For more edexcel igcse chemistry practice questions on this material, explore the Green Bridge CBT platform, where everything is aligned to the igcse 4ch1 specification.