O-LevelChemistryStoichiometry5070/22 · Oct/Nov 2016 · Q510 Marks

Nickel carbonyl, Ni(CO)4, reacts with hydrogen iodide. Ni(CO)4(l) + 2HI(g) → NiI2(s) + H2(g) + 4CO(g)

(a)Calculate the percentage by mass of nickel in nickel carbonyl. %[2]
(b)Calculate the maximum volume of gas formed at room temperature and pressure when 1.71 g of nickel carbonyl reacts completely with hydrogen iodide. maximum volume of gas formed[3]
(c)The structure of a nickel carbonyl molecule is shown. CO OC — Ni — CO CO Predict two physical properties of nickel carbonyl.[2]
(d)The proton numbers and accurate relative atomic masses of cobalt and nickel are shown in the table. proton number | cobalt 27 | nickel 28 relative atomic mass | 58.9 | 58.7 Suggest why cobalt has a higher relative atomic mass than nickel.[2]
(e)An aqueous solution of hydrogen iodide is a strong acid. What is meant by the term strong acid?[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2016). The mark or mark type is shown in brackets.

[2] 34.5%
[1] If two marks not scored, 171 (for molar mass of nickel carbonyl) scores 1 mark
[1] mol nickel carbonyl = 1.71/171 OR 0.01 (mol)
[1] mol gases = (0.01) × 5/idea of multiplying mol × 5
[1] volume of gases = 1.2 dm³/1200 cm³ (units must be correct)
[1] low melting point/low boiling point
[1] does not conduct electricity
[1] cobalt has greater proportion of heavier isotopes than nickel/nickel has lower proportion of lighter isotopes than nickel
[1] acid that is completely ionised/acid that is completely dissociated/acid that releases all ionisable hydrogen

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