Difficulty tags below are based on the examiner’s notes for each question/sub-part.
(a) Recognised by a minority ? challenging.
(b) Correct for a small number; Equation I commonly chosen incorrectly.
(c)(d)(f) Correct for a large number of candidates.
(e) Answered reasonably well.
(a)(i)–(v) Largely correct; occasional wrong symbols (e.g. O, Li, Be).
(a)(vi) Reasonably well answered; O often seen as an incorrect answer.
(b)(i) Many omitted reference to atoms.
(b)(ii) Many good calculations; common error: averaging 10 and 11 to give 10.5 or rounding to 11/11.0.
(a)(i) Common error: only 7 outer-shell electrons on oxide ions (two Na donate one each).
(a)(ii) Reasonably well; some gave equations instead of a formula.
(b) Reasonably well; frequent non-bonding electron mistakes on O and C.
(c)(i) Many mixed up ionic vs covalent descriptions; some misread comparison with CO2.
(c)(ii) Covalent bonding chosen as often as the correct answer.
(a) Most stated catalysts increase rate, but missed that catalysts remain unchanged.
(b)(i) Mass decrease only from leakage/escape; oxygen gas; some wrote “oxygen given off” without credit.
(b)(ii) Rate depends on concentration; fastest at start since [H2O2] highest.
(b)(iii) Many omitted that rate becomes zero when H2O2 is used up.
(c) Frequent partial/incorrect particle-collision statements; activation energy often missing.
(d) Calculation: common error multiplying moles of O2 by 24 or 16 instead of 32.
(e) Catalyst amount does not affect mass of O2 formed; depends on amount of H2O2.
(f) Poor performance on HgO decomposition equation: wrong formulas (e.g. O not O2), unbalanced, reactants/products swapped.
(a)(i) Repeated learned definition of electrolysis; vague/incomplete statements.
(a)(ii) Few stated both: graphite inert & good conductor.
(a)(iii) Reasonably well; wrong charge on H+ or H formula common.
(a)(iv)(v) Mixed success; “ion”/“electron/proton” common incorrect.
(a)(vi) Aqueous halide electrolysis (dilute vs concentrated) confused; oxygen as anode product for dilute KBr.
(b)(i) Reasonably well.
(b)(ii) Many misconceptions: cryolite changes MP of Al2O3 (fixed); cryolite stated as a conductor rather than solvent.
(b)(iii) Few mentioned carbon anode conversion to CO2.
(c)(i) Minority knew fuel-cell reaction same as H2 combustion; H and O sometimes given as products; H2O only occasionally correct.
(c)(ii) Vague answers; needed comparison to petrol in vehicles and reference to H/O.
(a)(i) Mostly balanced; occasional stray “7” before O2.
(a)(ii) Many misunderstandings: oxidation number stated without compound; FeO seen as Fe2O3.
(b)(i) Reasonably well; some cited enzyme denaturation wrongly.
(b)(ii) Slightly easier than (b)(i); error: “fewer molecules” reference.
(c) Few wrote correct (NH4)2SO4; extra products (H2/H2O) given.
(d)(i) Few knew all nitrates are soluble.
(d)(ii) Poorly answered; ionic equation issues (states/species); PbSO4 errors common.
(d)(iii) Filtration first then crystallisation; many gave washing/drying route or lacked procedural detail.
(a)(i) Quite well answered; some focused on substitution rather than UV need.
(a)(ii) Reasonably well; branched isomers/double drawings common.
(b)(i) Many gave structural names instead of molecular formulae.
(b)(ii) Very well answered; spelling “carboxylic” challenging.
(b)(iii) Descriptions rather than observations common (“precipitate forming”).
(b)(iv) Reasonably well; bracket/–n not needed in polymer drawings; connectivity issues common.
(b)(v) Challenging; common answers: esters or named polymers (Terylene, PET, polyamides).
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