CIE 9701 AS Chemistry P2 高频定义解释

CIE 9701 AS Chemistry P2 高频定义解释：频率优先版

使用顺序：先背 Frequency 高的行，再用 Sources 回到原题核对题干。统计范围为 2020-2025 AS Paper 2 mark schemes，N = 44；同一卷同一点只计 1 次。Full-mark wording 是可直接背诵的答案骨架；Sources 已按最新到最旧排列，MS 文件名通常把 _qp_ 换成 _ms_。no 2020-2025 P2 MS hit 表示这条是 syllabus / core review point，放在 appendix，不参与高频排序。

考试定位：CIE 9701 AS Chemistry Paper 2 是 AS Level Structured Questions 理论卷；考试时间 1 h 15 min，60 marks。题目覆盖 AS syllabus 的 physical / inorganic / organic chemistry，常见题型是 definitions, explanations, calculations, equations, data interpretation 和 organic mechanisms。

Official syllabus: Cambridge 9701 Chemistry syllabus 2025-2027; Paper 2 is a written paper, 1 hour 15 minutes, 60 marks.

答题核心：按 MS 关键词拿分。定义题写必要限定词；解释题按原因 → 作用对象 → 结果写完整因果链；计算题保留单位和合适 s.f.；有机机理题要画清 curly arrows 的起点、终点、电荷和中间体。

Highest-Frequency First

Frequency	Papers	Chapter	Point	Full-mark wording	Sources
64%	28/44	14-17	mechanism curly-arrow rule	1. curly arrows start at a lone pair/electron pair/bond/negative charge 2. arrow points to the atom or bond receiving the electron pair 3. for bond breaking, arrow goes from the bond to the atom receiving the electrons	9701_w25_qp_24 Q3(b)(ii); 9701_s25_qp_22 Q3(a)(ii); 9701_m25_qp_22 Q4(b)(i); +25 additional hits
59%	26/44	3	bonding diagrams: metallic / dot-and-cross / coordinate	1. for dot-and-cross diagrams, show outer-shell electrons only and use different symbols for electrons from different atoms 2. covalent bonds are shared pairs; coordinate/dative bonds have both electrons in the shared pair donated by one atom/species 3. metallic bonding diagrams need a lattice/regular arrangement of positive ions/cations and delocalised electrons 4. for NH₄Cl, show ionic attraction between NH₄⁺ and Cl⁻, four N-H covalent bonds in NH₄⁺, and one N→H coordinate bond / one N-H bonding pair from N	9701_s24_qp_23 Q4(a); 9701_w20_qp_21 Q3(a)(i); 9701_s20_qp_22 Q1(b); +23 additional hits
50%	22/44	3	simple molecular boiling/melting	1. greater number of electrons in the molecules 2. stronger instantaneous dipole-induced dipole forces / van der Waals’ forces between molecules 3. more energy is needed to overcome the intermolecular forces	9701_w20_qp_23 Q4(a)(iii); 9701_w20_qp_21 Q4(a)(iii); 9701_s20_qp_21 Q1(b)(i); +21 additional hits
43%	19/44	3 / 13	σ and π bonds / orbital overlap / hybridisation	1. a σ bond is formed by direct/head-on/end-on overlap of orbitals between the bonding atoms 2. a π bond is formed by sideways/lateral overlap of adjacent p orbitals 3. single bond = 1σ; double bond = 1σ + 1π; triple bond = 1σ + 2π 4. common hybridisation: sp gives linear/triple-bond centres; sp² gives trigonal planar/C=C centres; sp³ gives tetrahedral/saturated carbon or ammonium centres	9701_s24_qp_23 Q1(a)(ii); 9701_s24_qp_21 Q4(b)(i-ii); 9701_s22_qp_21 Q2(a); +16 additional hits
41%	18/44	21	oxidation/reduction route	1. choose reagent and conditions from the functional group 2. acidified K₂Cr₂O₇/KMnO₄ with distil/reflux for alcohols/aldehydes 3. NaBH₄ or LiAlH₄ for carbonyl reduction	9701_w20_qp_21 Q3(c)(i); 9701_s20_qp_22 Q5(a); 9701_m20_qp_22 Q3(a)(i); +22 additional hits
36%	16/44	all	equations / state symbols	1. use correct formulae 2. balance the equation 3. include charges where needed 4. include state symbols when the question asks for them	9701_s20_qp_22 Q1(e)(ii); 9701_s20_qp_21 Q2(a)(i); 9701_s20_qp_21 Q1(c)(i); +20 additional hits
36%	16/44	1	IE trend explanation	1. compare nuclear charge/proton number 2. compare shielding and distance from the nucleus 3. link these to nuclear attraction for the outer electron	9701_w20_qp_22 Q1(b)(iv); 9701_w20_qp_21 Q1(c); 9701_w20_qp_21 Q1(b); +24 additional hits
36%	16/44	22	IR absorption identification	1. quote the absorption range in cm⁻¹ 2. state the bond responsible 3. state the functional group responsible 4. use presence/absence of O-H, C=O, C≡N etc. as evidence	9701_w20_qp_21 Q3(c)(v); 9701_s20_qp_21 Q6(e); 9701_m20_qp_22 Q3(d)(iii); +17 additional hits
32%	14/44	9	Period 3 melting point structure	1. identify the structure: simple molecular / giant metallic / giant covalent as appropriate 2. simple molecular substances: only weak intermolecular / van der Waals’ forces are overcome, so less energy is needed 3. giant metallic/covalent substances: many strong metallic/covalent bonds or attractions must be overcome/broken, so more energy is needed	9701_w21_qp_23 Q3(a)(i); 9701_w21_qp_21 Q3(a)(i); 9701_w20_qp_22 Q2(f); +12 additional hits
32%	14/44	6	reducing agent	1. donates electrons and is oxidised	9701_w20_qp_22 Q4(b)(iii); 9701_w20_qp_21 Q3(c)(ii); 9701_m20_qp_22 Q2(c)(ii); +14 additional hits
32%	14/44	3	metallic bonding / conductivity	1. giant metallic lattice / regular arrangement of positive ions/cations surrounded by delocalised electrons 2. many strong electrostatic attractions between cations and delocalised electrons / strong metallic bonds need more energy to overcome, so melting point is high 3. delocalised electrons are free to move through the structure and carry charge	9701_w24_qp_21 Q3(a)(iii); 9701_s22_qp_23 Q1(f)(ii); 9701_s22_qp_22 Q1(a); +5 additional hits
30%	13/44	11	chlorine disproportionation / water purification	1. cold dilute NaOH: Cl₂ + 2NaOH → NaCl + NaClO + H₂O 2. hot concentrated NaOH: 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O 3. in water: Cl₂ + H₂O ⇌ HCl + HOCl 4. HOCl / ClO⁻ kills bacteria/microbes; this is the active species in water purification 5. chlorine disproportionates because Cl is both oxidised and reduced	9701_m25_qp_22 Q3(b); 9701_s23_qp_22 Q2(d); 9701_s21_qp_23 Q1(c); +10 additional hits
27%	12/44	14	major product / carbocation stability	1. major product forms via the more stable carbocation/intermediate 2. more alkyl groups give greater positive inductive effect/electron donation 3. positive charge is spread/stabilised more	9701_s20_qp_21 Q5(d)(ii); 9701_s20_qp_21 Q5(d)(i); 9701_m20_qp_22 Q3(c)(iii); +30 additional hits
27%	12/44	7	Kp / Kc expression and units	1. for aA + bB ⇌ cC + dD, write Kc = [C]^c[D]^d / ([A]^a[B]^b) 2. for gases, write Kp = p(C)^cp(D)^d / (p(A)^ap(B)^b) 3. products over reactants; powers are stoichiometric coefficients 4. omit pure solids/liquids; derive units from the final expression	9701_s23_qp_23 Q4(b)(ii); 9701_s21_qp_23 Q2(c)(iii); 9701_m20_qp_22 Q1(f)(ii); +9 additional hits
25%	11/44	12	SO₂ acid rain	1. SO₂ reacts with water to form H₂SO₃ 2. SO₂ / H₂SO₃ can be oxidised to H₂SO₄ 3. these acids cause acid rain	9701_w21_qp_23 Q1(d)(ii); 9701_w21_qp_21 Q1(d)(ii); 9701_s20_qp_22 Q2(d); +3 additional hits
25%	11/44	6	oxidising agent	1. accepts electrons and is reduced	9701_m21_qp_22 Q4(c)(i); 9701_m20_qp_22 Q2(c)(ii); 9701_m20_qp_22 Q2(b)(i); +11 additional hits
25%	11/44	7	Bronsted acid / strong vs weak acid	1. acid = proton/H⁺ donor 2. strong acid fully dissociates/fully ionises in aqueous solution/water 3. weak acid partially dissociates/partially ionises in aqueous solution/water	9701_w20_qp_23 Q2(b)(i); 9701_w20_qp_22 Q3(d)(ii); 9701_w20_qp_21 Q2(b)(i); +11 additional hits
23%	10/44	14	alkene test	1. bromine water / Br₂(aq) is decolourised from orange/brown to colourless	9701_s22_qp_22 Q6(a); 9701_s21_qp_21 Q5(c)(ii); 9701_s21_qp_21 Q4(b); +7 additional hits
23%	10/44	17	2,4-DNPH test	1. 2,4-DNPH gives a red/orange/yellow precipitate with carbonyl compounds (aldehydes/ketones)	9701_s21_qp_23 Q4(b); 9701_w20_qp_22 Q4(c); 9701_s20_qp_21 Q6(d); +10 additional hits
23%	10/44	19	nitrile hydrolysis to carboxylic acid / carboxylate	1. acid hydrolysis: RCN + 2H₂O + HCl/H⁺ → RCOOH + NH₄Cl/NH₄⁺ 2. alkaline hydrolysis: RCN + 2H₂O + NaOH → RCO₂Na + NH₄OH/NH₃; acidification gives RCOOH if required 3. heat/reflux with dilute acid or aqueous alkali 4. the nitrile carbon becomes the carboxyl carbon, so the carbon chain length does not change during hydrolysis	9701_s25_qp_24 Q4(d)(i); 9701_s22_qp_22 Q5(c)(ii); 9701_w20_qp_21 Q3(c)(iv); +7 additional hits
20%	9/44	8	frequency of effective collisions	1. rate increases/decreases with the frequency of successful/effective collisions per unit time	9701_s22_qp_21 Q1(g); 9701_m22_qp_22 Q2(b)(iii); 9701_m21_qp_22 Q1(c)(ii); +7 additional hits
20%	9/44	11	NOₓ / atmospheric pollution	1. NOₓ forms when N₂ and O₂ react at high temperature in an internal combustion engine / lightning 2. NO/NO₂ reacts with oxygen and/or water/moist air to form HNO₂/HNO₃ and cause acid rain 3. NO/NO₂ can act as a homogeneous catalyst in SO₂ oxidation to SO₃ and is regenerated 4. NO₂/NOₓ reacts with unburned hydrocarbons/VOCs to form photochemical smog / PAN	9701_s24_qp_23 Q2(d)(i-ii); 9701_s23_qp_21 Q5(b)(i-iii); 9701_s22_qp_21 Q2(b)(i-ii); 9701_s20_qp_22 Q2(d); +5 additional hits
20%	9/44	9	Period 3 chloride hydrolysis	1. SiCl₄ + 2H₂O → SiO₂ + 4HCl 2. PCl₅ + 4H₂O → H₃PO₄ + 5HCl 3. include state symbols / acidic products if the question asks	9701_w21_qp_23 Q3(b)(ii); 9701_w21_qp_21 Q3(b)(ii); 9701_w20_qp_22 Q3(b)(ii); +12 additional hits
20%	9/44	17	Tollens / Fehling distinction	1. aldehydes reduce Tollens’ reagent to a silver mirror/grey precipitate 2. aldehydes reduce Fehling’s solution to a brick-red precipitate 3. ketones show no visible change	9701_m22_qp_22 Q4(a)(i); 9701_m21_qp_22 Q4(b); 9701_w20_qp_22 Q4(a)(iv); +6 additional hits
20%	9/44	2	relative atomic/isotopic/molecular mass	1. mass / weighted average mass of atom, isotope or molecule 2. compared with 1/12 of the mass of a carbon-12 atom or the unified atomic mass unit	9701_w22_qp_21 Q1(a)(ii); 9701_s20_qp_23 Q2(a); 9701_s20_qp_22 Q1(a); +6 additional hits
18%	8/44	14	free-radical substitution	1. initiation: homolytic fission in UV light forms halogen radicals 2. propagation 1: a halogen radical removes H from an alkane to form an alkyl radical and HCl/HBr 3. propagation 2: the alkyl radical reacts with Cl2/Br2 to form a halogenoalkane and regenerate a halogen radical 4. termination: two radicals combine to form a stable molecule	9701_w24_qp_21 Q2(b)(iii); 9701_m21_qp_22 Q2(g)(i); 9701_s20_qp_23 Q4(b)(ii); +22 additional hits
18%	8/44	13	structural isomerism	1. same molecular formula but different structural formulae	9701_w22_qp_22 Q3(a)(ii); 9701_w22_qp_21 Q3(d)(iv); 9701_s21_qp_23 Q5(d); +6 additional hits
18%	8/44	4	ideal gas equation calculation	1. use pV = nRT with Pa, m³ and K	9701_m21_qp_22 Q1(b)(ii); 9701_m21_qp_22 Q1(b)(i); 9701_w20_qp_22 Q3(d)(iii); +3 additional hits
18%	8/44	5	enthalpy change of formation	1. enthalpy/energy change when one mole of compound/substance is formed 2. from its elements in their standard states	9701_w21_qp_22 Q1(b); 9701_s20_qp_21 Q3(a); 9701_m20_qp_22 Q1(g)(ii); +6 additional hits
18%	8/44	8	temperature effect	1. higher temperature means particles have greater average kinetic energy, so a greater proportion of particles have E ≥ Ea 2. frequency of successful/effective collisions increases	9701_s25_qp_21 Q3(a)(ii); 9701_s24_qp_23 Q2(b)(ii)
16%	7/44	12	photochemical smog / PAN	1. unburned/unburnt hydrocarbons / VOCs react or combine with NO and/or NO₂ 2. PAN / peroxyacetyl nitrate / peroxyacetylnitrate is formed 3. PAN is a component of photochemical smog	9701_s25_qp_23 Q3(a)(ii); 9701_s24_qp_23 Q2(d)(ii); 9701_s22_qp_21 Q2(b)(i); 9701_m22_qp_22 Q2(d)(ii); +3 additional hits
16%	7/44	13	stereoisomerism	1. same structural formula but different spatial arrangement of atoms/groups	9701_w22_qp_23 Q5(a)(iii); 9701_w22_qp_21 Q5(a)(iii); 9701_w21_qp_22 Q3(e)(iv); +8 additional hits
16%	7/44	3	coordinate/dative bond definition	1. a covalent bond/shared pair is formed 2. both electrons in the shared pair are donated by one atom/species	9701_s21_qp_21 Q2(a)(i); 9701_m21_qp_22 Q2(e)(i); 9701_s20_qp_21 Q1(b)(ii); +4 additional hits
14%	6/44	11	AgNO₃ / NH₃ test	1. acidify with dilute HNO₃, then add aqueous AgNO₃ 2. Cl⁻ gives a white precipitate, soluble in dilute NH₃ 3. Br⁻ gives a cream/off-white precipitate, partly/slightly soluble in concentrated NH₃ 4. I⁻ gives a yellow precipitate, insoluble in concentrated NH₃	9701_w22_qp_21 Q2(c); 9701_s22_qp_22 Q2(d); 9701_m20_qp_22 Q2(c)(i); +6 additional hits

