Use this to mark your own attempt. Accept any correct alternative that answers the question as set. Marks are for the ideas, not the exact words. Unless stated, ecf (error carried forward) applies in calculations. Chermistry practice paper – not an official examination paper.
Total marks: 65 (Section A: 55 marks; Section B: one question of 10 marks)
| Part | Answer and mark points | Marks |
|---|---|---|
| 1(a) | solvent Reject: solute; solution; filtrate. | 1 |
| 1(b) | filtration Reject: distillation; evaporation; crystallisation; chromatography. | 1 |
| 1(c) | crystallisation Reject: evaporation to dryness (it would give a powder, not crystals); filtration; distillation. | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 2(a) | the nucleon number / the total number of protons and neutrons (in the nucleus) Accept: mass number. Reject: the number of protons; the number of electrons; “the mass” alone. | 1 |
| 2(b) | the proton number / the number of protons (in the nucleus) Accept: atomic number. Reject: the number of neutrons; the nucleon number. | 1 |
| 2(c) | neutrons: 39 − 19 = 20 [1]; electrons: 19 − 1 = 18 [1] (the ion has a charge of 1+, so it has lost one electron from the 19 in the atom) Accept ecf from wrong answers to (a) and (b) only if the method is correct. Reject: 19 electrons. | 2 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 3(a) | a pair of electrons shared between two atoms (accept: a shared pair of electrons) Accept: electrons shared between (non-metal) atoms. Reject: the transfer of electrons; the attraction between positive and negative ions. | 1 |
| 3(b) | methane and it has the lowest melting point / boiling point Reject: the name without a reason; the reason without the name; “it is a gas” alone. | 1 |
| 3(c) | • only the weak forces of attraction between the molecules (intermolecular forces) are overcome / broken (so the molecules separate) • the covalent bonds inside the molecules are strong / much more energy is needed to break them • Reject: covalent bonds are weak; “the bonds between the molecules are covalent”; ideas about ions or electrons. | 2 |
| 3(d) | it has no ions and no free electrons / no charged particles that are free to move; the molecules are neutral (uncharged) Accept: “no mobile charge carriers”; “no free ions or electrons to carry the charge”. Reject: “covalent bonds do not conduct”; “it has no electrons”; “it has no ions” on its own. | 1 |
| 3(e) | water or methane and its molecules contain atoms of different elements (hydrogen and oxygen / carbon and hydrogen) chemically bonded together Accept: “made of two (or more) different elements chemically combined”. Reject: iodine (an element: all its atoms are the same); a reason with no reference to different elements; “it is a molecule” (iodine is also a molecule). | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 4(a) | • zinc: hydrogen [1] • sodium carbonate: carbon dioxide [1] • magnesium oxide: the white solid dissolves / disappears (accept: a colourless solution forms) [1] • Accept formulae H2 and CO2. Reject: oxygen; carbon monoxide; “bubbles form” for magnesium oxide; “no change”; “no bubbles” or “no gas” for magnesium oxide (this repeats the table). | 3 |
| 4(b) | bubble the gas through limewater (aqueous calcium hydroxide) and it turns milky / cloudy (white precipitate) Both the reagent and the result are needed. Reject: “limewater goes white” with no reference to the gas being bubbled in; a lighted splint; damp litmus paper. | 1 |
| 4(c) | magnesium chloride Accept: MgCl2. Reject: magnesium chlorate; magnesium hydroxide; magnesium chlorine. | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 5(a) | • change 1: rate increases • change 2: rate increases • change 3: rate decreases • change 4: rate stays the same • change 5: rate increases • All five correct: 2 marks. Three or four correct: 1 mark. Fewer than three correct: 0. No mark for a row with two ticks. | 2 |
| 5(b) | • more particles per unit volume (the same number of particles in a smaller volume; the particles are closer together) • so the particles collide more frequently (higher collision frequency / more collisions per second) • Reject: “more particles” (the number of particles is the same); “the particles move faster” or “have more energy” (the temperature has not changed); “more collisions” with no reference to time or frequency. | 2 |
