1. The document provides answers to chemistry questions from an IGCSE revision guide, covering topics like the structure of atoms, compounds, chemical equations, and calculations involving moles.
2. Sections include quick checks with multiple choice or short answer questions, as well as more in-depth explanations and worked examples.
3. Tables, diagrams, and definitions are referenced to further illustrate chemical concepts and solutions steps.
1. The document provides answers to chemistry questions from an IGCSE revision guide, covering topics like the structure of atoms, compounds, chemical equations, and calculations involving moles.
2. Sections include quick checks with multiple choice or short answer questions, as well as more in-depth explanations and worked examples.
3. Tables, diagrams, and definitions are referenced to further illustrate chemical concepts and solutions steps.
1. The document provides answers to chemistry questions from an IGCSE revision guide, covering topics like the structure of atoms, compounds, chemical equations, and calculations involving moles.
2. Sections include quick checks with multiple choice or short answer questions, as well as more in-depth explanations and worked examples.
3. Tables, diagrams, and definitions are referenced to further illustrate chemical concepts and solutions steps.
1. The document provides answers to chemistry questions from an IGCSE revision guide, covering topics like the structure of atoms, compounds, chemical equations, and calculations involving moles.
2. Sections include quick checks with multiple choice or short answer questions, as well as more in-depth explanations and worked examples.
3. Tables, diagrams, and definitions are referenced to further illustrate chemical concepts and solutions steps.
outer shell of 8 electrons, which is a stable arrangement Section 6
Answers to questions 2 as for sodium and chlorine on page 25, but with one middle shell less for each atom 3 regular arrangement of alternating positive and Quick checks for 6.1 1 6.02 × 1023 2 a 71 g b 35.1 g 3 a 4 b 0.075 c 0.04 negative ions held in a lattice 4 a and b: as for magnesium oxide for 6.2 1 a CH b C6H6 2 both NO2 The example answers, marks awarded, and comments Questions on Section 2 and magnesium chloride on pages 25 and 26, but calcium has an for 6.3 1 512 g 2 12 g 3 68 g 4 4.76 g of MgO, 5.24 g of CO2 that appear in this book were written by the authors. In Core curriculum 1 a simple distillation b fractional distillation extra inner shell of 8 electrons 5 a NaOH b AlCl3 c Mg(OH)2 for 6.4 1 a 0.125 mol/dm3 b 6 mol/dm3 2 a 4 dm3 b 0.02 examination, the way marks would be awarded to answers c crystallization d fractional distillation e ltration 2 a Bacteria for 4.4 1 Each shares its one electron. 2 Each atom has gained dm3 or 20 cm3 3 a 0.15 b 0.1 4 a 112g b 0.56g 5 0.1 dm3 or like these may be different. and soil particles are larger than the gaps in the limestone, but an outer shell of 8 electrons (or 2 in H2). 3 Your diagram should 100 cm3 6 0.015 dm3 or 15 cm3 water particles are smaller. b i condenser ii in the beaker be like the diagram for methane on page 28, but with chlorine for 6.5 1 a 4.5 dm3 or 4500 cm3 b 2.4 dm3 or 2400 cm3 Section 1 iii It is higher. 3 a See table on page 22. b i insoluble ii Add water atoms (7 outer-shell electrons) in place of hydrogen atoms. 