Formula / Expression Table From Recent P2

统计口径：2020-2025 AS Paper 2 QP/MS，N = 44；本表只收录题面或 MS 中明确出现、要求写出或要求代入的公式/表达式。Frequency 按命中卷数统计；具体来源列的是可直接用文件名复制检索的 QP stem。

Frequency	Area	Formula / expression to write	MS-ready use	Sources
27% 12/44	Kp / Kc overall	General equilibrium: aA + bB ⇌ cC + dD Kc = [C]^c[D]^d / ([A]^a[B]^b) Gas equilibrium: aA(g) + bB(g) ⇌ cC(g) + dD(g) Kp = p(C)^cp(D)^d / (p(A)^ap(B)^b) One example: H₂(g) + I₂(g) ⇌ 2HI(g): Kc = [HI]² / ([H₂][I₂]); Kp = p(HI)² / (p(H₂)p(I₂))	1. [X] means equilibrium concentration of X 2. p(X) means equilibrium partial pressure of gas X 3. powers are the balanced-equation coefficients a, b, c, d 4. omit pure solids/liquids; derive units from the final expression	CIE_化学AS_A2_计算公式_答案版.xlsx AS rows 13-14; 9701_s23_qp_23 Q4(b)(ii); 9701_w21_qp_22 Q1(c)(i-ii); +10 additional hits
18% 8/44	ideal gas	pV = nRT; therefore n = pV / RT, p = nRT / V, and Mr = mass / n	1. use Pa, m³ and K with R = 8.31 2. convert cm³/dm³/kPa before substitution 3. check whether the question asks for pressure, amount, volume or Mr	9701_w23_qp_23 Q3(d)(i); 9701_w23_qp_21 Q3(d)(i); 9701_w22_qp_22 Q2(c)(ii); 9701_m21_qp_22 Q1(b)(i-ii); 9701_w20_qp_22 Q3(d)(iii); +3 additional hits
11% 5/44	partial pressure	mole fraction = amount of gas / total amount of gas partial pressure = mole fraction × total pressure	1. calculate mole fraction before partial pressure 2. keep pressure units consistent with the Kp units requested	9701_s24_qp_23 Q2(c)(ii-iii); 9701_w23_qp_22 Q2(c); 9701_w21_qp_22 Q1(c)(ii); 9701_s21_qp_23 Q2(c)(ii)
11% 5/44	bond energy	ΔH = Σ(bond energies broken) - Σ(bond energies formed)	1. bonds broken are positive 2. bonds formed are subtracted 3. multiply each bond energy by the number of that bond in the balanced equation	9701_s22_qp_23 Q3(a)(ii); 9701_w21_qp_22 Q1(c)(iii); 9701_m21_qp_22 Q2(c)(i); +3 additional hits
11% 5/44	M+1 carbon count	number of C atoms = ([M+1]⁺ abundance / M⁺ abundance) × 100 / 1.1	1. use the [M+1]⁺ peak caused mainly by ¹³C 2. rearrange if the [M+1]⁺ abundance is the unknown 3. round to a whole number of carbon atoms	9701_w25_qp_21 Q4(c)(iii); 9701_s23_qp_23 Q5(c); 9701_s23_qp_21 Q4(b)(iii); +1 additional hits
9% 4/44	calorimetry	q = mcΔT ΔH = -q / n	1. q is heat change of the solution 2. use mass of solution, specific heat capacity and temperature change 3. divide by moles of limiting reagent 4. convert J to kJ mol⁻¹ and use the correct sign	9701_s23_qp_23 Q3(b)(ii); 9701_s23_qp_21 Q2(b)(ii); 9701_s20_qp_22 Q3(d)(ii); +1 additional hits
9% 4/44	water of crystallisation	x = n(H₂O) / n(anhydrous salt)	1. n(H₂O) = mass lost / 18.0 2. n(anhydrous salt) = mass of residue / Mr 3. simplify the ratio to find x	9701_s23_qp_21 Q2(b)(ii); 9701_s20_qp_23 Q2(d)(ii); 9701_s20_qp_21 Q2(b); +1 additional hits
2% 1/44	M+2 halogen pattern	one Cl: M : M+2 ≈ 3 : 1 one Br: M : M+2 ≈ 1 : 1	1. M+2 comes from ³⁷Cl instead of ³⁵Cl, or ⁸¹Br instead of ⁷⁹Br 2. use the ratio to identify Cl/Br in the molecule	9701_s22_qp_23 Q5(b)(ii)

MS Equation Bank: Template / Fixed Equations Only

筛查口径：2020-2025 AS Paper 2 MS，N = 44。这里不再收录普通一次性反应；只保留可套用模板、CIE 常反复要求的固定方程式，或答案几乎唯一的方程式。计算公式仍放在上面的 Formula / Expression Table。
MS 通用规则：multiples / fractions of coefficients are acceptable unless stated otherwise；state symbols are ignored unless the question or MS specifically asks for them.