| 5(c) | exothermic and the temperature increases (from 25.0 °C to 26.2 °C) Reject: endothermic; a reason with no type of reaction. | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 6(a) | burning fossil fuels (coal, oil, natural gas) releases / produces carbon dioxide into the air Reject: it releases carbon monoxide; it releases methane; “it uses up oxygen”. | 1 |
| 6(b) | 414 − 317 = 97 ppm Reject: 97 with a different unit; 414 ÷ 317. | 1 |
| 6(c) | lightning (accept: lightning storms; thunderstorms) Reject: volcanoes; burning fossil fuels; car engines (not natural). | 1 |
| 6(d) | sugar cane (accept: sugarcane; sugar beet) Reject: “sugar” alone; wheat; potatoes. | 1 |
| 6(e) | the plant takes in carbon dioxide from the air by photosynthesis as it grows, which offsets / cancels out the carbon dioxide released when the bioethanol burns (petrol releases carbon dioxide that was stored underground for millions of years, with no offset) Reject: “bioethanol does not produce carbon dioxide”. | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 7(a) | • calcium ion (accept: Ca2+) [1] • a white precipitate that does not dissolve in excess sodium hydroxide or no precipitate with aqueous ammonia [1] (either result, correctly linked to calcium, earns the mark) • Reject: aluminium ion (aluminium hydroxide dissolves in excess aqueous sodium hydroxide); zinc ion; ammonium ion. No explanation mark if the cation is wrong. | 2 |
| 7(b) | • aluminium hydroxide dissolves in excess aqueous sodium hydroxide, but the precipitate does not [1] • aluminium ions form a white precipitate with aqueous ammonia, but no precipitate forms in test 2 [1] • Both ideas are needed for 2 marks. Reject: “aluminium hydroxide is not white” (the Data Sheet shows that it is white). | 2 |
| 7(c) | sulfate (accept: SO42−) Reject: sulfite; sulfide; carbonate. | 1 |
| 7(d) | barium sulfate (accept: BaSO4) Reject: barium nitrate; barium sulfite. | 1 |
| 7(e) | calcium sulfate (accept: CaSO4) Accept the spelling “sulphate”. Reject: calcium sulfite; calcium carbonate. | 1 |
| 7(f) | • correct formulae of all reactants and products [1]; balanced [1]; correct state symbols [1] • Missing or incorrect state symbols lose the third mark only. Correct formulae but unbalanced: 1 mark. A wrong formula loses the first mark; the balancing mark may still be awarded if the equation as written is balanced. • CaSO4(aq) + Ba(NO3)2(aq) → BaSO4(s) + Ca(NO3)2(aq) • or the ionic equation: Ba2+(aq) + SO42−(aq) → BaSO4(s). Reject: an equation using a barium compound other than barium nitrate (test 3 uses barium nitrate) for the formulae mark. | 3 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 8(a) | 207 + 16 = 223 | 1 |
| 8(b) | 44.6 ÷ 223 = 0.200 mol (ecf from (a)) | 1 |
| 8(c) | carbon is in excess: 3.00 ÷ 12 = 0.250 mol of carbon is present, but only 0.200 ÷ 2 = 0.100 mol is needed (ecf from (b)) The conclusion (carbon) and the supporting amounts are both needed. Reject: lead(II) oxide in excess. | 1 |
| 8(d) | 2 mol PbO form 2 mol Pb, so 0.200 mol Pb [1]; 0.200 × 207 = 41.4 g [1] (ecf from (b)) | 2 |
| 8(e) | 2 mol PbO react with 1 mol C: 0.200 ÷ 2 = 0.100 mol C reacts; 0.100 × 12 = 1.20 g C reacts [1]; 3.00 − 1.20 = 1.80 g [1] (ecf from (b)) Alternative: 3.00 ÷ 12 = 0.250 mol C present; 0.250 − 0.100 = 0.150 mol left; 0.150 × 12 = 1.80 g [1 for the amount left, 1 for the mass]. | 2 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 9(a) | • row 1 (it is a hydrocarbon): ethene, propene, poly(ethene) [1] • row 2 (it decolourises aqueous bromine): ethene, propene [1] • row 3 (it is a saturated compound): poly(ethene) [1] • row 4 (it has very large molecules): poly(ethene) [1] • 1 mark for each row. No mark for a row with a missing or an extra tick. | 4 |
| 9(b) | C5H10 Alkenes have the general formula CnH2n. Reject: C5H12. | 1 |
| 9(c) | a chain of four carbon atoms; the repeat unit –CH2–CH(C2H5)– shown twice, with the ethyl group on alternate carbon atoms of the chain [1]; continuation bonds at both ends and no C=C double bond [1]. Accept the ethyl group drawn above or below the chain, or as a displayed CH2CH3 group. Reject: a C=C bond left in the chain; a single repeat unit in brackets with n; ethyl groups on adjacent carbon atoms; the ethyl group inside the chain. | 2 |