2 1.2 dm3 or 1200 cm3 3 125 dm3 of both Quick checks (and heat) to dissolve the soluble compound; pass the mixture 4 lattice with regular arrangement of hydrogen molecules for 6.6 1 100% 2 75% 3 80% 4 18.2 tonnes 5 83.3% for 1.1 1 a because the water particles can slide past each 5 The forces between molecules are weak. 6 a and b: see page 28. through lter paper in a lter funnel, and collect the ltrate (the other b because the water particles can’t move any closer 7 solution of the compound) in a suitable container. iii See page 9. Questions on Section 6 2 because the gas particles in the air can be squeezed a lot 4 a See example 1 on page 11. b i F ii G iii G H Extended curriculum 1 a 0.3g of CaCO3 = 0.003 moles. That closer 3 Diffusion: sugar particles collide with water particles, Extended curriculum 1 a (ii) b B c Use a locating agent. needs 0.006 moles of HCl for complete reaction. But bounce away, and in this way spread through the water. d A, 0.65; B, 0.4 e Look up the Rf values of amino acids in the H 0.005 moles of HCl are used. So CaCO3 is in excess. b volume for 1.2 1 a because the vibrations of the particles get larger solvent f Solubility is different in different solvents. for 4.5 1 covalent bonds 2 a Both have covalent bonding. of CO2 = 0.06 dm3 or 60 cm3 2 a Repeat titration without the b The particles will vibrate so much that the structure breaks Alternative to practical 1 a A, thermometer B, beaker C, b Molecules contain small numbers of atoms, macromolecules indicator, evaporate to remove some water, allow to cool to down. 2 a gas b 130 °C 3 The heating curve will be like tripod D, condenser b to cool and condense the vapour contain millions. 3 The weak forces between layers allow them obtain crystals, dry the crystals. b i 0.056 ii 0.028 iii 9.016 g the one on page 3, but with the horizontal sections at 130 °C c Measure its boiling point. 2 a to prevent ink spreading up the to slide over each other, so graphite is soft and slippery; the free iv 42.8% 3 a 0.048 moles b 0.024 moles c 2PbCO3.Pb(OH)2 (melting point) and 240 °C (boiling point). 4 sublimation paper b 1 and 3 c 4; two spots electrons allow it to conduct. 4 Similar bonding and structure to 4 a i See denition on page 39. ii the number of particles in for 1.3 1 They follow a zig-zag random path, changing diamond, but different from that in graphite. 1 mole of a substance b CH4 and SO2; there are 0.125 moles of direction in response to bombardment by water particles. for 4.6 1 It is the attraction between metal ions and the sea of each c i Ca, 0.12 moles; H2O, 0.2 moles ii calcium, because 0.2 2 because they are continually bombarded by air particles Section 3 free electrons. 2 It forms a giant regular lattice. 3 They contain moles of water reacts with 0.1 moles of calcium iii 0.8 g for 1.4 1 When they meet, they combine to form a white Quick checks free electrons that can move, carrying current. 5 a 0.926 moles b 1.389 moles c 0.926 moles cloud of ammonium chloride, which is easy to see. for 3.1 1 a neutron b electron c proton d electron 2 a 3 d Ratio Fe : O : H2O is 2 : 3 : 2 e Fe2O3.2H2O 6 a 0.04 moles 2 a chlorine, since it has the larger relative molecular mass b 4 c 7 d 73Li 3 The atoms are: a sodium, with 11p 11e 12n Questions on Section 4 b i 0.03 moles ii 0.05 moles iii 0.02 moles c equation 3 b raise the temperature b calcium, with 20p 20e 20n c iron, with 26p 26e 30n Core curriculum 1 a Check your drawing against the diagram (mole ratio 2:1) 7 1 (one) for 3.2 1 atoms of the same element, that have the same Questions on Section 1 for H2O on page 28. b P2O3 2 i C ii E iii F iv E v D vi B proton number but a different nucleon number Core curriculum 1 a See the diagrams on page 1. b i They vii A, D and F 3 a The layers of atoms can slide over each other, only vibrate. ii They move around, and slide past each other. 2 a 6, 7, and 8 b 126C (called C-12) c 146 C 3 It is unstable and making it slippery. b Each atom is bonded to four others, with Section 7 decays, giving out radiation. Quick checks c They come close together, with forces of attraction between the strong covalent bonds. for 3. 