Question Library

This is a popular question among the candidates. In part (a), majority of the candidates listed the two gaseous fuels produced from coke. In part (b), majority of the candidates could not differentiate between thermosets and thermoplastics. They could not give one example thermosets and thermoplastics. In part (c), majority of the candidates stated the method of collecting gases which are denser than air. Also, majority of them named two gases that could be used to perform the fountain experiment in the laboratory. In part (d), majority of the candidates stated two compounds that could be used to test for water. They gave three disadvantages of hard water. The expected answers include: (a)(i) - producer gas -water gas (ii) Water gas (iii) It is because producer gas contains about 67% / more non-combustible nitrogen and 33% / less of combustible carbon (II) oxide while water gas consist of equal amounts of combustible carbon (II) oxide and hydrogen. (iv) - 2C(s) + O\(_2\) + 4N\(_2\) → 2CO + 4N\(_2\) - C(s) + H\(_2\)O(g) → CO(g) + H\(_2\)(g) (b)(i) Thermoplastics can be softened by heat and remoulded while thermosets cannot be softened by heat and remoulded once they are formed or set. (ii) Examples: Thermosets: Urea-methanal Polyvinyl chloride (p.v.c.) Bakelite Thermoplastics: Polyethene Polypropene/ Polyamide Nylon Perspex Polystyrene Terylene (iii)- good insulators - can be recycled/softened and reshaped - are non-biodegradable - can be tailor – made to exact requirements - resistance to corrosion - water-proof (c)(i) Upward displacement of air / downward delivery (ii) - hydrogen chloride - ammonia - sulphur (IV) oxide (iii) The gases are highly/very soluble in water. (d)(i) - copper (II) tetraoxosulphate (VI)/CuSO\(_4\) - cobalt (II) chloride/CoCl\(_2\) (ii) - wastes soap/forms scum/costs a lot of money to soften/does not readily lather with soap - causes furring/scales in kettles / boilers - cannot be used in dyeing / tanning

(a) A compound is defined as a substance containing two or more elements / different atoms chemically combined (in a fixed proportion by mass) (b) - high temperature - catalyst - high pressure (c)- Iron - Nickel - Palladium - Platinium - Rhodium (d)(i) Zn(s) + 2AgNO\(_3\)(aq) → Zn(NO\(_3\))\(_{2(aq)}\) + 2 Ag(s) (ii) I. AgNO\(_3\) / Ag + is reduced II. Zn is oxidized (e) \(\frac{16}{8}\)O = 90%, \(\frac{18}{8}\)O = 10% Relative atomic mass = \(\frac{\frac{16 \times 90}{199} + \frac{18 \times 10}{100} }{(16 \times 0.9) + (18 \times 0.1)}\) = \(\frac{1440}{100} + \frac{180}{100}\) = 14.4 + 1.8 = 16.2 (f) - haematite (Fe\(_2\)O\(_3\))/ Iron (III) oxide - magnetite (Fe\(_3\)O\(_4\))/Iron (II) Iron (III) oxide - limonite Fe\(_2\)O\(_3\).nH\(_2\)O/Iron (III) oxide hydrate(accept FeO(OH).nH\(_2\)O) - iron pyrites FeS/Iron (II) Sulphide - Siderite/spathic iron ore /FeCO\(_3\)/Iron (II) trioxocarbonate (IV) (g) (i) It is the use of biological processes / organisms / system to manufacture useful products (ii) - garri, fufu, kenkey, bread - bio-gas, - alcoholic beverages (beer, whisky, burukutu, gin, etc) - drugs (vaccines, hormonal, antibiotics) - enzymes - biodegradable plastics - pests control - organic fertilizers (h) An element is defined as a substance containing only one type of atom / substance which cannot be broken down into a simpler one. (i) - land fill sites / compost - marshes/swampy area - rice (paddy) fields - bacteria - natural gas - biomass burning - crude oil/petroleum - decay of organic matter - raising of livestock - coal mine (j) The molecules are held together by van der Waal’s forces . The larger the atom, the greater the van der Waal’s forces/increase in molecular mass and hence the higher the boiling point.

