What this practice covers
These questions are drawn from past CIE 0654 Co-ordinated Sciences papers and filtered to stoichiometry. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on stoichiometry, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Leaving out the brackets in Cu(OH)₂ or Mg(NO₃)₂.
- Writing the negative ion first in an ionic formula.
- Balancing an equation by changing a formula, for instance writing O instead of O₂ or H₂O₂ instead of H₂O.
- Counting only one element and declaring an equation balanced.
- Writing every ion on both sides of an "ionic" equation instead of cancelling the spectators.
- Giving a precipitate the state symbol (aq).
- Forgetting to multiply the contents of brackets when calculating an Mr.
- Giving relative atomic mass a unit.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Stoichiometry revision notes.