Area	Type	Equations to know	When to write	Sources
ionisation	template	X(g) → X⁺(g) + e⁻ Xⁿ⁺(g) → X⁽ⁿ⁺¹⁾⁺(g) + e⁻	1. include gaseous state symbols for atom/ion 2. show one electron removed 3. use the correct charge for the numbered IE	9701_s25_qp_24 Q1(c)(i); 9701_m22_qp_22 Q1(a); 9701_w20_qp_21 Q1(a); +8 additional hits
formation equation	template	elements in standard states → 1 mol compound Example: H₂(g) + ½O₂(g) → H₂O(l)	1. product coefficient must be 1 2. reactants are elements in their standard states 3. include state symbols when the question/MS asks	9701_s24_qp_23 Q3(a); 9701_s24_qp_21 Q4(b)(i)
amphoteric oxide	template / fixed	Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄ or Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O	1. use these to show amphoteric behaviour with acid and alkali 2. tetrahydroxoaluminate and aluminate forms have both appeared as accepted balanced answers	9701_w25_qp_21 Q2(c)(ii); 9701_s25_qp_24 Q1(d)(ii); 9701_s24_qp_23 Q1(c)(ii); 9701_m22_qp_22 Q2(b)(ii); 9701_w20_qp_22 Q2(e)(i-ii)
Period 3 oxide / chloride hydrolysis	fixed	P₄O₁₀ + 6H₂O → 4H₃PO₄ P₄O₁₀ + 12NaOH → 4Na₃PO₄ + 6H₂O PCl₅ + 4H₂O → H₃PO₄ + 5HCl POCl₃ + 3H₂O → H₃PO₄ + 3HCl SiCl₄ + 2H₂O → SiO₂ + 4HCl	1. chloride hydrolysis answers need acidic products 2. SiCl₄ gives SiO₂ + HCl in recent MS wording 3. P₄O₁₀ with excess NaOH gives phosphate salt	9701_w25_qp_24 Q2(c)(iii); 9701_s25_qp_22 Q1(b)(i); 9701_s24_qp_23 Q1(c)(ii); 9701_w23_qp_21 Q1(d)(ii); 9701_m22_qp_22 Q2(c)(iv), Q3(b)(i); 9701_w21_qp_21 Q3(b)(ii)
chlorine disproportionation / water	fixed	Cl₂ + H₂O ⇌ HCl + HOCl Cl₂ + 2NaOH → NaCl + NaClO + H₂O 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O	1. cold dilute alkali gives NaClO 2. hot concentrated alkali gives NaClO₃ 3. HOCl/ClO⁻ is the active species in water purification	9701_m25_qp_22 Q3(b); 9701_m24_qp_22 Q2(b)(iii); 9701_s23_qp_22 Q2(d); 9701_s21_qp_23 Q1(c); 9701_m21_qp_22 Q2(d)(ii)
halide redox	template / fixed	displacement: X₂ + 2Y⁻ → 2X⁻ + Y₂ H₂SO₄ acid-base: NaX + H₂SO₄ → NaHSO₄ + HX bromide redox: 2Br⁻ + 2H⁺ + H₂SO₄ → Br₂ + 2H₂O + SO₂ iodide redox: 8HI + H₂SO₄ → 4I₂ + H₂S + 4H₂O	1. choose X₂/Y⁻ from halogen reactivity 2. with concentrated H₂SO₄, Br⁻/I⁻ can reduce sulfuric acid 3. use oxidation numbers to justify redox	9701_s24_qp_21 Q1(c-d); 9701_s22_qp_22 Q3(d)(ii); 9701_s21_qp_21 Q3(a)(i), Q3(d)
NOₓ / SOₓ pollution	fixed	N₂ + O₂ → 2NO NO + ½O₂ → NO₂ 3NO₂ + H₂O → 2HNO₃ + NO NO₂ + SO₂ → NO + SO₃ 2NO + O₂ → 2NO₂ SO₃ + H₂O → H₂SO₄	1. the two NO₂/SO₂ equations show NO₂ as a catalyst and regenerated 2. SO₃ + water can be written when MS allows equation form for sulfuric acid formation 3. NO forms from N₂/O₂ at high temperature	9701_s24_qp_23 Q2(d)(i); 9701_m24_qp_22 Q3(b)(i); 9701_s23_qp_21 Q5(b)(i-ii); 9701_m22_qp_22 Q2(d)(i); 9701_s20_qp_21 Q3(e)(ii)
ammonia / ammonium	template	NH₃ + H₂O ⇌ NH₄⁺ + OH⁻ NH₄⁺ + OH⁻ → NH₃ + H₂O	1. reversible equation shows weak base behaviour 2. ionic equation is used for ammonium salt + alkali test	9701_s24_qp_23 Q4(b)(ii); 9701_w22_qp_22 Q1(c)(ii); 9701_s22_qp_21 Q2(d)(ii)
organic combustion	template	CₓHᵧOᶻ + O₂ → xCO₂ + y/2H₂O	1. complete combustion gives CO₂ and H₂O 2. fractional O₂ coefficients are acceptable unless whole numbers are required	9701_w25_qp_24 Q3(b)(iv); 9701_w25_qp_22 Q3(e)(iii); 9701_s23_qp_21 Q5(a)(i); 9701_s20_qp_23 Q3(c)(ii)
free-radical substitution	template	initiation: Cl₂ / Br₂ → 2Cl· / 2Br· propagation 1: RH + Cl· → R· + HCl propagation 2: R· + Cl₂ → RCl + Cl· termination: R· + Cl· → RCl or R· + R· → R-R	1. radical dot must be on the radical species 2. initiation needs homolytic fission/UV context if asked 3. propagation regenerates a halogen radical	9701_w25_qp_23 Q3(c)(ii); 9701_w25_qp_22 Q4(a)(ii); 9701_w24_qp_21 Q2(b)(iii); 9701_s23_qp_21 Q3(d)(ii); 9701_s20_qp_23 Q4(b)(ii-iv)
halogenoalkane substitution / elimination	template	substitution: RCl + NaOH(aq) → ROH + NaCl elimination: RCl + NaOH(ethanol) → alkene + NaCl + H₂O	1. aqueous hydroxide gives alcohol 2. ethanolic hydroxide with heat/reflux gives alkene 3. adapt the carbon skeleton from the question	9701_w25_qp_23 Q4(a)(ii); 9701_w25_qp_21 Q4(a)(ii); 9701_s20_qp_22 Q4(c)(ii)
oxidation / reduction	template	oxidation: RCH₂OH + 2[O] → RCO₂H + H₂O; R₂CHOH + [O] → R₂CO + H₂O reduction: RCHO + 2[H] → RCH₂OH; R₂CO + 2[H] → R₂CHOH; RCO₂H + 4[H] → RCH₂OH + H₂O	1. primary alcohol to acid needs 2[O] 2. secondary alcohol to ketone needs [O] 3. carboxylic acid reduction needs 4[H] and forms water	9701_w25_qp_22 Q4(c)(ii); 9701_s25_qp_22 Q4(a)(ii); 9701_w24_qp_21 Q4(c)(i); 9701_w21_qp_21 Q4(a)(ii); 9701_m21_qp_22 Q4(d)(i); 9701_s20_qp_21 Q6(f)(i)
nitrile hydrolysis / reduction	template	acid hydrolysis: RCN + 2H₂O + H⁺ → RCOOH + NH₄⁺ alkaline hydrolysis: RCN + NaOH + H₂O → RCO₂Na + NH₃ reduction: RCN + 2H₂ → RCH₂NH₂	1. acid hydrolysis gives carboxylic acid + ammonium 2. alkaline hydrolysis gives carboxylate salt + ammonia 3. the nitrile carbon becomes the carboxyl/amine carbon	9701_w25_qp_24 Q4(b)(ii); 9701_s25_qp_24 Q4(d)(i); 9701_s25_qp_22 Q4(b)(iii); 9701_m24_qp_22 Q4(b)(iii); 9701_s21_qp_22 Q5(b)(iv); 9701_w20_qp_21 Q3(c)(iv)
esterification / acid reactions	template	esterification: RCOOH + R′OH → RCOOR′ + H₂O neutralisation: RCOOH + NaOH → RCOONa + H₂O carbonate: RCOOH + carbonate → carboxylate salt + CO₂ + H₂O	1. ester formula must connect acyl O correctly 2. carbonate reaction is useful as a carboxylic acid test template 3. adapt salt stoichiometry to mono-/di-carboxylic acids	9701_s25_qp_24 Q4(c)(ii); 9701_s25_qp_21 Q5(c)(i); 9701_s23_qp_22 Q3(a)(iv)
iodoform / haloform	fixed	CH₃COCH₃ + 3I₂ + 4OH⁻ → CH₃COO⁻ + 3H₂O + 3I⁻ + CHI₃ CH₃COCH₃ + 3NaClO → CHCl₃ + CH₃COONa + 2NaOH	1. CHI₃ / CHCl₃ product is often a named-product mark 2. balancing may be a separate mark 3. use for methyl ketone / suitable secondary alcohol context	9701_w24_qp_23 Q2(c)(iii); 9701_w24_qp_21 Q2(c)(iii); 9701_w20_qp_23 Q4(c)(vi); 9701_w20_qp_21 Q4(c)(vi)

High-Frequency Colour / State / Precipitate Observations

频率口径：只统计 2020-2025 AS Paper 2 MS 中明确作为 observation / appearance / state / precipitate 给分的答案片段；同一份卷子同一现象只计 1 次。

