CIE 9701 AS Chemistry Paper 3 实验技巧指引：真题 MS 优化版

使用顺序：先背高频动作和 wording，再用 Sources 回到原题核对实验场景。统计范围为 2020-2025 官方 9701 P3 QP/MS，N = 69；Sources 按最新到最旧显示，+N older hits 表示还有更早来源未展开。

考试定位：CIE 9701 AS Chemistry Paper 3 是 Advanced Practical Skills 实验卷；考试时间 2 h，40 marks。它不是单纯背实验步骤，而是现场实验数据、观察、计算、定性分析和实验评价一起拿分。

Official syllabus: Cambridge 9701 Chemistry syllabus 2025-2027; Paper 3 is a practical test, 2 hours, 40 marks.

答题核心：先让 examiner 看见证据：raw data, headings, units, precision, observations by stage。再写 calculation / conclusion / ion identity。accuracy marks 依赖 supervisor value；qualitative analysis 必须写现象，不要只写离子名称。

Highest-Frequency First

Frequency	位置	Point	MS-ready action / wording	Sources
78% 54/69	Q1 / Q2	Titration + mean titre	必须先拿记录分：rough、至少两次 accurate、initial/final/titre、cm³、0.05 cm³、concordant。再拿 calculation 分：mean titre 2 d.p.、n = cV、stoichiometric ratio。	w25/38; w25/37; w25/36; +51 older hits
78% 54/69	Q1 / Q2	Redox titration	manganate(VII)、thiosulfate/iodine 是 P3 定量主线。先确认 half-equation / mole ratio，再代入 mean titre；若题目问酸体积，常见结论是 acid is in excess / exact volume is not important。	w25/38; w25/37; w25/36; +51 older hits
43% 30/69	Q1 / Q2	Mass / heating / hydrated salt	表头必须覆盖 empty crucible、crucible + solid、after first/second heating、mass of solid/residue/water lost。所有 weighings 同一 dp，x 通常取 closest integer。	w25/38; w25/37; w25/36; +27 older hits
43% 30/69	Q1 / Q2	Calorimetry / temperature	记录 initial 和 final / maximum / minimum temperature，ΔT 正确；thermometer readings 通常到 .0 或 .5 °C；energy = mass × 4.18 × ΔT；ΔH 注意正负号。	w25/34; w25/33; s25/38; +27 older hits
25% 17/69	Q1 / Q2	Dilution / volumetric flask	QP 中反复出现，MS 常把分给到后续滴定计算。25.0 cm³ → 250 cm³ 这类 dilution factor 必须单独乘回原溶液浓度。	s25/37; s25/33; s25/31; +14 older hits
84% 58/69	Q3	NaOH cation test	写 ppt colour、soluble / insoluble in excess、加热后 gas test。不要只写 ion name。	w25/38; w25/37; w25/36; +55 older hits
81% 56/69	Q3	NH3 cation test	白色沉淀体系 Al³⁺/Zn²⁺/Mg²⁺ 常靠 excess NH3 / excess NaOH 区分；Cu²⁺靠 deep blue solution。	w25/38; w25/37; w25/36; +53 older hits
71% 49/69	Q3	Redox qualitative tests	KI/starch、acidified KMnO4、H2O2/MnO2、Fe²⁺/Fe³⁺经常作为同一张 Q3 的 redox strand。现象必须写 colour change + gas / starch result。	w25/38; w25/37; w25/36; +46 older hits
51% 35/69	Q3	Carbonate / CO2	acid + carbonate: effervescence; gas turns limewater milky / gives white precipitate with limewater。只写 carbonate present 不够。	w25/38; w25/36; w25/34; +32 older hits
51% 35/69	Q3	Halide / AgNO3	acidified AgNO3 后写 ppt colour，再写 solubility in NH3。Cl⁻ white soluble in dilute NH3; Br⁻ cream partly soluble in conc NH3; I⁻ yellow insoluble。	w25/34; s25/32; s25/31; +32 older hits

颜色 / 沉淀 / 滴定终点色卡 Colour and Precipitate Quick Visuals

颜色题先写 MS 认可的颜色词，再补状态或沉淀。渐变色卡提醒：溶液稀、气体少、沉淀量小时颜色会变浅；答题仍写 pale yellow、yellow-green、orange-brown、violet 这类可给分词。