3 1 b (2 + 8 +1) 2 Show three shells, with 2 electrons in for 7.1 1 a and e Yes, metals contain electrons free to move. particles d the gas state e The particles move around faster, with Extended curriculum 1 the inner shell, 8 in the second, and 6 in the outer shell. Cl b Yes, ions in solution are free to move. c and d No, there are more energy. They collide more often and bounce further away. 3 Note: for the drawings in this question you can show electrons no ions in sugar. 2 a ions not free to move b Melt it, or dissolve f There is plenty of space between the particles, so they can be in (pairs as on page 19.) a Show one shell with 1 electron in it. O C it in water. pushed into a smaller volume by applying pressure. g The particles b Show two shells: 2 electrons in the inner shell, 1 in the for 7.2 1 a It carries current into and out of the liquid, during are close together but can slide over each other, allowing the second. c Show four shells: 2 electrons in the inner shell, 8 in Cl electrolysis. b the liquid which is electrolysed 2 a connected liquid to take any shape. 2 a The crystal dissolves and the particles the second and third shells, and 1 in the fourth shell. to the positive terminal of the battery b anode 3 metal at spread by diffusion: they collide with water molecules and bounce for 3.4 1 a i lithium ii uorine iii chlorine b uorine cathode, non-metal at anode 4 a potassium and chlorine away. b i regular, with particles close together ii They only vibrate. 2 from left to right, top to bottom: good; sodium chloride and chlorine: both have 7 electrons in their outer shells b hydrogen and chlorine 3 a ammonia, hydrogen chloride, and the gases in air (or similar); silicon dioxide; ions and electrons; good 2 phosphorus, 2 + 8 + 5 3 a helium b phosphorus 4 a helium for 7.3 1 Na+ (l) + e → Na (l); 2Cl– (l) → Cl2 (g) + 2e b i ammonium chloride ii white c It shows that gas particles b nitrogen c magnesium d chlorine e calcium 3 A tiny % of water molecules is ionised to H+ and OH ions. (ammonia and hydrogen chloride) have spread from the ends of 5 a 1 b 2 + 8 + 2 c 2 + 8 + 18 + 8 + 1 for 7.4 1 Copper ions are removed when copper forms at the the tube, and meet at X, where they react. d They collide with Section 5 cathode. 2 a As copper ions are removed, more form at the gas particles in air and bounce away again. e Ammonia will Quick checks Questions on Section 3 anode. b The anode loses copper. For each atom it loses, one is diffuse all through the tube – but no white solid will form. 3 for 5.1 1 a carbon and hydrogen, ratio 1:4 b nitrogen and Core curriculum 1 a i A and E ii C iii C iv B b He c Missing deposited on the cathode. 4 a i boiling ii the line would not be horizontal b i close 2 hydrogen, ratio 1:3 c iron and sulfur, ratio 1:1 d calcium, words in order: protons, neutrons, radioactive, energy 2 a atoms for 7.5 1 Use a nickel anode, the spoon as cathode, and a together ii far apart iii random and fast iv no v yes carbon and oxygen, ratio 1:1:3 2 methane + oxygen → of the same element, with different numbers of neutrons b Br-79 solution of a soluble nickel compound as electrolyte. 2 In both, Extended curriculum 1 a i See page 1. ii non-existent iii They carbon dioxide + water 3 1:2:1:2 has 35e, 44n, 35p; Br-81 has 35e, 46n, 35p 3 a the number of metal atoms are lost from the anode, and deposited on the move freely and fast. b i hydrogen, helium, oxygen, chlorine for 5.2 1 H2 (g) + Cl2 (g) → 2HCl (g) protons in the nucleus of the atom b Your diagram should show cathode. 3 A dilute solution would give oxygen, not chlorine. ii The lower its relative molecular mass, the faster a gas will diffuse. 