CAIE A Level Chemistry 9701 · Atoms, molecules and stoichiometry
A student is told that a white solid is a pure ionic compound containing only aluminium ions and oxide ions. Explain how the formula of this compound can be deduced from the charges on the ions. In your answer, state the charge on each type of ion and explain how these charges determine the ratio of ions in the formula.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.