Frequency	Papers	Chapter	Observation / substance	MS-ready wording	Sources
30%	13/44	14 / 17	Br₂(aq) / bromine water	1. alkene / C=C: orange/brown/red bromine water turns colourless / decolourises 2. no C=C: no visible change / solution stays orange-brown	9701_s21_qp_23 Q1(b); 9701_s21_qp_21 Q5(c)(ii); 9701_w20_qp_22 Q4(c); +11 additional hits
30%	13/44	17	2,4-DNPH	1. aldehydes and ketones give a red/orange/yellow precipitate / solid / crystals 2. no carbonyl compound: no precipitate / no visible change	9701_s21_qp_23 Q4(b); 9701_w20_qp_22 Q4(c); 9701_s20_qp_21 Q6(d); +10 additional hits
20%	9/44	11	halogen colours and states	1. chlorine: green / yellow-green gas 2. bromine: orange/brown/red-brown liquid 3. iodine: dark grey/black solid; iodine vapour is purple	9701_w24_qp_23 Q2(a)(i); 9701_w24_qp_21 Q2(a)(i); 9701_s21_qp_23 Q1(a)(ii); +8 additional hits
18%	8/44	14 / 18	carbonate / hydrogencarbonate with acid	1. effervescence / fizzing / bubbling is seen 2. gas is CO₂; if tested, CO₂ turns limewater milky 3. no carboxylic acid/acidic group: no visible change	9701_s22_qp_21 Q4(b)(i); 9701_s21_qp_23 Q4(b); 9701_w20_qp_22 Q4(c); +5 additional hits
16%	7/44	16 / 17	alkaline I₂ / iodoform test	1. yellow precipitate forms 2. precipitate is CHI₃ / iodoform / triiodomethane 3. positive for CH₃CO- or CH₃CH(OH)- groups	9701_w22_qp_23 Q4(a); 9701_w22_qp_22 Q3(a)(i); 9701_w22_qp_21 Q4(a); +4 additional hits
16%	7/44	17	Tollens’ / Fehling’s observations	1. Tollens’ reagent: aldehyde gives silver mirror or silver/grey/black precipitate 2. Fehling’s solution: aldehyde gives brick-red precipitate 3. ketone: no reaction / no visible change	9701_m22_qp_22 Q4(a)(i); 9701_m21_qp_22 Q4(b); 9701_w20_qp_22 Q4(a)(iv); +4 additional hits
16%	7/44	11 / 15	AgNO₃ halide precipitates	1. Cl⁻ gives white AgCl precipitate 2. Br⁻ gives cream/off-white AgBr precipitate 3. I⁻ gives yellow AgI precipitate	9701_w23_qp_23 Q1(c); 9701_w23_qp_21 Q1(c); 9701_s22_qp_22 Q2(d); +4 additional hits
14%	6/44	11 / 15	AgX precipitate solubility in NH₃	1. AgCl dissolves in dilute/excess NH₃ 2. AgBr is partly/slightly soluble in concentrated NH₃ 3. AgI is insoluble; solid remains	9701_s22_qp_22 Q2(d); 9701_s20_qp_22 Q4(a)(iii); 9701_m20_qp_22 Q2(c)(i); +3 additional hits
14%	6/44	16 / 18	sodium metal test	1. Na(s) disappears/dissolves and effervescence / fizzing / bubbles are seen 2. gas is H₂ 3. positive with alcohols or carboxylic acids; sodium oxide gives no effervescence	9701_s23_qp_23 Q5(d); 9701_w22_qp_23 Q4(a); 9701_w22_qp_21 Q4(a); +3 additional hits
9%	4/44	16 / 17	acidified K₂Cr₂O₇ / KMnO₄ colour change	1. acidified K₂Cr₂O₇ changes from orange to green; Cr³⁺ is green 2. acidified KMnO₄ / MnO₄⁻ changes from purple to colourless 3. no oxidation: no visible change	9701_w22_qp_23 Q4(a); 9701_w22_qp_22 Q3(a)(i); 9701_w22_qp_21 Q4(a); +1 additional hits
7%	3/44	11	concentrated H₂SO₄ with halides	1. Cl⁻: steamy/misty fumes of HCl; acid-base only 2. Br⁻: brown/red-brown Br₂ forms; H₂SO₄ is reduced 3. I⁻: black solid / purple vapour I₂, yellow sulfur, rotten-egg H₂S and/or effervescence may be seen	9701_w25_qp_24 Q1(c)(i); 9701_w23_qp_23 Q1(c); 9701_w23_qp_21 Q1(c)
7%	3/44	9 / 10	sulfate / hydroxide precipitates	1. BaSO₄ is an insoluble white precipitate/solid 2. Mg(OH)₂ is insoluble / forms a white precipitate; Ba(OH)₂ is soluble enough to distinguish 3. use a soluble sulfate or hydroxide reagent when asked	9701_s23_qp_21 Q2(c)(ii); 9701_m23_qp_22 Q2(c); 9701_s22_qp_21 Q1(c)
7%	3/44	9	Period 3 chloride states / water observations	1. SiCl₄ is a colourless liquid; with water it gives misty fumes and white solid/suspension/precipitate of SiO₂ 2. PCl₅ is a white/pale yellow solid; with water it gives misty/steamy fumes and an acidic colourless solution 3. MgCl₂/PCl₅ may be white crystals/solid; SiCl₄ is the key liquid exception	9701_s25_qp_22 Q1(b)(ii); 9701_s23_qp_21 Q3(b); 9701_s21_qp_23 Q3(a)(i); +1 additional hits
0%	0/44	12	nitrogen oxides appearance	1. NO is a colourless gas 2. NO₂ is a brown gas 3. this is syllabus/textbook background; no recent P2 MS observation hit in the current 44-paper set	no 2020-2025 P2 MS hit

Organic Mechanism MS Screenshots

机理题按文字采分点背；截图只用来核对 curly arrow 起点、终点、中间体和电荷位置。

Frequency	Papers	Chapter	Mechanism	Sources
64%	28/44	14-17	electrophilic addition to C=C / curly-arrow rule 1. curly arrow starts at the C=C π bond 2. show induced dipole in Br₂ / H-X and bond-breaking arrow to the leaving atom 3. draw the carbocation / cyclic intermediate as required 4. nucleophile arrow starts from lone pair/negative charge	9701_s25_qp_23 Q6(b); 9701_s25_qp_22 Q3(a)(ii); 9701_w24_qp_22 Q4(a); +25 additional hits
18%	8/44	14	free-radical substitution 1. initiation: homolytic fission in UV light forms halogen radicals 2. propagation 1: a halogen radical removes H from an alkane to form an alkyl radical and HCl/HBr 3. propagation 2: the alkyl radical reacts with Cl2/Br2 to form a halogenoalkane and regenerate a halogen radical 4. termination: two radicals combine to form a stable molecule	9701_w24_qp_21 Q2(b)(iii); 9701_m21_qp_22 Q2(g)(i); 9701_s20_qp_23 Q4(b)(ii); +22 additional hits
9%	4/44	15	nucleophilic substitution of tertiary/secondary halogenoalkane (SN1-style shown) 1. show Cδ+–Xδ− dipole 2. curly arrow from C-X bond to X when bond breaks 3. draw the carbocation / intermediate where required 4. curly arrow from nucleophile lone pair to C+ / electron-deficient carbon	9701_s24_qp_22 Q4(b); 9701_s21_qp_22 Q3(c)(i); 9701_w20_qp_21 Q4(c)(ii); +2 additional hits
2%	1/44	15 / 19	SN2 nucleophilic substitution / CN⁻ chain extension 1. show Cδ+–Brδ− dipole 2. curly arrow from C–Br bond to Br / Brδ− as bond breaks 3. curly arrow starts from lone pair on C of CN⁻ 4. arrow goes to C-1 / δ⁺ carbon of the bromoalkane; no carbocation intermediate is drawn	9701_s22_qp_22 Q5(c)(i)
9%	4/44	17 / 19	HCN nucleophilic addition to carbonyl 1. curly arrow from lone pair on CN⁻ to δ⁺ carbonyl carbon 2. show C=O dipole and arrow from C=O π bond to O 3. protonation arrow from O⁻/alkoxide to H of HCN/H⁺; regenerate CN⁻ if shown	9701_s23_qp_23 Q6(b)(ii); 9701_w20_qp_21 Q3(c)(iii); 9701_s20_qp_22 Q5(b)(i); +8 additional hits

Cross-Chapter MS Answering Rules

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
64%	28/44	28	mechanism curly-arrow rule	1. curly arrows start at a lone pair/electron pair/bond/negative charge 2. arrow points to the atom or bond receiving the electron pair 3. for bond breaking, arrow goes from the bond to the atom receiving the electrons	9701_w25_qp_24 Q3(b)(ii); 9701_s25_qp_22 Q3(a)(ii); 9701_m25_qp_22 Q4(b)(i); +25 additional hits
36%	16/44	19	equations / state symbols	1. use correct formulae 2. balance the equation 3. include charges where needed 4. include state symbols when the question asks for them	9701_s20_qp_22 Q1(e)(ii); 9701_s20_qp_21 Q2(a)(i); 9701_s20_qp_21 Q1(c)(i); +20 additional hits
34%	15/44	15	organic conditions	1. acidified K₂Cr₂O₇/KMnO₄ plus distil/reflux 2. KCN/NaOH in ethanol plus heat/reflux 3. NH₃ in ethanol heated under pressure 4. conditions are often separate marks	9701_s20_qp_22 Q4(a)(iii); 9701_m20_qp_22 Q3(a)(i); 9701_m20_qp_22 Q2(c)(i); +38 additional hits

1 Atomic Structure / Electrons In Atoms

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
36%	16/44	18	IE trend explanation	1. compare nuclear charge/proton number 2. compare shielding and distance from the nucleus 3. link these to nuclear attraction for the outer electron	9701_w20_qp_22 Q1(b)(iv); 9701_w20_qp_21 Q1(c); 9701_w20_qp_21 Q1(b); +24 additional hits
9%	4/44	4	same chemical properties of isotopes	1. same electronic configuration 2. same number and arrangement of outer-shell electrons	9701_s25_qp_21 Q2(e); 9701_s22_qp_23 Q1(d)
7%	3/44	3	free radical definition	1. species with one or more unpaired electrons	9701_w24_qp_23 Q2(b)(i); 9701_w24_qp_21 Q2(b)(i); 9701_w23_qp_22 Q2(e)(i)
7%	3/44	3	isotopes definition	1. same number of protons 2. different number of neutrons	9701_s22_qp_21 Q1(e)(iii); 9701_s22_qp_21 Q1(e)(ii); 9701_s20_qp_21 Q1(a)(ii); +7 additional hits
2%	1/44	1	successive ionisation equation	1. write Xⁿ⁺(g) → X⁽ⁿ⁺¹⁾⁺(g) + e⁻ 2. one electron is removed from a gaseous ion 3. state symbols are needed	9701_s25_qp_24 Q1(c)(i); 9701_m23_qp_22 Q2(a)(i)

2 Atoms, Molecules And Stoichiometry

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
20%	9/44	9	relative atomic/isotopic/molecular mass	1. mass / weighted average mass of atom, isotope or molecule 2. compared with 1/12 of the mass of a carbon-12 atom or the unified atomic mass unit	9701_w22_qp_21 Q1(a)(ii); 9701_s20_qp_23 Q2(a); 9701_s20_qp_22 Q1(a); +6 additional hits
9%	4/44	4	empirical formula definition	1. simplest/lowest whole-number ratio of atoms of each element in a compound	9701_s22_qp_21 Q4(a); 9701_s21_qp_23 Q3(c); 9701_s20_qp_23 Q3(b)(iii); +1 additional hits
9%	4/44	4	hydrated salt / water of crystallisation calculation	1. calculate mol anhydrous salt 2. calculate mol H₂O separately 3. find the simplest H₂O : salt ratio	9701_s23_qp_21 Q2(b)(ii); 9701_s20_qp_23 Q2(d)(ii); 9701_s20_qp_21 Q2(b); +1 additional hits
7%	3/44	3	mole / Avogadro constant	1. one mole contains Avogadro constant / 6.02 × 10²³ specified particles	9701_s25_qp_23 Q4(a)(iv); 9701_s22_qp_23 Q1(f)(i); 9701_s21_qp_21 Q1(a)(iii)