(a) When a standard hydrogen electrode is connected to a standard zinc half-cell the emf measured is 0.76V. The negative sign implies the flow of electrons from the zinc electrode to the hydrogen electrode. (b)(i) Anode/ Zn electrode Zn(s) → Zn\(^{2+}\)\(_{(aq)}\) + 2e\(^-\) / Zn(s) – 2e\(^-\) → Zn\(^{2+}\)\(_{(aq)}\) Cathode/Cu electrode Cu\(^{2+}\) \(_{(aq)}\) + 2e\(^-\) → Cu(s) (ii) Zn(s) + Cu\(^{2+}_{(aq)}\) → Zn\(^{2+}_{(aq)}\) + Cu(s) (iii) Anode/Zn electrode – oxidation Cathode/Cu electrode – reduction (iv) Eocell = Eored – Eooxid = (0.34 V) – (-0.76 V) = + 1.10 V (c) (i) - Textile - Brewery - Plastic - Refinery - Cement - Food [e.g flour, tea, sugar, etc] - Pharmaceutical - Fertilizer - Metallurgical - Paint - Soap and detergent - Ceramic - Rubber - Glass - Etc (ii) - nearness to raw materials / feed stock - nearness to market - labour supply - transportation - nearness to power supply - government policy - away from residential area - availability of water (iii)- Improvement in the standard of living - Employment opportunities - Development in the community - Pollution: air, noise, water, thermal - Social effects (d)(i) Hydrogen peroxide reduces silver oxide to silver metal/H2O2is oxidized to O2 A + H\(_2\)O\(_2\)\(_{(aq)}\) → 2Ag\(_{(s)}\) + H\(_2\)O\(_{(l)}\) + O\(_{2(g)}\) (ii) Hydrogen peroxide reduces chlorine to hydrochloric acid/H\(_2\)O\(_2\) is oxidized to O\(_2\) Cl\(_{2(g)}\) + H\(_2\)O\(_{2(aq)}\) → 2HCl\(_{(aq)}\) + O\(_{2(g)}\) (e) - colourless - odourless - slightly lighter / less dense than air - slightly soluble in water - low melting (-210\(^{o}\)C/ 63 K)/low boiling point (-196\(^{o}\)C/ 77 K)

(a)(i) Heat the iron strongly in a combustion tube until it is red hot. Generate steam by boiling water in a flask. Pass the steam over the red-hot iron. Hydrogen gas would be given off. Collect the hydrogen gas formed over water. (ii) 3Fe(s) + 4H\(_2\)O\(_{(g)}\) Fe\(_3\)O\(_{4(s)}\) + 4H\(_{2(g)}\) (iii) - from water gas / Bosch process - from methane - by electrolytic method - from catalytic cracking of petroleum products (b) (i) It favours the backward reaction / Equilibrium position shifts to the left (ii) Equilibrium position shifts to the right / favours the forward reaction (iii) Equilibrium position shifts to the right / favours the forward reaction. (c)(i) Condensation polymerization is defined as the linking together of monomers (with two different functional groups) to form a polymer with the elimination of a small molecule. (ii) - Nylon/polyamide - Terylene - Silk - Wool - Cellulose - Proteins - Starch - Dacron/polyester - Phenol methanal - Urea methanal - Melamine methanal (iii) - CH\(_3\)COOC\(_2\)H\(_5\) (d) (i) Allotropy is defined as the existence of two or more forms of an element in the same physical state. (ii)- diamond - graphite (iii) Diamond Graphite - jewellery - lubricant - drilling - black pigment in paints - cutting - electrical conductor for electrodes - abrasive - lead pencil - making of bearings - alloying - pivot support - neutron moderators - dies for drawing wires -lining of crucibles (e) N\(_2\)O O\(_2\) - pleasant smell - odourless - no reaction with NO - reacts with NO - produces N\(_2\)/gas with heated copper - produces no N\(_2\)/gas with heated copper

