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InkFlaskCambridge IGCSE

Pupil sheet · Formulae and equations

Balancing equations — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. construct

Hydrogen burns in chlorine to make hydrogen chloride. Balance the equation by typing the numbers in front.

Write a number in front of each formula. Leave it blank for 1.

____ H2(g) + ____ Cl2(g) → ____ HCl(g)

Nudge (only if you are stuck): Count chlorine atoms on each side. How many HCl molecules hold two chlorine atoms?

2. explain

A pupil "balances" H2 + O2 → H2O by writing H2 + O2 → H2O2. Why is this wrong?

Circle one answer.

  • Subscripts may be changed on the left, but not on the right
  • Oxygen atoms are not allowed on the right of an equation
  • The atoms in H2 + O2 → H2O2 still don't balance
  • H2O2 is a different substance; only the numbers in front of the formulae may change

Nudge (only if you are stuck): What is H2O2? Is it the product of the reaction?

3. construct

Zinc granules (small lumps of zinc) react with dilute sulfuric acid, fizzing, and leave a solution of zinc sulfate. Fill in the state symbols: Zn(__) + H2SO4(__) → ZnSO4(__) + H2(__).

Zn(__)

H2SO4(__)

ZnSO4(__)

H2(__)

Nudge (only if you are stuck): Which substance is a solid, which are dissolved in water, and what makes the fizzing?

4. construct

Hot iron reacts with chlorine gas to make iron(III) chloride. Balance the equation.

Write a number in front of each formula. Leave it blank for 1.

____ Fe(s) + ____ Cl2(g) → ____ FeCl3(s)

Nudge (only if you are stuck): Chlorine is 2 on the left and 3 on the right. What is the smallest number both 2 and 3 go into?

5. construct

Sodium reacts with water, giving sodium hydroxide solution and hydrogen gas. Balance the equation.

Write a number in front of each formula. Leave it blank for 1.

____ Na(s) + ____ H2O(l) → ____ NaOH(aq) + ____ H2(g)

Nudge (only if you are stuck): Hydrogen comes as H2. Try 2 in front of H2O and see what else must change.

6. construct

Calcium hydroxide solution is neutralised by hydrochloric acid. Balance the equation.

Write a number in front of each formula. Leave it blank for 1.

____ Ca(OH)2(aq) + ____ HCl(aq) → ____ CaCl2(aq) + ____ H2O(l)

Nudge (only if you are stuck): Ca(OH)2 has two O and two H. How many HCl molecules does it need for the chlorine in CaCl2?

7. construct

Black copper(II) oxide powder, CuO, dissolves in warm dilute sulfuric acid, giving a blue solution of copper(II) sulfate and water. (a) Write the word equation. (b) Write the balanced symbol equation with state symbols.

(a) Word equation

(b) Symbol equation with state symbols

Nudge (only if you are stuck): The formula of copper(II) oxide is given. Which other formulae do you know from part 1? Then check the clues for each state.

8. construct

Supplement. Barium chloride solution is mixed with sodium sulfate solution, and a white precipitate of barium sulfate forms: BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq). Which is the ionic equation?

Circle one answer.

  • Ba2+(aq) + SO42−(aq) → BaSO4(s)
  • Na+(aq) + Cl−(aq) → NaCl(aq)
  • BaCl2(aq) + SO42−(aq) → BaSO4(s) + 2Cl−(aq)
  • Ba2+(aq) + SO42−(aq) → BaSO4(aq)

Nudge (only if you are stuck): Which ions are the same before and after? Leave them out.

9. construct

Supplement. When sodium hydroxide solution is added to copper(II) sulfate solution, a blue precipitate of copper(II) hydroxide forms. Balance the ionic equation.

Write a number in front of each formula. Leave it blank for 1.

____ Cu2+(aq) + ____ OH−(aq) → ____ Cu(OH)2(s)

Nudge (only if you are stuck): Cu(OH)2 holds two hydroxide ions. Then check the charges.

10. deduce

Supplement. "Solid calcium carbonate is heated strongly. It breaks down into solid calcium oxide and carbon dioxide gas." Which equation does this information describe?

Circle one answer.

  • CaCO3(s) → CaO(s) + CO2(g)
  • CaCO3(aq) → CaO(aq) + CO2(g)
  • CaCO3(s) → CaO(s) + CO2(l)
  • CaCO3(s) → Ca(s) + CO3(g)

Nudge (only if you are stuck): Pick out each substance and its state from the words, then check the formulae.

11. deduce

Supplement. Iron(III) oxide, Fe2O3, is a solid. When hydrogen gas is passed over hot iron(III) oxide, it forms iron and steam. Balance the equation, then check that each state symbol shown matches the information.

Write a number in front of each formula. Leave it blank for 1.

____ Fe2O3(s) + ____ H2(g) → ____ Fe(s) + ____ H2O(g)

Nudge (only if you are stuck): Fe2O3 has three oxygen atoms. Each one ends up in a molecule of water.

12. construct / deduce

Water from an old iron pipe looks slightly orange. A technician tests it: the water contains dissolved iron(III) chloride, FeCl3. When sodium hydroxide solution is added, a red-brown precipitate of iron(III) hydroxide, Fe(OH)3, forms, and sodium chloride stays dissolved. (a) Write the word equation. (b) Write the balanced symbol equation with state symbols. (c) Supplement: write the ionic equation.

(a) Word equation

(b) Symbol equation with state symbols

(c) Supplement: ionic equation

Nudge (only if you are stuck): In (b), how many hydroxide ions does Fe(OH)3 hold? In (c), which ions stay dissolved on both sides?