3 Chemical Bonding

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
59%	26/44	23	bonding diagrams: metallic / dot-and-cross / coordinate	1. for dot-and-cross diagrams, show outer-shell electrons only and use different symbols for electrons from different atoms 2. covalent bonds are shared pairs; coordinate/dative bonds have both electrons in the shared pair donated by one atom/species 3. metallic bonding diagrams need a lattice/regular arrangement of positive ions/cations and delocalised electrons 4. for NH₄Cl, show ionic attraction between NH₄⁺ and Cl⁻, four N-H covalent bonds in NH₄⁺, and one N→H coordinate bond / one N-H bonding pair from N	9701_s24_qp_23 Q4(a); 9701_w20_qp_21 Q3(a)(i); 9701_s20_qp_22 Q1(b); +23 additional hits
50%	22/44	27	simple molecular boiling/melting	1. greater number of electrons in the molecules 2. stronger instantaneous dipole-induced dipole forces / van der Waals’ forces between molecules 3. more energy is needed to overcome the intermolecular forces	9701_w20_qp_23 Q4(a)(iii); 9701_w20_qp_21 Q4(a)(iii); 9701_s20_qp_21 Q1(b)(i); +21 additional hits
43%	19/44	14	σ and π bonds / orbital overlap / hybridisation	1. a σ bond is formed by direct/head-on/end-on overlap of orbitals between the bonding atoms 2. a π bond is formed by sideways/lateral overlap of adjacent p orbitals 3. single bond = 1σ; double bond = 1σ + 1π; triple bond = 1σ + 2π 4. common hybridisation: sp gives linear/triple-bond centres; sp² gives trigonal planar/C=C centres; sp³ gives tetrahedral/saturated carbon or ammonium centres	9701_s24_qp_23 Q1(a)(ii); 9701_s24_qp_21 Q4(b)(i-ii); 9701_s22_qp_21 Q2(a); +16 additional hits
32%	14/44	14	metallic bonding / conductivity	1. giant metallic lattice / regular arrangement of positive ions/cations surrounded by delocalised electrons 2. many strong electrostatic attractions between cations and delocalised electrons / strong metallic bonds need more energy to overcome, so melting point is high 3. delocalised electrons are free to move through the structure and carry charge	9701_w24_qp_21 Q3(a)(iii); 9701_s22_qp_23 Q1(f)(ii); 9701_s22_qp_22 Q1(a); +5 additional hits
16%	7/44	7	coordinate/dative bond definition	1. a covalent bond/shared pair is formed 2. both electrons in the shared pair are donated by one atom/species	9701_s21_qp_21 Q2(a)(i); 9701_m21_qp_22 Q2(e)(i); 9701_s20_qp_21 Q1(b)(ii); +4 additional hits
14%	6/44	6	hydrogen bonding	1. H atom is bonded to highly electronegative N/O/F in one molecule 2. H atom is attracted to a lone pair on N/O/F in another molecule 3. hydrogen bonds are stronger than other intermolecular forces, so more energy is needed to overcome them	9701_w21_qp_22 Q1(a)(ii); 9701_w21_qp_21 Q4(d); 9701_s21_qp_23 Q2(b)(iii); +3 additional hits
9%	4/44	4	covalent bond definition	1. electrostatic attraction 2. between the nuclei of two atoms and a shared pair of electrons	9701_w21_qp_22 Q2(d)(iii); 9701_s21_qp_22 Q2(b)(i); 9701_s21_qp_21 Q2(a)(i); +13 additional hits
5%	2/44	2	electronegativity definition	1. power of an atom to attract electrons to itself	9701_w24_qp_22 Q2(c)(ii); 9701_s24_qp_23 Q4(c)(ii); 9701_m22_qp_22 Q3(a); +1 additional hits
5%	2/44	2	ionic lattice melting point	1. many strong electrostatic attractions between oppositely charged ions 2. more energy is needed to overcome them	9701_s22_qp_23 Q2(b)(ii); 9701_w20_qp_23 Q3(a)(iv); 9701_w20_qp_21 Q3(a)(iv); +2 additional hits
9%	4/44	4	VSEPR shape / bond angle	1. electron pairs repel 2. lone pairs repel more than bond pairs 3. give the correct shape and bond angle	9701_w20_qp_22 Q2(f); 9701_s20_qp_22 Q1(d); 9701_s20_qp_21 Q4(c); +12 additional hits

4 States Of Matter

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
18%	8/44	8	ideal gas equation calculation	1. use pV = nRT with Pa, m³ and K	9701_m21_qp_22 Q1(b)(ii); 9701_m21_qp_22 Q1(b)(i); 9701_w20_qp_22 Q3(d)(iii); +3 additional hits
5%	2/44	2	temperature and kinetic energy	1. higher temperature means greater average kinetic energy	9701_m21_qp_22 Q1(b)(iii)
2%	1/44	1	gas pressure explanation	1. pressure is force per unit area from collisions of gas molecules with the container walls	9701_s21_qp_23 Q2(b)(i); 9701_m21_qp_22 Q3(d)(iv); 9701_m21_qp_22 Q1(b)(iii)

5 Chemical Energetics

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
18%	8/44	8	enthalpy change of formation	1. enthalpy/energy change when one mole of compound/substance is formed 2. from its elements in their standard states	9701_w21_qp_22 Q1(b); 9701_s20_qp_21 Q3(a); 9701_m20_qp_22 Q1(g)(ii); +6 additional hits
11%	5/44	5	bond energy calculation	1. ΔH = sum of bond energies broken - sum of bond energies formed	9701_s22_qp_23 Q3(a)(ii); 9701_w21_qp_22 Q1(c)(iii); 9701_m21_qp_22 Q2(c)(i); +3 additional hits
9%	4/44	4	enthalpy change of combustion	1. enthalpy/energy change when one mole of substance/compound burns completely in excess O₂	9701_w21_qp_21 Q1(b)(i); 9701_s20_qp_23 Q3(c)(i); 9701_s20_qp_22 Q3(d)(i); +1 additional hits
9%	4/44	4	q = mcΔT / calorimetry	1. q = mcΔT for the solution 2. ΔH = -q / moles of limiting reagent 3. convert J to kJ mol⁻¹ 4. include the correct sign	9701_s23_qp_23 Q3(b)(ii); 9701_s23_qp_21 Q2(b)(ii); 9701_s20_qp_22 Q3(d)(ii); +1 additional hits

6 Electrochemistry: Redox

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
32%	14/44	15	reducing agent	1. donates electrons and is oxidised	9701_w20_qp_22 Q4(b)(iii); 9701_w20_qp_21 Q3(c)(ii); 9701_m20_qp_22 Q2(c)(ii); +14 additional hits
25%	11/44	13	oxidising agent	1. accepts electrons and is reduced	9701_m21_qp_22 Q4(c)(i); 9701_m20_qp_22 Q2(c)(ii); 9701_m20_qp_22 Q2(b)(i); +11 additional hits
14%	6/44	6	disproportionation definition	1. same species is both oxidised and reduced	9701_s21_qp_21 Q1(b)(ii); 9701_m21_qp_22 Q2(d)(i); 9701_s20_qp_22 Q2(c)(ii); +5 additional hits
11%	5/44	5	redox by oxidation numbers	1. one species increases oxidation number while another decreases	9701_w21_qp_22 Q1(d)(ii); 9701_w21_qp_21 Q1(c)(iii); 9701_s21_qp_21 Q4(a); +2 additional hits
2%	1/44	1	electron transfer explanation	1. oxidation is electron loss 2. reduction is electron gain	9701_m24_qp_22 Q1(d)(i)

7 Equilibria

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
25%	11/44	11	Bronsted acid / strong vs weak acid	1. acid = proton/H⁺ donor 2. strong acid fully dissociates/fully ionises in aqueous solution/water 3. weak acid partially dissociates/partially ionises in aqueous solution/water	9701_w20_qp_23 Q2(b)(i); 9701_w20_qp_22 Q3(d)(ii); 9701_w20_qp_21 Q2(b)(i); +11 additional hits
14%	6/44	6	Kp expression / units	1. Kp = product partial pressures over reactant partial pressures 2. each partial pressure is raised to its stoichiometric coefficient 3. omit solids from the expression 4. derive units from the expression	9701_w21_qp_22 Q1(c)(i-ii); 9701_s21_qp_23 Q2(c)(iii); 9701_m20_qp_22 Q1(f)(ii); +3 additional hits
14%	6/44	6	Kc expression / units	1. Kc = product concentrations over reactant concentrations in square brackets 2. each concentration is raised to its stoichiometric coefficient 3. derive units from the expression 4. pressure/catalyst changes do not change Kc; temperature changes can change Kc	9701_s24_qp_21 Q3(c)(ii); 9701_s23_qp_23 Q4(b)(ii); 9701_s22_qp_23 Q3(a)(iii); +3 additional hits
11%	5/44	5	dynamic equilibrium definition	1. system is closed 2. rate of forward reaction equals rate of reverse/backward reaction 3. concentrations or macroscopic properties remain constant	9701_w25_qp_21 Q1(d)(i); 9701_s25_qp_21 Q3(b); 9701_s22_qp_22 Q3(a)(i); +2 additional hits
9%	4/44	4	closed system condition	1. closed/sealed system or container 2. no substances enter or leave	9701_w25_qp_22 Q2(e)(ii); 9701_w25_qp_21 Q1(d)(ii); 9701_m20_qp_22 Q1(f)(i); +1 additional hits
5%	2/44	2	Le Chatelier principle	1. if a condition changes, the equilibrium shifts/moves to minimise the change	9701_w25_qp_21 Q1(d)(iii); 9701_s25_qp_21 Q3(b); 9701_s24_qp_21 Q3(a); +1 additional hits
2%	1/44	1	catalyst and equilibrium	1. catalyst gives no change in equilibrium position 2. it reduces the time taken to reach the same equilibrium	9701_s22_qp_23 Q3(a)(iv)