(a) (i) - Bauxite (ii) - Iron (III) oxide - Silica / silicon (IV) oxide - Calcium trioxosilicate (IV) (iii)- Graphite / Carbon (iv) - uses less energy / power / electricity - conserves resources of ores / bauxite - less expensive/reduces cost (v)- Carbon anode reacts with oxygen - Gas / CO\(_2\) given off (b)(i) Q = It Q = 0.75 x 64 x 60 = 2880C (iv) Number of Faradays = 288,000 96,500 = 2.984 charge = + 3 (c) (i) Vanadium (V) oxide (ii) 400 – 500\(^o\)C / 673 – 773 K (iii) the yield decreases (d)(i) - by boiling - by addition of(calculated amount of) Ca(OH)\(_2\) – Calcium hydroxide/slaked lime - by addition of washing soda/Na\(_2\)CO\(_3\) - by addition of NaOH\(^-\) Sodium hydroxide/Caustic Soda - by ion exchange/ permutit (ii)- Ca(HCO\(_3\))\(_2\)\(_{(aq)}\) boil CaCO\(_{3(s)}\) + H\(_2\)O\(_{(l)}\) + CO\(_{2(g)}\) - Ca(HCO\(_3\))\(_{2(aq)}\) + Ca(OH)\(_{2(aq)}\) → 2CaCO\(_{3(s)}\) + 2H2O\(_{(l)}\) - Ca(HCO\(_3\))\(_2\)\(_{(aq)}\) + Na\(_2\)CO\(_{3(s)}\) → CaCO\(_{3(s)}\) + 2NaHCO\(_{3(aq)}\) - Ca(HCO\(_3\))\(_{2(aq)}\) + 2NaOH\(_{(aq)}\) → 2NaHCO\(_{3(aq)}\) + Ca(OH)\(_{2(aq)}\) - Ca(HCO\(_3\))\(_{2(aq)}\) + 2NaR → CaR\(_2\) + 2NaHCO\(_{3(aq)}\)

(a)(i) States that atoms, molecules/ions / particles / reactants involved in a chemical reaction must collide before reaction can take place. (ii) When temperature is increased/decreased the reacting molecules gain / lose kinetic energy and move faster / slower. Frequency of collision and effective collision increases/decreases therefore rate of reaction increases/decreases. (The explanation must correspond to score) (ii) C\(_6\)H\(_5\)OH\(_{(aq)}\) + 3O\(_{2(g)}\) → 3H\(_2\)O\(_{(l)}\) + 2CO\(_{2(g)}\) From the equation 1 mole of ethanol requires 3 x 22.4 dm\(^3\) of oxygen 2.5 mols = \(\frac{2.5 \times 3 \times 22.4}{1}\) = 168.0 dm\(^3\) (c) (i) Esterification is the reaction between an alkanol and alkanoic acid to produce an alkanoate / ester (and water in the presence of a mineral acid.) (ii) - used as solvents (e.g. for paints, nail, varnishes, lacquer, adhesives and cellulose nitrates) - used in perfumes/cosmetics - used in (artificial) flavouring for foods - production of soap - plasticizers (iii) ethanol / C\(_2\)H\(_5\)OH and sodium ethanoate (CH\(_3\)COONa) / potassium ethanoate(CH\(_3\)COOK) (d)(i) Tin – coated plate (ii) Zinc is more reactive than tin / higher in the electrochemical series than tin. When the tin coated plate is exposed, the plate goes into solution / corrodes. In zinc coated (galvanized) plate, it is the zinc that dissolves / corrodes hence protecting the plate better and zinc coated plate does not corrode.

(a) (i) gas > liquid > solid / gas, liquid, solid (ii) solid > liquid > gas / solid, liquid, gas (c) (i) (I) 0 to +2 (II) +1 to 0 (ii)(I) Magnesium / Mg (II) Hydrogen / H\(^+\) / HCl (iii) Hydrochloric acid / HCl (d) (i) Evaporation Boiling - occurs on the surface of Liquid - occurs at the entire length of Liquid - occurs slowly - occurs rapidly - occurs at any temperature - occurs at specific temperature - produces cooling - does not produce cooling - occurs using internal energy/is Spontaneous - requires an external source of Heat / not spontaneous - bubbles are not seen - bubbles are seen (ii) The temperature required to boil the water decreases / boils at temperature lower than 1000 C (e) The equilibrium constant k, indicates the extent to which a reaction will proceed / it gives an idea of where the equilibrium lies / when k is large, more of the products are formed / when k is small, less of the products are formed. (f) C\(_3\)H\(_7\)COOH: butanoic acid (CH\(_3\))3COH: 2 – methyl propan-2-ol (g) Functional groups are atoms or groups of atoms that are responsible for particular chemical properties and reactions of organic compounds. (h) Solids in liquids Gases in liquid - solubility increases with temperature - solubility decreases as temperature increases - it is not affected by change in pressure / does not have any significant effect - is greatly affected by pressure, increases with increase in pressure - increasing and decreasing of pH affects the solubility - pH does not affect them - depends on the nature of solute and solvent - depends on nature of gas and solvent (i) 2F\(_{2 (g)}\) + 2H\(_2\)O\(_{(l)}\) → 4HF\(_{ (aq)}\) + O\(_{2 (g)}\) (j) is the number of replaceable hydrogen ions in a molecule of an acid / number of ionisable hydrogen atoms in one molecule of acid.

