IGCSE · Practice questions · Group VII: the halogens

Who displaces whom?

Six original Cambridge-style questions on the halogens: physical properties, trends and displacement reactions.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

More reactive displaces less reactive.

Cl₂ green gas, Br₂ red-brown liquid, I₂ grey-black solid.
Down the group: darker, denser, less reactive.
Displacement: only a more reactive halogen reacts.
Colours: bromine orange, iodine brown in solution.

Recall

[3 marks]

Give the colour and state at room temperature of chlorine, bromine and iodine.

Chlorine: pale yellow-green gas. ✓
Bromine: red-brown liquid. ✓
Iodine: grey-black solid. ✓

Analysis

[3 marks]

Chlorine water is added to potassium bromide solution. Describe what is seen, name the products and write the balanced equation.

The solution turns orange (from colourless). ✓
Products: potassium chloride and bromine. ✓
Cl₂ + 2KBr → 2KCl + Br₂ ✓

Explain

[2 marks]

Explain why iodine does not react with potassium chloride solution.

Iodine is less reactive than chlorine. ✓
A halogen can only displace a less reactive halogen from its compounds. ✓

Analysis

[3 marks]

Predict three properties of astatine, the element below iodine in Group VII.

It is a (black) solid at room temperature. ✓
It is denser than iodine. ✓
It is less reactive than iodine (it cannot displace iodine from iodides). ✓

Recall

[2 marks]

(Extended) Write the ionic equation for the reaction between bromine and potassium iodide solution, and state which species is reduced.

Br₂ + 2I⁻ → 2Br⁻ + I₂ ✓
Bromine is reduced (it gains electrons). ✓

Analysis

[2 marks]

A student has three unlabelled solutions: potassium chloride, potassium bromide and potassium iodide. Describe how chlorine water could be used to identify them.

Add chlorine water to each: no change with potassium chloride. ✓
Orange with potassium bromide (bromine formed); brown with potassium iodide (iodine formed). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.