O-LevelChemistryAtomic Structure5070/22 · May/June 2019 · Q214 Marks
The table shows some of the properties of the elements in Group III of the Periodic Table. element | proton (atomic) number | atomic radius /nm | melting point /°C --- | --- | --- | --- B | 5 | 0.080 | 2306 Al | 13 | 0.125 | 660 Ga | 31 | 0.125 | 30 In | 49 | 0.150 | 157 Τι | 81 | 0.155 | 304 Nh | 113 | |
- (a)(i)Nihonium, Nh, has only recently been discovered. It has not been possible to measure its atomic radius and melting point because it is too radioactive. (i) Estimate the atomic radius of Nh. .............................................................................................................................. nm[1]
- (a)(ii)Explain, using data from the table, why it is difficult to estimate the melting point of nihonium.[1]
- (b)Boron has a giant covalent structure. Explain why boron has a high melting point.[1]
- (c)(i)Aluminium is produced by the electrolysis of molten aluminium oxide. Aluminium oxide contains Al3+ and O2- ions. (i) Describe the composition of the electrolyte used in this electrolysis.[1]
- (c)(ii)Name the material used for the electrodes in this electrolysis.[1]
- (c)(iii)Construct equations for the reactions taking place at the: negative electrode ............................................................................................................................ positive electrode. ...............................................................................................................................[2]
- (d)Aluminium reacts with aqueous copper(II) chloride in a redox reaction. 2Al(s) + 3Cu2+(aq) → 2Al3+(aq) + 3Cu(s) Which particle is oxidised? Explain your answer.[1]
- (e)Explain why a piece of aluminium in water does not react.[2]
- (f)Aluminium chloride is a soluble salt. Describe how a pure sample of aluminium chloride crystals can be made from aluminium.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.
- [1] 2(a)(i) 0.155 -0.190 (nm)
- [1] 2(a)(ii) the melting point goes up and down
- [1] 2(b) has many strong bonds (that have to be broken or overcome) / needs lots of energy to break or overcome many bonds
- [1] 2(c)(i) aluminium oxide (dissolved) in (molten) cryolite
- [1] 2(c)(ii) carbon/graphite
- [2] 2(c)(iii) negative electrode: Al 3+ + 3e → Al(1) positive electrode: 2O2- → O2 + 4e¯ (1)
- [1] 2(d) Al because it loses electrons
- [2] 2(e) has a layer of oxide / aluminium oxide layer (1) layer is impermeable (to water) / coating is impermeable (to water) (1)
- [4] 2(f) use hydrochloric acid (1) use excess aluminium (1) filter (off aluminium) (1) leave filtrate in warm place / evaporate solution to point of crystallisation then leave / leave in the sun (1)
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