(a)(i) ratio of atoms C = \(\frac{0.48}{12}\) = 0.04, H= \(\frac{0.08}{1}\) = 0.08, Cl = \(\frac{1.42}{35.5}\) = 0.04 Divide by the smallest number \(\frac{0.04}{0.04}\): \(\frac{0.08}{0.04}\) : \(\frac{0.04}{0.04}\) 1 : 2 : 1 Empirical formula = CH\(_2\)Cl (ii) Molecular formula = (Empirical formula)n 99 = (CH\(_2\)Cl)n 99 = (12 + (2 x 1) + 35.5)n 99 = 49.5n n = \(\frac{99}{49.5}\) = 2 molecular formular = C\(_2\)H\(_4\)Cl\(_2\) / (CH\(_2\)Cl)\(_2\) (b) - in its molten form / solution conducts electricity - has strong electrostatic forces - has high melting / boiling points - is highly soluble in water (c) (i) & (ii) Reaction co-ordinate (d) (i) Naphtha Accept kerosene / Diesel (ii) Fractional distillation (iii) - Ethene - Propene (iv) Catalytic cracking whereby long-chain hydrocarbons (in the naphtha fraction) are broken down into small organic molecules Conditions are 600\(^o\) C and Al\(_2\)O\(_2\)\(_{(s)}\) / SiO\(_2\)\(_{(s)}\) as catalyst (v) - Polyethene - Polypropane

(a) (i) The cations and anions attract the polar water molecules the energy released as the ion-dipole forces are formed provides the energy to break the electrostatic forces of attraction between the oppositely charged ions in the potassium chloride. OR The water molecules split KCl into free ions with a release of energy known as lattice energy. The free ions are hydrated/surrounded by water molecules. This is known as the hydration energy. (ii) More energy is needed to overcome the ion-ion attraction hence the dissolution process is endothermic / OR lattice energy is greater than hydration energy. (b) (i) Magnesium is more reactive than iron therefore magnesium reacts preferentially / acts as a sacrificial anode. (ii) Iron oxidizes to Fe\(^{2+}\) by oxygen and water to give Iron (II) hydroxide / Fe\(^{2+}\) and OH\(^-\) formed. Further oxidation gives hydrated Iron (III) oxide / Fe2O\(_3\).xH\(_2\)O (iii) Presence of (dissolved) oxygen / air (c) (i) It is a reaction that occurs without being driven by some outside / external force. (ii) - G must be negative - the products are more random, more disorganized than the reactants / entropy of products is greater than entropy of reactants / entropy must increase (iii) Sodium is in Group I and is more reactive metal than calcium that is in Group II. / sodium is more electropositive than calcium / higher in the reactivity series (iv) (d) Mr (PbCO\(_3\)) = 207 + 12 + 16(3) = 267g mol\(^{-1}\) (e) (i) van der Waal’s forces (ii) hydrogen bonding

(a) - addition of alum / addition of coagulating agent - sedimentation - filtration - disinfection / chlorination / addition of chlorine (b) (i) - iron (III) oxide - silicon (IV) oxide / sand - trioxosilicates (IV) (ii) because aluminium oxide has too high a melting point to eletrolyse on its own / bauxite has low silica content (iii) - Alumina and molten cryolite Melted and electrolysed Cell with carbon electrodes Molten aluminium produced at the base of cell. siphoned off / removed at the base (c) (i) A fine chemical industry is the one that manufactures chemicals in smaller quantities / amounts for specific use with high level of purity (ii) Fine chemical Heavy chemical - they are produced in smaller quantities - they are produced in larger quantities - they are highly pure - they are not pure - they are final products - they are intermediate products - they are more costly / expensive - less costly / less expensive (d) (i) C\(_{(s)}\) + O\(_{2(g)}\) (ii) Amount of coal burnt = \(\frac{5.4}{12}\) mol\(^{-1}\) = 0.45mol From the equation of the reaction moles of O\(_2\) used = moles of C burnt = 0.45 1 moles of O\(_2\) = 22.4 dm\(^3\) 0.45 mol O\(_2\) = 22.4 x 0.45 = 10.1dm\(^3\) (e) - platinum - carbon

