AQA-8464C2H-W-MS-NOV20.

Question Answers Extra information Mark AO / Spec. Ref. 01.1 C3H8 + 5 O2 → 3 CO2 + 4 H2O allow multiples 1 AO2 5.1.1.1 5.7.1.3 01.2 (bubble gas through) lime water turns milky / cloudy / white or white precipitate forms MP2 is dependent upon correct response in MP1 allow (bubble gas through) calcium hydroxide (solution) 1 1 AO1.2 5.8.2.3 01.3 C3H6 1 AO2 5.1.1.1 5.7.1.4 01.4 burning / lit splint burns with a (squeaky) pop sound MP2 is dependent upon correct response in MP1 allow flame do not accept glowing splint allow pops 1 1 AO1 5.8.2.1 01.5 bromine (water) (colour change) orange (to) colourless do not accept bromide allow 1 mark for colourless (to) orange ignore clear 1 1 1 AO1 5.7.1.4 Total 9 MARK SCHEME – GCSE COMBINED SCIENCE: TRILOGY – 8464/C/2H – JUNE 208 Question Answers Mark AO / Spec. Ref. 02.1 Level 3: The method would lead to the production of a valid outcome. All key steps are identified and logically sequenced. 5–6 AO3 5.6.1.2 Level 2: The method would not necessarily lead to a valid outcome. Most steps are identified, but the plan is not fully logically sequenced. 3–4 Level 1: The method would not lead to a valid outcome. Some relevant steps are identified, but links are not made clear. 1–2 No relevant content 0 Indicative content: • use a measuring cylinder / pipette / burette to measure 50 cm3 of sodium thiosulfate • use a different measuring cylinder / pipette / burette to measure 10 cm3 of hydrochloric acid • start the timer when the acid is added • record the temperature of the solution after the acid is added • stop the timer when the cross is no longer visible • record the temperature of the solution at the end of the reaction • calculate the mean temperature of the reaction • repeat the experiment at different temperatures • use the same concentration of sodium thiosulfate and same concentration of hydrochloric acid • use the same volume of sodium thiosulfate and the same volume of hydrochloric acid • describe how to heat the thiosulfate / acid solutions MARK SCHEME – GCSE COMBINED SCIENCE: TRILOGY – 8464/C/2H – JUNE 209 Question Answers Extra information Mark AO / Spec. Ref. 02.2 (change in mass of gas = ) 0.15 and (time =) 2 (rate of reaction =) 0.15 2 0.075 (g/min) ignore signs allow correct use of incorrectly determined values for mass and / or time 1 1 1 AO2 5.6.1.1 5.6.1.4 MARK SCHEME – GCSE COMBINED SCIENCE: TRILOGY – 8464/C/2H – JUNE 2010 02.3 curve starts at same point, to the left and steeper line levels at − 0.35 g the curve below can be awarded 2 marks 1 1 AO2 5.6.1.1 5.6.1.2 5.6.1.4 Total 11 MARK SCHEME – GCSE COMBINED SCIENCE: TRILOGY – 8464/C/2H – JUNE 2011 Question Answers Extra information Mark AO / Spec. Ref. 03.1 microbes chemicals allow bacteria / pathogens 1 1 AO1 5.10.1.3 03.2 anaerobic digestion 1 AO1 5.10.1.3 03.3 (decrease = ) 6.7 (billion) (% decrease =) 6.7 8.0 × 100 = 84 (%) alternative approach: (% now used =) 1.3 8.0 × 100 (1) = 16.25 (1) (% decrease =) 84 (%) (1) allow correct use of an incorrect value for decrease in plastic bag use allow 83.75 / 83.8 (%) allow 83.75 / 83.8 (%) 1 1 1 AO2 5.10.2.2 MARK SCHEME – GCSE COMBINED SCIENCE: TRILOGY – 8464/C/2H – JUNE 2012 03.4 respiratory problems or acid rain allow named respiratory conditions eg asthma allow breathing problems allow consequences of acid rain eg kills aquatic life or damages limestone buildings allow smog 1 AO1 5.9.3.2 03.5 (increased) more traffic (decreased) improved efficiency of car engines allow more cars allow use of catalytic converters allow more electric / hybrid cars allow lower temperature of car engines allow more use of public transport allow more people walk / cycle ignore better designed engines