8 Reaction Kinetics

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
20%	9/44	10	frequency of effective collisions	1. rate increases/decreases with the frequency of successful/effective collisions per unit time	9701_s22_qp_21 Q1(g); 9701_m22_qp_22 Q2(b)(iii); 9701_m21_qp_22 Q1(c)(ii); +7 additional hits
18%	8/44	8	temperature effect	1. higher temperature means particles have greater average kinetic energy, so a greater proportion of particles have E ≥ Ea 2. frequency of successful/effective collisions increases	9701_s25_qp_21 Q3(a)(ii); 9701_s24_qp_23 Q2(b)(ii)
11%	5/44	5	catalyst lowers Ea	1. catalyst provides an alternative route with lower activation energy 2. a greater proportion of particles have E ≥ Ea 3. successful collisions are more frequent	9701_m21_qp_22 Q1(a)(ii); 9701_s20_qp_21 Q3(e)(i); 9701_m20_qp_22 Q1(b); +7 additional hits
2%	1/44	1	activation energy definition	1. minimum energy particles must have for a successful/effective collision	9701_s20_qp_21 Q3(e)(i); 9701_s20_qp_21 Q3(c); 9701_m20_qp_22 Q1(c); +14 additional hits
2%	1/44	1	concentration/pressure effect	1. more particles per unit volume 2. higher frequency of successful/effective collisions	9701_s25_qp_23 Q4(a)(iii)

9 Periodicity: Period 3

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
32%	14/44	18	Period 3 melting point structure	1. identify the structure: simple molecular / giant metallic / giant covalent as appropriate 2. simple molecular substances: only weak intermolecular / van der Waals’ forces are overcome, so less energy is needed 3. giant metallic/covalent substances: many strong metallic/covalent bonds or attractions must be overcome/broken, so more energy is needed	9701_w21_qp_23 Q3(a)(i); 9701_w21_qp_21 Q3(a)(i); 9701_w20_qp_22 Q2(f); +12 additional hits
20%	9/44	10	Period 3 chloride hydrolysis	1. SiCl₄ + 2H₂O → SiO₂ + 4HCl 2. PCl₅ + 4H₂O → H₃PO₄ + 5HCl 3. include state symbols / acidic products if the question asks	9701_w21_qp_23 Q3(b)(ii); 9701_w21_qp_21 Q3(b)(ii); 9701_w20_qp_22 Q3(b)(ii); +12 additional hits
14%	6/44	6	Period 3 atomic radius	1. nuclear charge/proton number increases across the period 2. shielding is similar 3. attraction for outer electrons increases, so atomic radius decreases	9701_w20_qp_22 Q1(b)(iv)
14%	6/44	6	Period 3 conductivity	1. conductivity requires mobile charged particles 2. Na, Mg and Al conduct because delocalised electrons are free to move through the giant metallic structure 3. Si / simple molecular substances do not conduct because there are no mobile charged particles / no delocalised electrons	9701_w25_qp_22 Q2(a)(ii); 9701_s25_qp_24 Q1(b)
7%	3/44	3	amphoteric oxides/hydroxides	1. Al₂O₃/Al(OH)₃ are amphoteric: they react with both acids and bases to form salts	9701_s20_qp_21 Q1(c)(ii); 9701_m20_qp_22 Q1(e)(i)
2%	1/44	1	acidic/basic oxides	1. metal oxides are basic 2. non-metal oxides are acidic 3. Al₂O₃/Al(OH)₃ are amphoteric. Give acid/base equations if asked	9701_s21_qp_23 Q3(a)(i)

10 Group 2

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
9%	4/44	4	Group 2 thermal stability	1. down Group 2 the cation radius increases and charge density decreases 2. the cation polarises the carbonate/nitrate ion less 3. decomposition is less easy and thermal stability increases	9701_w21_qp_23 Q2(a)(iii); 9701_w21_qp_21 Q2(a)(iii); 9701_m21_qp_22 Q2(c)(i); +8 additional hits
7%	3/44	3	basic oxides/hydroxides reaction	1. Group 2 oxides/hydroxides neutralise acids to form salt and water 2. soluble oxides also form hydroxides with water	9701_w20_qp_22 Q2(c)
7%	3/44	3	hydroxide solubility trend	1. Group 2 hydroxides become more soluble down the group	9701_m23_qp_22 Q2(c); 9701_s22_qp_22 Q2(c)(iv)
2%	1/44	1	sulfate solubility trend	1. Group 2 sulfates become less soluble down the group 2. BaSO4 is insoluble	9701_s23_qp_21 Q2(c)(ii); 9701_s23_qp_21 Q2(c)(i); 9701_m23_qp_22 Q2(c)

11 Group 17

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
30%	13/44	11	chlorine disproportionation / water purification	1. cold dilute NaOH: Cl₂ + 2NaOH → NaCl + NaClO + H₂O 2. hot concentrated NaOH: 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O 3. in water: Cl₂ + H₂O ⇌ HCl + HOCl 4. HOCl / ClO⁻ kills bacteria/microbes; this is the active species in water purification 5. chlorine disproportionates because Cl is both oxidised and reduced	9701_m25_qp_22 Q3(b); 9701_s23_qp_22 Q2(d); 9701_s21_qp_23 Q1(c); +10 additional hits
14%	6/44	6	AgNO₃ / NH₃ test	1. acidify with dilute HNO₃, then add aqueous AgNO₃ 2. Cl⁻ gives a white precipitate, soluble in dilute NH₃ 3. Br⁻ gives a cream/off-white precipitate, partly/slightly soluble in concentrated NH₃ 4. I⁻ gives a yellow precipitate, insoluble in concentrated NH₃	9701_w22_qp_21 Q2(c); 9701_s22_qp_22 Q2(d); 9701_m20_qp_22 Q2(c)(i); +6 additional hits
11%	5/44	5	halogen volatility	1. more electrons down the group 2. stronger instantaneous dipole-induced dipole forces / van der Waals’ forces between molecules 3. more energy is required to overcome these forces 4. boiling point increases / volatility decreases	9701_w21_qp_21 Q1(a)(iv); 9701_w20_qp_23 Q4(a)(i); 9701_w20_qp_21 Q4(a)(i); +3 additional hits
9%	4/44	4	halide reducing power	1. reducing power increases down the group 2. halide ion is oxidised / loses an electron more readily 3. outer electron is less strongly attracted because distance/shielding increases	9701_s22_qp_22 Q3(d)(iii); 9701_m21_qp_22 Q2(c)(iii)
7%	3/44	3	conc H₂SO₄ with halides	1. with Cl⁻, H₂SO₄ acts as an acid only 2. with Br⁻/I⁻, H₂SO₄ is reduced and acts as an oxidising agent 3. Br₂/I₂ and sulfur-containing reduction products can form	9701_m22_qp_22 Q3(b)(ii); 9701_s21_qp_21 Q3(d); 9701_s21_qp_21 Q3(a)(i); 9701_m20_qp_22 Q2(c)(ii)
5%	2/44	2	halogen oxidising power	1. oxidising power decreases down the group 2. halogen atom gains an electron less readily 3. distance/shielding increases, so attraction for the incoming electron is weaker	9701_s21_qp_23 Q1(b); 9701_m20_qp_22 Q2(b)(i)

12 Nitrogen And Sulfur

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
25%	11/44	15	SO₂ acid rain	1. SO₂ reacts with water to form H₂SO₃ 2. SO₂ / H₂SO₃ can be oxidised to H₂SO₄ 3. these acids cause acid rain	9701_w21_qp_23 Q1(d)(ii); 9701_w21_qp_21 Q1(d)(ii); 9701_s20_qp_22 Q2(d); +3 additional hits
20%	9/44	11	NOₓ / atmospheric pollution	1. NOₓ forms when N₂ and O₂ react at high temperature in an internal combustion engine / lightning 2. NO/NO₂ reacts with oxygen and/or water/moist air to form HNO₂/HNO₃ and cause acid rain 3. NO/NO₂ can act as a homogeneous catalyst in SO₂ oxidation to SO₃ and is regenerated 4. NO₂/NOₓ reacts with unburned hydrocarbons/VOCs to form photochemical smog / PAN	9701_s24_qp_23 Q2(d)(i-ii); 9701_s23_qp_21 Q5(b)(i-iii); 9701_s22_qp_21 Q2(b)(i-ii); 9701_s20_qp_22 Q2(d); +5 additional hits
16%	7/44	7	photochemical smog / PAN	1. unburned/unburnt hydrocarbons / VOCs react or combine with NO and/or NO₂ 2. PAN / peroxyacetyl nitrate / peroxyacetylnitrate is formed 3. PAN is a component of photochemical smog	9701_s25_qp_23 Q3(a)(ii); 9701_s24_qp_23 Q2(d)(ii); 9701_s22_qp_21 Q2(b)(i); 9701_m22_qp_22 Q2(d)(ii); +3 additional hits
11%	5/44	7	ammonium ion / ammonium salts	1. NH₄⁺ / ammonium ion is a Brønsted-Lowry acid / proton donor 2. NH₄⁺ + OH⁻ → NH₃ + H₂O; use alkali/NaOH and heat/warm to liberate NH₃ from ammonium salts 3. NH₃ accepts H⁺ using the lone pair on N; in NH₄⁺ there are four N-H bonds, one may be shown as coordinate when the formation is asked	9701_s24_qp_23 Q4(a-b); 9701_w22_qp_22 Q1(c)(ii); 9701_s22_qp_21 Q2(c); +2 additional hits
9%	4/44	4	N₂ lack of reactivity	1. N₂ molecules have a strong N≡N triple covalent bond / high N≡N bond enthalpy 2. high activation energy / much energy is needed to break the N≡N bond 3. N₂ molecules are non-polar 4. in comparison questions, P≡P is much weaker, so P₂ is more reactive than N₂	9701_w24_qp_22 Q3(f)(ii); 9701_s24_qp_23 Q1(a)(i); 9701_m24_qp_22 Q3(a); 9701_m21_qp_22 Q3(a)(ii)
9%	4/44	4	ammonia / Bronsted base	1. NH₃ is a Bronsted-Lowry base/proton acceptor 2. the lone pair on N accepts H⁺	9701_w24_qp_22 Q3(b)(iii)
2%	1/44	1	homogeneous catalyst	1. homogeneous catalyst is in the same phase/state as the reactants 2. it increases rate / lowers Ea 3. it is regenerated / chemically unchanged overall	9701_s20_qp_21 Q3(e)(i)