(a) (i) - sulphur (IV) oxide /SO\(_2\) - nitrogen (IV) oxide / NO\(_2\) - nitrogen (II) oxide / NO - carbon (II) oxide / (CO) - methane / CH\(_4\) (ii) Large lumps have smaller surface area to volume ratio than the broken pieces which has a greater surface area / increased exposed surface area. This makes the broken pieces to collide more frequently. OR The greater the rate of frequency of successful collisions, the greater the rate of reaction hence for the pieces of coal more reactant particles are exposed at the surface thereby increasing the frequency of successful collisions between reactant particles. (iii) methane gas / CH\(_4\) (iv) coke / carbon (b) (i) - chlorine dioxide / (ClO\(_2\)) - sulphur (IV) oxide SO\(_2\) - hydrogen peroxide / H\(_2\)O\(_2\) - sodium peroxide Na\(_2\)O\(_2\) (ii) - Manganese (IV) oxide / MnO\(_2\) - Lead (IV) oxide / PbO2\(_2\) (iii) - CaO - MgO - Na\(_2\)O - K\(_2\)O (iv) Aluminium oxide (Al\(_2\)O\(_3\)), ZnO, PbO, SnO\(_2\), SnO, PbO\(_2\) (v) - nitrogen (IV) oxide / NO2\(_2\) (c) (i) (ii) Redox reaction (iii) Because Iron (II) ions is oxidized to iron (III) ions / chlorine is reduced to chloride ions / chlorine gas oxidizes iron (II) ions to iron (III) ions and in the process chlorine is reduced to chloride ions / oxidation number of iron increases from +2 to +3 while that of chlorine decreases from 0 to -1. (d) (i) A - delivery tube B - Calcium oxide / CaO / quicklime (ii) (iii) Ammonia (iv) To prevent the (round bottom) flask from cracking / to prevent the water / steam formed from condensing into the hot glass flask. (v) (I) Drying agent / To dry the gas (II) Upward delivery / downward displacement of air (e) - Paraffin wax - Asphalt / bitumen

Rough Tree 1st Titre 2rd Titre 3rd Titre Final reading cm\(^3\) 15.60 31.10 45.50 15.60 Initial reading cm\(^3\) 0.00 15.60 31.10 0.00 Volume of the acid cm\(^3\) 15.50 15.50 15.40 15.60 (a) Average Titre = \(\frac{15.50 + 15.40 + 15.60}{3}\) cm\(^3\) = \(\frac{46.50}{3}\)cm\(^3\) = 15.50 cm\(^3\) (b)(i) Concentration of B in moldm\(^{-3}\) 250cm\(^3\) of B contains 480g of FeCl\(_2\) 100 cm\(^{-3}\) of B will contain \(\frac{4.80}{250}\) x 1000g = 19.2 gdm\(^{-3}\) Concentration of B in moldm\(^{-3}\) ? = \(\frac{\text{conc. in gdm}^{-3}}{\text{molar mass}} = \frac{19.2 gdm^{-3}}{127 gmol^{-1}}\) = 0.151 mol dm\(^3\) Concentration of A in mol dm\(^{-3}\) = ? \(\frac{C_AV_A}{C_BV_B} = \frac{n_A}{n_B}\) C\(_A\) = Molar concentration in moldm\(^{-3}\) of KMnO\(_4\) = ? V\(_A\) = Volume of KMnO\(_4\) used = 15.50cm\(^3\) n\(_A\) = 1 C\(_B\) = Molar concentration of FeCl\(_{2(aq)}\) = 0.151 moldm\(^{-3}\) V\(_B\) = Volume of FeCl\(_{2(aq)}\) = 25.00 cm\(^3\) = \(\frac{C_A \times 15.50 cm^3}{0.151 mold dm^{-3} \times 25.00 cm^3}\) = \(\frac{1}{5}\) C\(_A = \frac{0.151 \times 1 \times 25.00}{5 times 15.50} = \frac{3.775}{77.50}\) = 0.0487 (3sf) C\(_A\) = 0.0487 moldm\(^{-3}\) (ii) Number of moles of Fe\(^{2+}\) in the volume of B pipetted? 1000 cm\(^3\) of B contains 0.151 moles of Fe\(^{2+}\) 25cm of B will contain \(\frac{0.151}{1000} \times 25\) moles = 0.0003775 mole of Fe\(^{2+}\)