| 9(d) | microorganisms (bacteria) cannot break them down / they are not biodegradable / the bonds in the polymer chain are strong (unreactive) Reject: “plastic is hard”; “it is made from oil”; “it is not natural” with no further idea. | 1 |
| 9(e) | C3H6 + Br2 → C3H6Br2 Accept a structural formula for the product, e.g. CH3CHBrCH2Br; state symbols are not required. | 1 |
| 9(f) | Two carbon atoms joined by a single bond; the O–H group on one carbon atom; every C–H and O–H bond drawn; each carbon has four bonds. Reject: CH3CH2OH (not displayed); C–H–O–H. | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 10(a) | • lithium, sodium and potassium (all three needed; accept Li, Na, K). Reject: rubidium (density 1.53 is greater than 1.00) • their densities are lower than that of water (1.00 g / cm3) / they are less dense than water. Accept: they have a low density | 2 |
| 10(b) | lithium hydroxide (accept LiOH). (2Li + 2H2O → 2LiOH + H2) Reject: hydroxide; lithium oxide; hydrogen hydroxide; water. | 1 |
| 10(c) | the reaction of potassium is more vigorous / faster / more violent. Accept: potassium melts / forms a ball; moves faster across the surface; burns with a (lilac) flame; the bubbles are produced faster. Reject: "potassium reacts" with no comparison; "less vigorous"; a difference in the products. | 1 |
| 10(d) | any value from 40 to 97 °C inclusive (the melting points fall down Group 1; the actual value is 63 °C). Reject: 98 or more; a value below 40. | 1 |
| 10(e)(i) | 2.8.1 (accept 2,8,1 or a correct diagram of electron shells). Reject: 2.1; 2.8.8.1; 11. | 1 |
| 10(e)(ii) | K2O. Reject: KO; K2O2. (Group 1 forms K+ and oxygen forms O2−.) | 1 |
| 10(f) | • 1 mark: two Li+ ions in square brackets with the charge + and no outer shell electrons (accept the first-shell pair shown) • 1 mark: O2− in square brackets with the charge 2− and eight electrons (six from oxygen plus two shown as the other symbol, one from each lithium) • Accept: all electrons as dots or all as crosses if the transfer is clear; the ions in any arrangement. Do not credit: a shared pair of electrons (covalent bonding); only one Li+; a missing or wrong charge loses the mark for that ion. | 2 |
| 10(g) | oxygen (atoms / molecules) gain electrons (from lithium atoms, to form oxide ions). Accept: the oxidation state of oxygen decreases from 0 to −2; each oxygen atom gains two electrons. Reject: "gains electrons" with no species named; oxygen loses electrons; "oxygen is removed / loses oxygen"; lithium gains electrons. | 1 |
| Part | Answer and mark points | Marks |
|---|---|---|
| 11(a) | • hydrogen (accept H2). Reject: steam; oxygen • 48 cm3 (accept 47 to 50 cm3, read from the face of the piston nearer the gas, or the centre of the piston). Reject: no unit or a wrong unit; 60 | 2 |
| 11(b) | copper and a reason: no gas is collected (0 cm3) / no change / it does not react with steam. Both are needed. Reject: iron (the next least reactive); a reason with no metal named. | 1 |
| 11(c) | magnesium oxide (accept MgO). (Mg + H2O → MgO + H2) Reject: magnesium hydroxide; magnesium; magnesium hydride. | 1 |
| 11(d) | calcium is the most reactive (first / above magnesium). Reject: between magnesium and zinc; below magnesium; "calcium is reactive". | 1 |
| 11(e)(i) | • ticks in row 2 (tap water, open) and row 4 (damp air, open) only. Both rows are needed and no others. Row 1 has no water; row 3 has no oxygen (boiled water, oil layer). | 1 |
| 11(e)(ii) | boiling removes dissolved oxygen and the oil stops oxygen (air) reaching the water, so there is no oxygen (for rusting). Accept: oxygen is needed for rusting and none is present. Reject: there is no water; oil stops the iron reacting; the oil is a barrier to water. | 1 |
| 11(f) | • two shared pairs of electrons (a double bond: two dots and two crosses) drawn in the overlap of the two circles • two non-bonding pairs (lone pairs) drawn on each atom, outside the overlap, so that each atom has eight outer shell electrons including the shared pairs; dots and crosses used for the two different atoms • Accept all electrons as dots or all as crosses if the double bond is clear. Do not credit: a single shared pair; a triple bond; electrons drawn only on one atom; unpaired outer electrons only. | 2 |
| 11(g) | oxidation: magnesium changes from 0 to +2 and reduction: hydrogen changes from +1 to 0. All three values are needed for the mark. Reject: +2 to 0; 0 to −2; a hydrogen value of +2 or −1. | 1 |