Many candidates showed good core Chemistry knowledge and wrote clear English; most responded to all questions.
Common needs: precise chemical terms (atoms/ions/molecules), correct qualitative tests, filtration diagrams, meaning of ‘properties’, molecular vs displayed formulae, and blast-furnace stages.
Frequent issues: vague harms (e.g., “toxic”), confusing nitrate harms with nitrogen oxides, writing equations when names requested, missing H2 ion formula, and weak descriptions of crystallisation/drying.
Most parts well answered; part (d) (test for chromium(III) ion) was least well done.
Key notes: (a) count atoms in a molecule (don’t give ions); (b) bromine is diatomic; (c) chloride ion forms by gaining an electron; (d) identify Cr3+ (not Cu2+/K+); (e) CaCO3 ? CO2 on heating; (f) photosynthesis makes O2 (not CO2).
Good on (b)(i), (b)(iii), (c), (d). Weaker in (a) filtration diagram, (b)(ii) sulfate ion name, and (e) harms of sewage/nitrates.
Watch for: draw filter paper inside funnel; distinguish filtrate vs residue; SO42? name; Na electronic configuration with correct inner electrons and 1+ charge; oxygen essential for aquatic life; give specific harms (eutrophication/oxygen depletion), not vague “toxic”.
Mixed performance; basic errors seen in (b)(i) and (c).
Notes: correct dot-and-cross for NH3; give specific adverse effects of NO2 (e.g., respiratory irritation/acid rain), not just “factories”; recognise NO2 is acidic oxide (not basic) due to non-metal oxide nature.
Best-answered question overall.
Highlights: (a) two properties of transition elements (coloured compounds, catalysts, variable oxidation states etc.); (b) AgCl insoluble; (c)(i) pathway diagram with formulae in boxes, reactants left/products right; (c)(ii) exothermic = energy of reactants > energy of products; (d) correct reactivity order (don’t swap Fe/Ni); (e) correct empirical formula calculation.
Generally well answered; part (a) weakest (meaning of “properties”).
Key points: describe ionic properties (high mp, conduct when molten/aqueous); (b) electrolysis products at electrodes (hydrogen at negative, iodine at positive); (b)(ii) anode = positive electrode; (c) calculate protons/neutrons carefully; (d)(i) balance equations (iodine as I2), (ii) recognise displacement not neutralisation, (iii) chlorine colour “yellow-green”.
One of the least-well answered questions; only (a)(i)(ii), (c) and (d)(i) were generally strong.
Focus: (a)(iii) molecular formula (don’t write structural/‘C4H7OH’ guesses); (a)(iv) specific distillation steps separating crotyl alcohol/water; (b) fermentation conditions (yeast + correct temperature range); (c) correct general formula (alkenes vs alkanes); (d)(ii) displayed formula (choose one type, correct H count); (d)(iii) chlorine reacts with alkanes in light; (d)(iv) balance oxygen properly (avoid HO2, CO/C as products).
Also among the least-well answered.
Essentials: (a)(i) name ore = hematite; (a)(ii) blast-furnace steps (C + O2 ? CO2; CO2 + C ? CO; Fe2O3 + CO ? Fe + CO2; CaCO3 ? CaO + CO2; CaO + SiO2 ? slag), (a)(iii) KMT for liquids — arrangement and motion (slide past each other); (b) oxidation shown by iron losing electrons/oxygen gain; (c)(i) define ‘hydrated’ precisely; (c)(ii) conditions for rusting; (d)(i) filtration separates solid from solution; (d)(ii) describe safe crystal drying to ‘point of crystallisation’, then cool/dry.
Well answered by many; strong performance in (a)(i), (b)(i), (c)(i), (c)(iii).
Reminders: (a)(i) read volume at 2 min (~44 cm?3; endpoint recognition), (a)(ii) draw correct line with initial gradient and cap at 44 cm?3;; (b)(i)(ii) larger pieces/lower temperature ? slower rate (not “takes longer” as rate statement); (c)(i) equation completion; (c)(ii) formula for ion present in all acids (H+); (c)(iii) pH of NaOH solution >7 (avoid pH 4); (c)(iv) methyl orange is yellow in alkali (not orange/red).
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