TEST OBSERVATION INTERFERENCE (a) Sample C + distilled water + shaking Resulting solution + litmus paper Sample C dissolved to form a blue/greenish solution Solution turns blue litmus paper red Solution is acidic (I) 1st portion + NaOH\(_{(aq)}\) in drops Then in excess Blue precipitate formed Precipitate insoluble in excess Cu\(^{2+}\) is present (ii) 2nd portion NH\(_4\)OH\(_{(aq)}\) in drops Then in excess Light blue precipitate formed Precipitate dissolve in excess to form a deep blue solution Cu\(^{2+}\) is confirmed (iii) 3rd portion + AgNO\(_{3(aq)}\)+ NCl\(_{(aq)}\) White precipitate formed Precipitate insoluble Cl\(^{-1}\) or CO\(_{3^{2-}}\) or S\(^{2-}\) or SO\(_3^2\) Cl\(^{2-}\) is present (b)(i) Sample D + distilled water touching or feeling the test tubes Sample D dissolved to form a colourless solution Test tube feels cold on touching Dissolution is endothermic (ii) D\(_{(aq)}\) = HCl\(_{(aq)}\) Effervescence (bubbling) occurs, a colourless, odourless gad evolved Gas turned lime water milky CO\(_{2(g)}\) from CO\(_{3^{2-}}\) or HCO\(_3^-\)

(a) Observation made when 2cm\(^3\) of bench H\(_2\)SO\(_4\) was added to 2cm\(^3\) of barium chloride solution. H\(_2\)SO\(_{4(q)}\) + BaCl\(_{2(aq)}\) \(\to\) BaSO\(_{4(s)}\)(white) + 2HCl\(_{(aq)}\) White precipitate of BaSO\(_4\) Barium tetraoxosulphate(VI) is formed (b) Observation made by the addition of dilute hydrochloric acid to 1g of powered iron (III) sulphide (FeS) 2HCl\(_{(aq)}\) + FeS\(_{(s)}\) \(\to\) FeCl\(_{(aq)}\) + H\(_2\)S\(_{(g)}\) Effervescence (bubbling) occurs or evolution of a gas with a smell of rotten eggs and a green solution is formed. (c) Observation made by the addition of 2cm\(^3\) of dillute hydrochloric acid to 1g of iron filings and allowed to stand for sometime Effervescence or evolution of colourless, odourless gas noticed with the formation of light green solution that will turn brown after sometime.

(a) Observation made when 2cm\(^3\) of bench H\(_2\)SO\(_4\) was added to 2cm\(^3\) of barium chloride solution. H\(_2\)SO\(_{4(q)}\) + BaCl\(_{2(aq)}\) \(\to\) BaSO\(_{4(s)}\)(white) + 2HCl\(_{(aq)}\) White precipitate of BaSO\(_4\) Barium tetraoxosulphate(VI) is formed (b) Observation made by the addition of dilute hydrochloric acid to 1g of powered iron (III) sulphide (FeS) 2HCl\(_{(aq)}\) + FeS\(_{(s)}\) \(\to\) FeCl\(_{(aq)}\) + H\(_2\)S\(_{(g)}\) Effervescence (bubbling) occurs or evolution of a gas with a smell of rotten eggs and a green solution is formed. (c) Observation made by the addition of 2cm\(^3\) of dillute hydrochloric acid to 1g of iron filings and allowed to stand for sometime Effervescence or evolution of colourless, odourless gas noticed with the formation of light green solution that will turn brown after sometime.