EJC 2023 8873 'A' Level H1 Chemistry Suggested Solutions P2

EUNOIA JUNIOR COLLEGE

1312 12 2s2 2p6 3s2 26 2 12Mg + 2s2 2p6 MgO + H2SO4 → MgSO4 + H2O MgO + NaOH → no reaction Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4 SO3 + H2O → H2SO4 (sulfur(VI) oxide dissolves in water in dilute sulfuric acid) SO3 + 2NaOH → Na2SO4 + H2O Potassium has a larger atomic radius than sodium. The valence electron in potassium is further away from the nucleus and thus less strongly attracted by the nucleus. Hence, potassium loses its valence electron more readily than sodium, and is a better reducing agent.

The central O atom has 2 σ bond pairs (b.p.) and 2 lone pairs (l.p.) of electrons arranged in a tetrahedral manner. As l.p.–l.p. repulsion > l.p.–b.p. repulsion > b.p.–b.p. repulsion, by VSEPR. the H–O–H bond angle is compressed from ideal 109.5º to 105º. Carbon dioxide is a non-polar molecule. Despite the C=O bond being a polar bond due to the higher electronegativity of O compared to C, but due to the linear shape of the O=C=O molecule, the two bond dipoles cancel each other exactly. Non-polar CO2 molecules are held together by weak instantaneous dipole-induced dipole attractions. Thus, little energy is needed to separate them, giving a low boiling point. Since the reaction is endothermic, when the temperature is increased, the position of equilibrium shifts to the right, to absorb energy in attempt to counter the increase in temperature, leading to an increase in the equilibrium yield of CO.

T R Ea When temperature is increased, the average kinetic energy of the particles increases as seen in the shape of curve R compared to curve T. The frequency of collision increases. In addition, the number of particles with energy greater or equals to Ea increases as shown by the shaded region. Both factors causes the frequency of effective collision to increase and hence, the rate of reaction increases. 0

H2CO3(aq)  H+(aq) + HCO – 3(aq) H2CO3(aq)  2H+(aq) + CO 2 3 – (aq) ( ) ( aq) 2+ 2 3 c 23 H aq CO H CO aq K −      = ( )

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Nitrogen is being oxidised as the oxidation number of N increases from –3 in NH3 to 0 in N2, while hydrogen is being reduced as the oxidation number of H decrease from +1 in NH3 to 0 in H2. 2NH3 → N2 + 3H2 To catalyse the reduction of any oxides of nitrogen formed in the jet engine back to N2. As ammonia is less flammable than kerosene, there is less danger of a jet fire and impending explosion should there be a fuel leakage, making ammonia a safer fuel. As ammonia is a gas, which must be compressed and stored at high pressure, the tanks of ammonia must be thick-walled, making the tanks much heavier