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3.3.2Atomic Structure and the Periodic Table

Acids and Carbonates

5 min read 5 parts Lesson 1 of 10 Unit quiz

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Section 1 of 5The Reaction Pattern

3.3.2 Acids and Carbonates

Acids react with metal carbonates in a predictable pattern that produces a salt, water and carbon dioxide.

Products
  • An acid reacts with a metal carbonate to form a salt, water and carbon dioxide gas.
Effervescence
  • Bubbles of carbon dioxide are seen, which distinguishes carbonate reactions from reactions with metal oxides or hydroxides.
Naming the salt
  • The metal in the salt comes from the carbonate, and the acid determines the rest of the salt name.
Testing the gas
  • Bubbling the gas through limewater makes the limewater turn milky, which confirms carbon dioxide.

Section 2 of 5Worked Word and Symbol Equations

Each equation below follows the same pattern, so the method can be reused for other acids and carbonates.

1
Hydrochloric acid reacts with sodium carbonate to give sodium chloride, water and carbon dioxide: 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂.
2
Sulfuric acid reacts with calcium carbonate to give calcium sulfate, water and carbon dioxide: H₂SO₄ + CaCO₃ → CaSO₄ + H₂O + CO₂.
3
Check each equation by counting the atoms of every element on both sides, which must be equal.
4
Include state symbols where they are asked for, such as (s) for solids and (g) for carbon dioxide.

Section 3 of 5Salts Formed From Acids

Salts Formed From Acids
Hydrochloric acid
  • Forms chloride salts, such as sodium chloride from sodium carbonate.
Sulfuric acid
  • Forms sulfate salts, such as calcium sulfate from calcium carbonate.
Nitric acid
  • Forms nitrate salts, such as copper(II) nitrate from copper(II) carbonate.
Balancing
  • Use the formula of the acid to decide how many hydrogen atoms and anions the salt needs.

Section 4 of 5Worked Example

Question Write the balanced symbol equation for hydrochloric acid reacting with sodium carbonate.

  1. Write the formulae
    • HCl and Na₂CO₃ on the left;
      • NaCl, H₂O and CO₂ on the right.
  2. Balance sodiumNa₂CO₃ provides two sodium atoms, so two NaCl are needed, which requires two HCl.
  3. Check hydrogen
    • two H on the left (2HCl) and two H in H₂O on the right;
      • chlorine: two on each side.

Answer 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂

Section 5 of 5Exam Checklist & Tips

3.3.2 – Key Points for the Exam

  • Salt An ionic compound formed when the hydrogen ions of an acid are replaced by a metal or ammonium ion.
  • Effervescence Fizzing caused by a gas being released during a reaction.
  • Carbonate A compound containing the CO₃²⁻ ion.
  • Neutralisation A reaction between an acid and a base that produces a salt and water.

Common Mistakes

  • Forgetting to include water among the products of an acid and carbonate reaction.
  • Writing the formula of sulfuric acid incorrectly, for example as H₂SO₃.
  • Using a splint to test the gas; carbon dioxide is tested with limewater.
  • Confusing carbonate reactions with reactions of metal oxides, which produce no gas and therefore no effervescence.
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