1.2 Word and balanced symbol equations
6 exam questions worth 9 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Balance this equation:
__Mg + O2 → __MgO
Mark scheme
2Mg + O2 → 2MgO
Model answer
2Mg + O2 → 2MgO
Balance this equation:
__Na + __H2O → __NaOH + H2
Mark scheme
2Na + 2H2O → 2NaOH + H2
Model answer
2Na + 2H2O → 2NaOH + H2
Explain why chemical equations must be balanced.
Mark scheme
- atoms are not created or destroyed (in a reaction) (1)
- so mass is conserved / same number of each atom on each side (1)
Model answer
Atoms cannot be created or destroyed in a reaction, so there must be the same number of atoms of each element on both sides.
What do the state symbols (s), (l), (g) and (aq) mean?
Mark scheme
all four correct (2); two or three correct (1)
- solid, liquid, gas, aqueous / dissolved in water
Model answer
(s) solid, (l) liquid, (g) gas and (aq) aqueous, meaning dissolved in water.
Write a word equation for the reaction of zinc with hydrochloric acid to make zinc chloride and hydrogen.
Mark scheme
zinc + hydrochloric acid → zinc chloride + hydrogen
Model answer
zinc + hydrochloric acid → zinc chloride + hydrogen
A student balances H2 + O2 → H2O by writing H2 + O2 → H2O2.
Explain why this is wrong, and give the correct balanced equation.
Mark scheme
- changing the subscript makes a different substance / hydrogen peroxide (1)
- 2H2 + O2 → 2H2O (1)
Model answer
Changing the small number makes a different substance (hydrogen peroxide). The correct equation is 2H2 + O2 → 2H2O.
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