Write Group 2 metal reactions with dilute acids
Predict and balance reactions of the Group 2 metals with dilute hydrochloric and sulfuric acids.
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Group trends are qualitative unless data are supplied. Show physical states and balance equations; distinguish reaction from dissolution and precipitation. This sequence does not replace supervised practical experience. Written practice is self-checked
Before you begin
- Use Group 2 formulas, ionic charges, state symbols, balanced equations and acid reaction patterns.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What chloride formula is formed when M²⁺ combines with chloride ions?
What you will learn
- Predict the salt and hydrogen from a metal–acid reaction
- Balance equations for both specified acids
- Recognise when an insoluble sulfate can affect the observation
Hydrochloric acid forms a chloride and hydrogen
A Group 2 metal reacts with dilute hydrochloric acid: M(s) + 2HCl(aq) → MCl₂(aq) + H₂(g). The salt formula follows from M²⁺ and Cl⁻. For example, Mg + 2HCl → MgCl₂ + H₂.
A more reactive Group 2 metal generally reacts more vigorously under comparable conditions. The metal is oxidised to M²⁺ while hydrogen ions are reduced to hydrogen gas; at this level, use the observable pattern and balanced molecular equation.
Sulfuric acid gives a sulfate; solubility can change the reaction surface
The general equation with dilute sulfuric acid is M(s) + H₂SO₄(aq) → MSO₄ + H₂(g). Many sulfates dissolve, but BaSO₄ is insoluble and CaSO₄ is sparingly soluble.
A solid sulfate layer can coat a metal surface and slow further acid contact, especially for barium. Do not infer that all Group 2 metals give an equally rapid, uninterrupted reaction with sulfuric acid. The word dilute matters; concentrated sulfuric acid can behave differently and is outside this equation model.
Pause and explain
What gas forms when a Group 2 metal reacts with dilute hydrochloric acid?
Worked example
Write balanced equations for magnesium with dilute hydrochloric acid and barium with dilute sulfuric acid.
Show the worked solution
- Mg²⁺ requires two chloride ions, so MgCl₂ forms.
- Two HCl molecules provide two H atoms for H₂.
- Ba²⁺ and SO₄²⁻ combine 1:1 to give BaSO₄; balance the hydrogen as H₂.
Answer Mg + 2HCl → MgCl₂ + H₂; Ba + H₂SO₄ → BaSO₄(s) + H₂.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write and balance the reaction of calcium with dilute hydrochloric acid.
Give me a hint
Form CaCl₂ and H₂, then count chlorine and hydrogen atoms.
Compare my reasoning
- Ca²⁺ needs two Cl⁻, giving CaCl₂.
- Two HCl provide two Cl and two H atoms.
- Ca + 2HCl → CaCl₂ + H₂.
Ca(s) + 2HCl(aq) → CaCl₂(aq) + H₂(g).
Look for these in your work
- Correct chloride formula
- Equation balanced
- Hydrogen state shown
Write the equation for strontium reacting with dilute sulfuric acid.
Give me a hint
The sulfate and Sr²⁺ combine in a 1:1 formula unit.
Compare my reasoning
- The salt is SrSO₄.
- One H₂SO₄ supplies one sulfate and two hydrogen ions.
- The two hydrogen atoms form H₂.
Sr(s) + H₂SO₄(aq) → SrSO₄(s) + H₂(g).
Look for these in your work
- Sulfate formula correct
- Equation balanced
- Products identified
A learner says barium should fizz continuously in dilute sulfuric acid because it is very reactive. Correct the prediction.
Give me a hint
Consider both the hydrogen-producing reaction and the sulfate's solubility.
Compare my reasoning
- The initial reaction can form BaSO₄ and H₂.
- BaSO₄ is insoluble and can coat the barium surface.
- That layer can restrict acid contact, so continuous vigorous fizzing is not guaranteed.
Ba + H₂SO₄ → BaSO₄(s) + H₂; insoluble BaSO₄ can coat the metal and slow or stop further visible reaction.
Look for these in your work
- Equation represented
- Precipitate solubility stated
- Observation qualified
Common mistakes
- Writing MCl instead of MCl₂
- Forgetting that hydrogen is diatomic H₂
- Writing M₂SO₄ for a divalent metal
- Ignoring an insoluble sulfate layer in an observation
What can you explain now?
What chloride formula is formed when M²⁺ combines with chloride ions?
Compare with the explanation
MCl₂
Two Cl⁻ ions balance one M²⁺ ion.
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Make it stick
What formula pattern and gas identify metal reactions with dilute HCl and H₂SO₄, and what sulfate exception affects observations?
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