CAIE A Level Chemistry 9701 · Atoms, molecules and stoichiometry
Green hydrated chromium(III) sulfate has the formula . When heated, it loses water of crystallisation to form the anhydrous salt.
Describe: (a) the meaning of the terms hydrated, anhydrous and water of crystallisation. (b) the formula of anhydrous chromium(III) sulfate. (c) a balanced chemical equation for the dehydration reaction, including state symbols. (d) why the empirical and molecular formulae of anhydrous chromium(III) sulfate are the same.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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