O-LevelChemistryBonding & Structure5070/22 · Oct/Nov 2015 · Q710 Marks

The structures of diamond and silicon dioxide are shown. silicon atom oxygen atom diamond silicon dioxide

(a)Describe one similarity in the structures of diamond and silicon dioxide.[1]
(b)Explain why silicon dioxide has a high melting point.[2]
(c)Silicon dioxide reacts with hot concentrated sodium hydroxide to form sodium silicate, Na2SiO3. Deduce the formula of the silicate ion.[1]
(d)Explain why diamond does not conduct electricity.[1]
(e)Graphite is a form of carbon which conducts electricity. Graphite is used as electrodes in electrolysis. What is the meaning of the term electrolysis?[1]
(f)(i)Aluminium is extracted by the electrolysis of molten aluminium oxide dissolved in cryolite. Construct the equation for the reaction at the anode (positive electrode),[1]
(f)(ii)the cathode (negative electrode).[1]
(g)An isotope of silicon is represented by the symbol 29 14Si. Deduce the number of protons and neutrons in this isotope. number of protons number of neutrons[1]
(h)Silicon has a relative atomic mass of 28. Define the term relative atomic mass.[1]

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Mark scheme

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

[1] (a) (atoms) arranged tetrahedrally/tetrahedral (structure)/(bent) hexagonal (structure)/four atoms round carbon and four atoms round silicon/both giant (structures)/both lattices/both macromolecules/each has one atoms surrounded by four others (1)
[2] (b) giant structure/lattice (1) (all) bonds are strong/takes a lot of energy to break bonds/needs high temperature to break the bonds (1)
[1] (c) SiO3²- (1)
[1] (d) no mobile electrons/does not have delocalised electrons/does not have free electrons/all electrons are used in bonding (1)
[1] (e) breakdown/decomposition of substance using electric current (1)
[1] (f) (i) 2O²- → O2 + 4e¯ (1)
[1] (f) (ii) Al³+ + 3e¯ → Al (1)
[1] (g) protons 14 and neutrons 15 (1)
[1] (h) (weighted) mass of atom on scale where carbon-12 atom weighs 12 units/idea of mass of an atom comparison with C-12 atom (1)

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