2 a 2Mg (s) + O2 (g) → 2MgO (s) 3 electrons in the outer shell, and 8 in the middle shell. c 15 4 by dissolving it in cryolite 5 Al3+ + 3e → Al; 2O2– → O2 + 4e c It will diffuse twice as fast as oxygen. d It is between 32 and 71. b 4Fe (s) + 3O2 (g) → 2 Fe2O3 (s) Extended curriculum 1 a 40Ar: 18p, 18e, 22n; 40Ca: 20p, 3 2H2O2 (l) → 2H2O (l) + O2 (g) 20e, 20n; 44Ca: 20p, 20e, 24n b i They have the same number Questions on Section 7 for 5.3 1 the average mass of its naturally-occurring isotopes, Section 2 of protons but different numbers of neutrons. ii They do not relative to the mass of a carbon-12 atom 2 a 48 b titanium Core curriculum 1 a PbBr2 b giant, ionic c i B ii platinum Quick checks have the same number of protons. c + 8 + 2 2 a 2 protons, iii to make the ions free to move iv bromine at anode; lead at 3 40 4 It is the average value for two isotopes. 5 a 17 b 32 for 2.1 1 weighing balance for the salt, measuring cylinder for 2 electrons, and 2 neutrons more b + 8 + 2 3 a B is 23 Na, cathode 2 a cathode b to be the electrolyte c chromium 11 c 106 6 It is an ionic compound. water 2 pipette 3 a 2500 g b 500 g 4 a 500 cm3 b 2000 cm3 C is 40 Ar, D is 31 P 3–, E is 27 Al 3+ b B – the same number of protons 3 a cathode b i Copper is deposited on it. ii It dissolves. 18 11 13 for 5.4 1 100 g 2 a 160 g b 180 g c 400 g 5 a 2 dm3 b 0.5 dm3 c 1.5 dm3 d 0.5 dm3 Extended curriculum 1 a Melt the compound, or dissolve 3 a copper(II) carbonate → copper(II) oxide + carbon dioxide for 2.2 1 a It is impure. b below –114.3 °C 2 food additives, it in water. b Positive ions move to the cathode, negative ions Section 4 b copper(II) oxide 20 g, carbon dioxide 11 g medical drugs, vaccines to the anode. c i 2Cl– → Cl2 + 2e ii Cu2+ + 2e → Cu for 2.3 1 a the substance you dissolve b the liquid you Quick checks d i Oxygen forms rather than chlorine. ii 4OH– → 2H2O + O2 + 4e for 4.1 1 The iron and sulfur atoms in it are held together by Questions on Section 5 dissolve the substance in 2 fractionating column and e Lithium is more reactive than hydrogen, copper is less chemical bonds. 2 looks different, the iron and sulfur atoms in Core curriculum 1 a 2H2 + O2 → 2H2O thermometer added for fractional distillation 3 a to separate reactive than hydrogen. f i It loses copper atoms as ions, so it are chemically bonded, it cannot be separated into iron and b N2 + 3H2 → 2NH3 c I2 + Cl2 →2ICl the liquid from any solution of your choice b to separate any it dissolves. ii Cu→ Cu2+ + 2e iii oxidation 2 a splitting by sulfur by physical means 3 See the table on page 23. 4 add d 2P + 3Cl2 → 2PCl3 2 a 6 g b 97.5% mixture of two or more miscible liquids 4 As the crystals form, electricity b hydrogen ion H+, chloride ion Cl , hydroxide ion OH– substances to turn into an alloy 3 a 2Mg (s) + O2 (g) → 2 MgO (s) b 40 c i 4.0 g ii 1.6 g any impurities are left behind in the liquid. c i hydrogen: 2H+ + 2e– → H2 ii reduction: gain of electrons for 4.2 1 bonding: how atoms are joined; structure: how 4 a 217 b 20.1 g of mercury, 1.6 g of oxygen for 2.4 1 Each dye has different solubility in the solvent and d i oxygen ii chlorine 3 a i 2H+ + 2e– → H2 ii 2Cl– → Cl2 + 2e– attraction to the paper. So the dyes move at different speeds up the bonded atoms are arranged 2 ionic: electrons transferred; iii Na+ and OH ions are left in solution. b i It kills microbes / germs / the paper. 2 the yellow dye 3 Each amino acid has a unique Rf covalent: electrons shared 3 a regular arrangement of particles bacteria. ii ammonia / hydrogen chloride / margarine value in a given solvent. 4 as a single spot (showing up after a 4 molecule 5 a lattice of silver ions, Ag+, in a sea of electrons locating agent is used) 5 0.5625 for 4.3 1 loses one electron, because that leaves it with a full