Acid reactions: choose the salt and the other products
Use the reacting substance and acid identity to predict products without assuming every acid reaction makes hydrogen.
Section C7.1 · The characteristic properties of acids and bases
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Balance equations and read state symbols.
- Distinguish a metal, oxide, hydroxide and carbonate.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which formula represents a carbonate?
What you will learn
- Describe reactions of suitable metals, bases and carbonates with acids.
- Name the salt from the acid and the reacting metal or ammonium component.
Choose the pattern from the reactant
A suitable reactive metal with a dilute acid can produce a salt and hydrogen: Mg+2HCl→MgCl₂+H₂. A basic metal oxide or hydroxide with an acid produces a salt and water: CuO+2HCl→CuCl₂+H₂O. A carbonate with an acid produces a salt, water and carbon dioxide: CaCO₃+2HCl→CaCl₂+H₂O+CO₂. The three patterns have different gas predictions, so identify the reacting class first.
Do not extend the metal pattern to every metal or every acid condition. Copper does not produce hydrogen from dilute hydrochloric acid in this comparison. Nitric acid and other oxidising-acid conditions can behave differently from the stated dilute non-oxidising acid pattern. These are interpretation examples for supervised chemistry, not a home experiment recipe.
The acid supplies the salt family
Hydrochloric acid makes chloride salts, sulfuric acid sulfate salts and nitric acid nitrate salts in the appropriate neutralisation patterns. Magnesium with dilute sulfuric acid gives magnesium sulfate, while copper(II) oxide with nitric acid gives copper(II) nitrate. The metal or positive-ion identity comes from the other reactant; the acid name alone does not determine the whole salt.
Balance only after writing correct formulas. For copper(II) oxide and nitric acid, CuO+2HNO₃→Cu(NO₃)₂+H₂O keeps the nitrate group together. Changing a subscript to balance atoms would change the substance. An insoluble coating or an unsuitable metal can complicate a preparation, so a correct general equation does not establish that any material is a sensible practical choice.
Sources for this lesson
Pause and explain
Which gas belongs to the stated dilute-acid reaction with a carbonate?
Worked example
Predict and balance the products of magnesium carbonate with hydrochloric acid, naming the gas.
Show the worked solution
- A carbonate with an acid gives salt, water and carbon dioxide.
- The positive component is magnesium and hydrochloric acid supplies chloride: MgCl₂.
- Balance MgCO₃+2HCl→MgCl₂+H₂O+CO₂; the gas is carbon dioxide, not hydrogen.
Answer MgCO₃+2HCl→MgCl₂+H₂O+CO₂; carbon dioxide forms.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Predict and balance zinc with dilute hydrochloric acid in the suitable-metal pattern.
Give me a hint
Choose chloride and hydrogen, then conserve chlorine and hydrogen atoms.
Compare my reasoning
- Zinc forms zinc chloride, ZnCl₂.
- The other product is hydrogen, H₂.
- Balance Zn+2HCl→ZnCl₂+H₂.
Zn+2HCl→ZnCl₂+H₂.
Look for these in your work
- The salt formula is correct.
- Atoms and the gas prediction agree.
Predict and balance sodium carbonate with sulfuric acid.
Give me a hint
Carbonate adds carbon dioxide to the salt-and-water pattern.
Compare my reasoning
- The salt is sodium sulfate, Na₂SO₄.
- Water and CO₂ are the other products.
- Na₂CO₃+H₂SO₄→Na₂SO₄+H₂O+CO₂ is balanced.
Na₂CO₃+H₂SO₄→Na₂SO₄+H₂O+CO₂.
Look for these in your work
- Acid identity selects sulfate.
- All three products and their atoms are accounted for.
A report predicts hydrogen for both CuO+HCl and Mg+HCl. Correct the products and explain the distinction.
Give me a hint
Copper oxide is a base; magnesium is a suitable reactive metal.
Compare my reasoning
- CuO+2HCl→CuCl₂+H₂O follows acid–base neutralisation.
- Mg+2HCl→MgCl₂+H₂ follows the suitable-metal pattern.
- Reactant class determines the other product; the shared acid does not make both reactions release hydrogen.
CuO makes copper(II) chloride and water; Mg makes magnesium chloride and hydrogen.
Look for these in your work
- Both equations use the correct reacting class.
- The reason for the different product is explicit.
Common mistakes
- Predicting hydrogen from an acid–carbonate reaction.
- Naming sulfate when the acid is hydrochloric acid.
- Changing formula subscripts to balance an equation.
- Assuming every metal reacts with dilute hydrochloric acid.
What can you explain now?
Name the salt and other product from copper(II) oxide reacting with sulfuric acid.
Compare with the explanation
Copper(II) sulfate and water.
A basic oxide neutralises an acid; sulfuric acid provides the sulfate part of the salt.
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Make it stick
Write one balanced equation for each acid pattern. Cover the products and recover them from reactant class and acid identity.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.