13 Introduction To AS Organic Chemistry

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
43%	19/44	14	σ/π bond counting and hybridisation in organic molecules	1. count every single bond as one σ bond 2. each C=C contains one σ bond and one π bond; each C≡N/C≡C contains one σ bond and two π bonds 3. π bonds are formed by sideways/lateral overlap of p orbitals 4. sp² centres are trigonal planar around C=C; sp³ centres are tetrahedral around saturated carbon	9701_s24_qp_21 Q4(b)(i-ii); 9701_s23_qp_22 Q3(c); 9701_s20_qp_23 Q4(d)(ii); +16 additional hits
18%	8/44	8	structural isomerism	1. same molecular formula but different structural formulae	9701_w22_qp_22 Q3(a)(ii); 9701_w22_qp_21 Q3(d)(iv); 9701_s21_qp_23 Q5(d); +6 additional hits
16%	7/44	7	stereoisomerism	1. same structural formula but different spatial arrangement of atoms/groups	9701_w22_qp_23 Q5(a)(iii); 9701_w22_qp_21 Q5(a)(iii); 9701_w21_qp_22 Q3(e)(iv); +8 additional hits
11%	5/44	5	geometrical isomerism	1. restricted rotation about C=C 2. each carbon atom in the C=C has two different groups attached	9701_s20_qp_23 Q5(a)(iii); 9701_s20_qp_22 Q2(c)(ii); 9701_m20_qp_22 Q3(d)(i); +7 additional hits
9%	4/44	4	chiral centre / optical isomerism	1. chiral carbon/centre is bonded to four different groups 2. enantiomers are non-superimposable mirror images	9701_s21_qp_23 Q5(b)(i); 9701_s20_qp_23 Q3(b)(ii); 9701_m20_qp_22 Q3(a)(iv); +8 additional hits
2%	1/44	1	functional group	1. for identification questions, name the functional group exactly 2. definition: atom or group of atoms responsible for the characteristic reactions of the compound	9701_s21_qp_22 Q5(b)(iv); 9701_s21_qp_22 Q4(d)(ii); 9701_s20_qp_23 Q5(b)(i); +4 additional hits

14 Hydrocarbons

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
27%	12/44	12	major product / carbocation stability	1. major product forms via the more stable carbocation/intermediate 2. more alkyl groups give greater positive inductive effect/electron donation 3. positive charge is spread/stabilised more	9701_s20_qp_21 Q5(d)(ii); 9701_s20_qp_21 Q5(d)(i); 9701_m20_qp_22 Q3(c)(iii); +30 additional hits
23%	10/44	13	alkene test	1. bromine water / Br₂(aq) is decolourised from orange/brown to colourless	9701_s22_qp_22 Q6(a); 9701_s21_qp_21 Q5(c)(ii); 9701_s21_qp_21 Q4(b); +7 additional hits
18%	8/44	25	radical substitution mechanism	1. initiation: homolytic fission in UV light forms halogen radicals 2. propagation 1: a halogen radical removes H from an alkane to form an alkyl radical and HCl/HBr 3. propagation 2: the alkyl radical reacts with Cl2/Br2 to form a halogenoalkane and regenerate a halogen radical 4. termination: two radicals combine to form a stable molecule	9701_w24_qp_21 Q2(b)(iii); 9701_m21_qp_22 Q2(g)(i); 9701_s20_qp_23 Q4(b)(ii); +22 additional hits
7%	3/44	3	addition reaction definition	1. two or more molecules combine to form a single product 2. no atoms are lost	9701_w20_qp_23 Q4(b)(ii); 9701_w20_qp_21 Q4(b)(ii); 9701_s20_qp_22 Q5(a); +3 additional hits
7%	3/44	3	free radical definition	1. species with one or more unpaired electrons	9701_w24_qp_23 Q2(b)(i); 9701_w24_qp_21 Q2(b)(i); 9701_w23_qp_22 Q2(e)(i)
5%	2/44	2	incomplete combustion pollutants	1. incomplete combustion can produce C/soot, CO and unburnt/unburned hydrocarbons, with less/no CO₂ 2. CO is toxic/poisonous/harmful to health 3. unburnt/unburned hydrocarbons can catalyse/contribute to photochemical smog	9701_s23_qp_21 Q5(a)(ii); 9701_s21_qp_21 Q5(e)(ii)
5%	2/44	3	homolytic fission / radical formation	1. ultraviolet light supplies energy for homolytic fission 2. the covalent bond breaks evenly so each atom/species receives one electron 3. radicals with unpaired electrons are formed	9701_s22_qp_22 Q4(b)(ii); 9701_s20_qp_21 Q5(b)(ii); 9701_s20_qp_21 Q5(b)(i)
2%	1/44	1	alkane combustion / cracking	1. complete combustion forms CO₂ and H₂O 2. cracking uses heat and a catalyst such as Al₂O₃/SiO₂ to form a shorter alkane and an alkene	9701_s20_qp_23 Q1(b)(i); 9701_s20_qp_21 Q6(f)(i); 9701_s20_qp_21 Q4(c); +20 additional hits

15 Halogen Compounds

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
9%	4/44	4	nucleophilic substitution	1. curly arrow from lone pair/electron pair on the nucleophile to the electron-deficient carbon 2. curly arrow from the C-X bond to X as the C-X bond breaks 3. halide ion leaves	9701_s21_qp_22 Q3(c)(i); 9701_w20_qp_23 Q4(c)(ii); 9701_w20_qp_21 Q4(c)(ii); +2 additional hits
5%	2/44	2	C-X bond strength and hydrolysis rate	1. C-I has lower bond enthalpy / is weaker than C-Cl 2. I is larger, so the shared pair is less strongly attracted to the iodine nucleus 3. less energy is needed to break C-I / form the carbocation, so Ea is lower 4. hydrolysis/substitution is faster	9701_s22_qp_22 Q5(b); 9701_s21_qp_22 Q3(d)

16 Hydroxy Compounds

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
5%	2/44	2	iodoform reaction	1. a CH₃CO- or CH₃CH(OH)- group is present 2. alkaline aqueous iodine / I₂ and NaOH is used 3. yellow precipitate of CHI₃ forms	9701_s22_qp_21 Q4(c)(ii); 9701_w20_qp_23 Q4(c)(vi); 9701_w20_qp_21 Q4(c)(vi); +2 additional hits
2%	1/44	1	Na with alcohol	1. alcohol reacts with Na to give effervescence of H₂ and sodium alkoxide 2. Na is oxidised from 0 to +1	9701_s20_qp_22 Q4(c)(ii); 9701_s20_qp_22 Q1(e)(ii); 9701_s20_qp_21 Q4(c); +59 additional hits
2%	1/44	1	alcohol oxidation conditions/products	1. primary alcohol + acidified K₂Cr₂O₇/KMnO₄: distil to aldehyde 2. primary alcohol + acidified K₂Cr₂O₇/KMnO₄: reflux to carboxylic acid 3. secondary alcohol refluxes to ketone 4. tertiary alcohol shows no oxidation	9701_s21_qp_23 Q5(b)(ii); 9701_m21_qp_22 Q4(c)(ii)
2%	1/44	1	tertiary alcohol oxidation	1. tertiary alcohol is not oxidised because there is no H attached to the carbon bearing the -OH group	9701_s21_qp_23 Q5(b)(ii)

17 Carbonyl Compounds

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
23%	10/44	10	2,4-DNPH test	1. 2,4-DNPH gives a red/orange/yellow precipitate with carbonyl compounds (aldehydes/ketones)	9701_s21_qp_23 Q4(b); 9701_w20_qp_22 Q4(c); 9701_s20_qp_21 Q6(d); +10 additional hits
20%	9/44	9	Tollens / Fehling distinction	1. aldehydes reduce Tollens’ reagent to a silver mirror/grey precipitate 2. aldehydes reduce Fehling’s solution to a brick-red precipitate 3. ketones show no visible change	9701_m22_qp_22 Q4(a)(i); 9701_m21_qp_22 Q4(b); 9701_w20_qp_22 Q4(a)(iv); +6 additional hits
9%	4/44	4	HCN nucleophilic addition mechanism	1. curly arrow from the lone pair on CN⁻ to the δ⁺ carbonyl carbon 2. curly arrow from the C=O π bond to O 3. O⁻/alkoxide is protonated by HCN/H⁺ to form the hydroxynitrile	9701_w20_qp_23 Q3(c)(iii); 9701_w20_qp_21 Q3(c)(iii); 9701_s20_qp_22 Q5(b)(i); +8 additional hits
7%	3/44	3	carbonyl reduction	1. NaBH₄ or LiAlH₄ reduces aldehydes to primary alcohols and ketones to secondary alcohols	9701_w20_qp_23 Q3(c)(ii); 9701_w20_qp_22 Q3(c)(i); 9701_w20_qp_21 Q3(c)(ii); +5 additional hits
2%	1/44	1	aldehyde oxidation	1. aldehydes oxidise to carboxylic acids 2. ketones are not oxidised under these conditions	9701_s21_qp_22 Q4(d)(ii)

18 Carboxylic Acids And Derivatives

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
14%	6/44	6	carboxylic acid + carbonate/metal	1. carbonate/hydrogencarbonate gives effervescence of CO₂ 2. CO₂ turns limewater milky if tested 3. reactive metal gives effervescence of H₂ and a salt	9701_m25_qp_22 Q2(d)(i); 9701_s23_qp_23 Q5(d); 9701_s22_qp_21 Q4(b)(i)
11%	5/44	5	esterification	1. carboxylic acid + alcohol with concentrated H₂SO₄ catalyst and heat/reflux forms ester + water	9701_w21_qp_22 Q3(e)(v); 9701_w20_qp_22 Q4(a)(v); 9701_m20_qp_22 Q3(a)(v)
2%	1/44	1	ester hydrolysis	1. dilute acid + heat/reflux gives carboxylic acid + alcohol 2. NaOH(aq) + heat gives carboxylate + alcohol 3. acidification gives the carboxylic acid	9701_s21_qp_23 Q4(c)

19 Nitrogen Compounds

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
23%	10/44	10	nitrile hydrolysis to carboxylic acid / carboxylate	1. acid hydrolysis: RCN + 2H₂O + HCl/H⁺ → RCOOH + NH₄Cl/NH₄⁺ 2. alkaline hydrolysis: RCN + 2H₂O + NaOH → RCO₂Na + NH₄OH/NH₃; acidification gives RCOOH if required 3. heat/reflux with dilute acid or aqueous alkali 4. the nitrile carbon becomes the carboxyl carbon, so the carbon chain length does not change during hydrolysis	9701_s25_qp_24 Q4(d)(i); 9701_s22_qp_22 Q5(c)(ii); 9701_w20_qp_21 Q3(c)(iv); +7 additional hits
9%	4/44	4	hydroxynitrile preparation	1. aldehyde/ketone + HCN with KCN/NaCN catalyst 2. CN⁻ nucleophilic addition forms a hydroxynitrile	9701_m25_qp_22 Q4(b)(ii)

