Quick answer: A chemical equation shows reactants turning into products. This grade 8 science test on balancing equations has 8 questions worth 20 marks, to do in 45 minutes: reactants and products, balance three equations and ozone. The mark scheme is on a separate page; free printable PDF.
This test covers reactants and products, balancing, conservation of atoms and conservation of mass. Show all your working, and write the final balanced equations clearly. You have 45 minutes and the test is worth 20 marks.
Level: Grade 8 science (Year 9 · Class 8) · Curriculum: MS-PS1-2, MS-PS1-5
Question 1 Reactants and products (2 marks)
In the reaction H₂ + Cl₂ → 2 HCl, name the reactants and the product and state the total number of atoms of each element on the left.Question 2 Balance three equations (3 marks)
Balance each equation.- K + O₂ → K₂O (1 mark)
- Mg + N₂ → Mg₃N₂ (1 mark)
- H₂ + Br₂ → HBr (1 mark)
Question 3 Ozone (3 marks)
Ozone changes to oxygen as shown: O₃ → O₂.- Count the oxygen atoms on each side. (1 mark)
- Explain why the equation is not balanced. (1 mark)
- Write the balanced equation. (1 mark)
Question 4 Zinc sulfide (3 marks)
Zinc reacts with sulfur: Zn + S → ZnS. 13.0 g of zinc reacts with 6.4 g of sulfur.- Calculate the mass of zinc sulfide formed. (1 mark)
- State the law you used. (1 mark)
- Calculate the mass of zinc sulfide formed from 26.0 g of zinc and enough sulfur, using the ratio. (1 mark)
Question 5 Conservation of atoms (3 marks)
Use the reaction H₂ + Cl₂ → 2 HCl to explain why atoms are conserved in a chemical reaction.Question 6 Spot the error (2 marks)
A student balances Mg + O₂ → MgO as Mg + O₂ → MgO₂. Explain the mistake and write the correct equation.Question 7 State symbols (2 marks)
Zn(s) + 2 HCl(aq) → ZnCl₂(aq) + H₂(g). State what (s), (aq) and (g) mean and identify the gas.Question 8 Evidence of a reaction (2 marks)
Give four observations that suggest a chemical reaction has happened.
