O-LevelChemistryMetals & Reactivity5070/21 · May/June 2015 · Q710 Marks

Molybdenum is a transition element. It is used to make steel that is extremely hard. Molybdenum can be manufactured by heating together molybdenum(VI) oxide, MoO3, and aluminium.

(a)Construct the equation for this reaction.[1]
(b)Explain why this reaction involves both oxidation and reduction.[1]
(c)What mass of molybdenum can be made from 125g of molybdenum(VI) oxide? [Ar: Mo, 96] mass of molybdenum =[3]
(d)Which metal is the less reactive, aluminium or molybdenum? Explain your answer.[1]
(e)(i)Molybdenum has a melting point of 2623 °C. Describe metallic bonding, with the aid of a labelled diagram.[2]
(e)(ii)Suggest why molybdenum has a much higher melting point than aluminium.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.

[1] (a) MoO3 + 2Al → Al2O3 + Mo (1)
[1] (b) Reduction since MoO3 loses oxygen AND Oxidation since Al gains oxygen (1)
[1] (c) Mr of MoO3 = 144 (1) Moles of MoO3 is 0.868 (1) Mass of Mo = 83.3 (g) (1)
[1] (d) Molybdenum because aluminium can displace it (1)
[1] (e) (i) Closely packed metal ions (1) Delocalised electrons/free electrons/sea of electrons (1)
[1] (e) (ii) ANY TWO FROM (Much) strong(er) attraction between electrons and positive ions (1) Needs more energy to break the attraction/needs more heat to overcome the attraction (1) Greater charge on cation (1) More delocalised electrons (1)

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