20 Polymerisation

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
7%	3/44	3	repeat unit drawing	1. one repeat unit with correct carbon backbone and continuation/dangling bonds	9701_w22_qp_23 Q4(d)(ii); 9701_w22_qp_22 Q3(b)(ii); 9701_w22_qp_21 Q4(d)(ii)
2%	1/44	1	addition polymerisation definition	1. alkene monomers join as C=C bonds open 2. no small molecule is eliminated	9701_m21_qp_22 Q3(d)(i)
2%	1/44	1	polymer disposal	1. addition polymers are often non-biodegradable 2. combustion of chlorine-containing polymers can produce HCl/toxic gases	9701_s22_qp_22 Q4(c)(ii)

21 Organic Synthesis

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
41%	18/44	18	oxidation/reduction route	1. choose reagent and conditions from the functional group 2. acidified K₂Cr₂O₇/KMnO₄ with distil/reflux for alcohols/aldehydes 3. NaBH₄ or LiAlH₄ for carbonyl reduction	9701_w20_qp_21 Q3(c)(i); 9701_s20_qp_22 Q5(a); 9701_m20_qp_22 Q3(a)(i); +22 additional hits
5%	2/44	2	multi-step route reagents/conditions	1. state reagent and condition for every step, and name the reaction type when asked 2. each is often a separate mark	9701_s20_qp_22 Q5(a)

22 Analytical Techniques

Frequency	Papers	MS hits	Point	Full-mark wording	Sources
36%	16/44	17	IR absorption identification	1. quote the absorption range in cm⁻¹ 2. state the bond responsible 3. state the functional group responsible 4. use presence/absence of O-H, C=O, C≡N etc. as evidence	9701_w20_qp_21 Q3(c)(v); 9701_s20_qp_21 Q6(e); 9701_m20_qp_22 Q3(d)(iii); +17 additional hits
11%	5/44	5	M+1 carbon count	1. use the abundance of the [M+1]⁺ peak 2. number of carbon atoms = abundance of [M+1]⁺ peak / (1.1 × abundance of M⁺ peak)	9701_w25_qp_21 Q4(c)(iii); 9701_s23_qp_23 Q5(c); 9701_s23_qp_21 Q4(b)(iii); +1 additional hits
7%	3/44	3	molecular ion peak	1. molecular ion peak M⁺ gives the Mr / molecular mass	9701_s22_qp_23 Q5(b)(ii); 9701_s22_qp_22 Q6(c)(i)
5%	2/44	2	relative atomic mass from isotopes	1. relative atomic mass = sum of isotope mass × fractional abundance 2. divide percentage abundances by 100	9701_s22_qp_21 Q1(e)(ii); 9701_s20_qp_23 Q2(b); 9701_s20_qp_21 Q1(a)(ii); +5 additional hits

Reading The Statistics

High frequency means the wording recurs often in recent P2 mark schemes, not that lower-frequency syllabus definitions can be ignored.
Low-frequency but explicit syllabus definitions still need to be memorised exactly.
For inorganic equations, organic synthesis routes and observations, the same exam skill is split across many substance-specific mark schemes, so this table may underestimate the real importance of the topic type.

Appendix: Syllabus / Low-Frequency Supporting Points

以下条目保留 syllabus/textbook/core review points，或属于具体路线/基础技能而未放入主表高频排序。Freq / Papers / MS hits 按当前 2020-2025 P2 MS 来源校正；no 2020-2025 P2 MS hit 表示本轮统计范围内没有 recent P2 MS 来源。

Section	Freq	Papers	MS hits	Point	Full-mark wording	Sources
1 Atomic Structure / Electrons In Atoms	2%	1/44	1	first ionisation energy definition	1. energy required when one electron is removed 2. from each atom in one mole of gaseous atoms	9701_s22_qp_23 Q1(a)
1 Atomic Structure / Electrons In Atoms	0%	0/44	0	ground state definition	1. lowest energy arrangement of electrons	no 2020-2025 P2 MS hit
2 Atoms, Molecules And Stoichiometry	0%	0/44	0	limiting reagent	1. reagent used up first according to the stoichiometric ratio	no 2020-2025 P2 MS hit
4 States Of Matter	0%	0/44	0	vapour pressure definition	1. pressure exerted by vapour in equilibrium with liquid at a stated temperature in a closed system	no 2020-2025 P2 MS hit
5 Chemical Energetics	0%	0/44	0	Hess law cycle/signs	1. reverse arrows change the sign of ΔH 2. multiply ΔH by coefficients when equations are multiplied 3. combine steps to obtain the target ΔH	no 2020-2025 P2 MS hit
5 Chemical Energetics	2%	1/44	1	enthalpy change of neutralisation	1. enthalpy/energy change when one mole of water is formed 2. from an aqueous acid and an aqueous alkali/base	9701_s24_qp_21 Q2(c)(iii)
8 Reaction Kinetics	0%	0/44	0	surface area effect	1. larger surface area exposes more particles, increasing the frequency of successful/effective collisions	no 2020-2025 P2 MS hit
10 Group 2	0%	0/44	0	Group 2 reactivity trend	1. down Group 2, shielding and distance of the outer electron from the nucleus increase 2. nuclear attraction for the outer electron decreases / first and second ionisation energies decrease 3. electrons are lost more readily, so reactivity increases	no 2020-2025 P2 MS hit
11 Group 17	5%	2/44	2	hydrogen halide thermal stability	1. H-X covalent bond strength decreases down the group 2. X atom is larger / H-X bond is longer, so there is weaker attraction between the nucleus and the shared pair 3. less energy is needed to break the bond, so thermal stability decreases	9701_w24_qp_23 Q2(a)(iv); 9701_w24_qp_21 Q2(a)(iv)
12 Nitrogen And Sulfur	20%	9/44	9	Contact/Haber equilibrium conditions	1. link temperature to exothermic/endothermic direction and equilibrium shift/yield 2. link pressure to the side with fewer moles of gas 3. chosen conditions are a compromise between yield, rate and cost	9701_w21_qp_23 Q1(d)(i); 9701_w21_qp_21 Q1(d)(i); 9701_s20_qp_21 Q3(e)(ii); +6 additional hits
13 Introduction To AS Organic Chemistry	0%	0/44	0	hydrocarbon definition	1. compound containing carbon and hydrogen only	no 2020-2025 P2 MS hit
13 Introduction To AS Organic Chemistry	0%	0/44	0	homologous series definition	1. same functional group and same general formula 2. successive members differ by CH₂ and have similar chemical properties	no 2020-2025 P2 MS hit
15 Halogen Compounds	16%	7/44	7	KCN chain extension	1. reagent is KCN/NaCN 2. condition is ethanol/alcohol and heat under reflux 3. nucleophilic substitution forms a nitrile and increases the carbon chain by one	9701_s23_qp_22 Q3(a)(i); 9701_s21_qp_23 Q4(c); 9701_s21_qp_22 Q5(b)(iii); +4 additional hits
15 Halogen Compounds	5%	2/44	2	NH₃ to amine	1. reagent is excess NH₃/ammonia 2. condition is ethanol/alcohol with heat under pressure / sealed tube 3. nucleophilic substitution forms a primary amine	9701_s24_qp_23 Q4(e)(iii); 9701_m21_qp_22 Q3(d)(iii)
15 Halogen Compounds	5%	2/44	2	aqueous vs ethanolic NaOH	1. hot aqueous NaOH gives nucleophilic substitution to an alcohol 2. NaOH/KOH in ethanol/alcohol and heat under reflux gives elimination to an alkene	9701_s22_qp_22 Q5(a); 9701_m22_qp_22 Q4(b)(iv)
15 Halogen Compounds	2%	1/44	1	tertiary halogenoalkane definition	1. the carbon atom bonded to the halogen atom is attached directly to three alkyl groups / three carbon atoms	9701_s20_qp_21 Q5(c)(ii)
16 Hydroxy Compounds	0%	0/44	0	alcohol acidity	1. alcohols are weaker acids than water because alkyl groups donate electron density, making RO- less stable	no 2020-2025 P2 MS hit
18 Carboxylic Acids And Derivatives	9%	4/44	4	carboxylic acid acidity	1. carboxylate ion is stabilised 2. negative charge is delocalised over the two oxygen atoms 3. the conjugate base is more stable, so the acid donates H⁺ more readily	9701_w21_qp_21 Q4(b); 9701_w20_qp_23 Q3(c)(ii); 9701_w20_qp_21 Q3(c)(ii); +1 additional hits
19 Nitrogen Compounds	11%	5/44	5	amine basicity	1. lone pair on N accepts H⁺ / a proton 2. the lone pair forms a dative bond to H⁺ 3. alkyl groups donate electron density to N if comparing basicity	9701_w24_qp_21 Q4(a)(i); 9701_s23_qp_23 Q6(b)(ii); 9701_m23_qp_22 Q3(b)(i); +2 additional hits
19 Nitrogen Compounds	16%	7/44	7	nitrile preparation	1. reagent is KCN/NaCN 2. condition is ethanol/alcohol and heat under reflux 3. nucleophilic substitution of a halogenoalkane forms a nitrile	9701_s23_qp_22 Q3(a)(i); 9701_s21_qp_23 Q4(c); 9701_s21_qp_22 Q5(b)(iii); +4 additional hits
19 Nitrogen Compounds	2%	1/44	1	primary amine preparation	1. reagent is excess NH₃/ammonia 2. condition is ethanol/alcohol with heat under pressure / sealed tube 3. nucleophilic substitution forms a primary amine	9701_s24_qp_23 Q4(c)(ii)
20 Polymerisation	0%	0/44	0	monomer from polymer	1. identify the repeat unit 2. then put C=C back between the two backbone carbon atoms to get the alkene monomer	no 2020-2025 P2 MS hit
21 Organic Synthesis	0%	0/44	0	functional group identification	1. use syllabus tests/reactions to identify functional groups before choosing a route 2. concrete functional-group naming, IR and chemical-test questions are counted in their own rows	no 2020-2025 P2 MS hit
21 Organic Synthesis	0%	0/44	0	by-products	1. analyse possible inorganic/organic by-products from substitution, elimination or hydrolysis	no 2020-2025 P2 MS hit
22 Analytical Techniques	2%	1/44	1	Cl/Br M+2 pattern	1. one Cl gives M:M+2 about 3:1 because M+2 contains ³⁷Cl instead of ³⁵Cl 2. one Br gives M:M+2 about 1:1 because ⁷⁹Br and ⁸¹Br have similar abundance	9701_s22_qp_23 Q5(b)(ii)
22 Analytical Techniques	5%	2/44	2	fragment ion formula	1. assign each m/e or m/z peak to a possible fragment ion 2. include the positive charge on the fragment ion 3. use isotope composition where M/M+2 peaks are involved	9701_s25_qp_21 Q2(b)(i); 9701_s23_qp_21 Q3(f)