Titration endpoints 滴定终点

manganate(VII): permanent pale pink, not deep purple

iodine + starch: blue-black; thiosulfate endpoint becomes colourless

Acid-base indicators 酸碱指示剂终点

→methyl orange / 甲基橙，acid into alkali / 酸滴入碱: yellow → orange at endpoint; red if excess acid

→methyl orange / 甲基橙，alkali into acid / 碱滴入酸: red → orange at endpoint; yellow if excess alkali

→litmus / 石蕊，acid into alkali / 酸滴入碱: blue → purple at neutral endpoint; red if excess acid

→litmus / 石蕊，alkali into acid / 碱滴入酸: red → purple at neutral endpoint; blue if excess alkali

→phenolphthalein / 酚酞，acid into alkali / 酸滴入碱: pink → colourless; endpoint is when pink just disappears

→phenolphthalein / 酚酞，alkali into acid / 碱滴入酸: colourless → permanent very pale pink

→thymolphthalein / 百里酚酞，acid into alkali / 酸滴入碱: blue → colourless; endpoint is loss of blue colour

→thymolphthalein / 百里酚酞，alkali into acid / 碱滴入酸: colourless → pale blue

Direction wording means the first-named solution is in the burette and is added to the second solution in the flask.

Halide precipitates 卤化银沉淀

Cl⁻: white precipitate, soluble in dilute NH₃

Br⁻: MS wording = cream precipitate; visually can look off-white / pale cream, partly soluble in concentrated NH₃

I⁻: MS wording = yellow precipitate; visually can look pale yellow to yellow, insoluble in NH₃

考试作答仍优先用 MS 词：Cl⁻ white, Br⁻ cream, I⁻ yellow；真实沉淀量少或悬浊液很稀时，Br⁻ / I⁻ 都可能显得偏浅。

Halogens at room temperature 卤素单质常温状态

F₂(g): pale yellow gas

Cl₂(g): yellow-green / pale green gas

Br₂(l): red-brown / orange-brown liquid at room temperature

Br₂(g): red-brown / orange-brown vapour above bromine liquid

I₂(s): grey-black / dark grey solid at room temperature

I₂(g): purple / violet vapour on warming / sublimation

若题目问 appearance，要同时写 colour + state；Br₂ 和 I₂ 可能同时看到 condensed phase 和 vapour，作答时按题目观察对象分别写。AS 常用 F₂, Cl₂, Br₂, I₂，不把 astatine 作为 P3 常规观察点。

Concentration-sensitive colour intensity 浓度相关色深

F₂(g): very pale yellow → pale yellow; low concentration can be difficult to see

Cl₂(g): very pale green → yellow-green / greenish gas

Br₂(l) / Br₂(g): orange-brown → red-brown; vapour may look faint if dilute

I₂(g): pale violet → purple / violet vapour on warming

iodine solution: yellow-brown / brown; darker with higher iodine concentration

acidified KMnO₄: pale purple → purple; reducing agent decolourises / turns colourless

Cu²⁺ / deep blue NH₃ complex: pale blue → blue / deep blue solution

Fe²⁺ ppt on standing: green can darken / turn brown on oxidation

颜色偏淡时也要落到可给分词：pale yellow, yellow-green, orange-brown, red-brown, violet, brown, purple, pale blue, deep blue。

Cation precipitates 阳离子沉淀

Cu²⁺: blue / pale blue precipitate; deep blue solution in excess NH₃

Fe²⁺: green precipitate, may turn brown on standing

Fe³⁺: brown / red-brown precipitate

Al³⁺ / Zn²⁺ / Mg²⁺: white precipitate; distinguish by solubility in excess NaOH / NH₃

Common colour changes 常见颜色变化

acidified KMnO₄: purple decolourised / turns colourless by reducing agent

iodine: brown / yellow-brown; starch gives blue-black

CO₂ + limewater: turns milky / gives white precipitate

Salt Solubility and Precipitate Colours 盐类溶解性与沉淀颜色

P3 用这个表主要服务于 Q3 qualitative analysis：先判断是否应该有 precipitate，再写颜色。颜色以 CAIE MS 常用词为主；真实观察可能因沉淀量、浓度和背景颜色略有偏浅。

Salt type	Usually soluble	Insoluble / sparingly soluble in P3	Precipitate colour to write
Sodium, potassium and ammonium salts 钠盐、钾盐、铵盐	All	None expected from this rule	No precipitate from solubility rule
Nitrates 硝酸盐	All	None expected	No precipitate from nitrate solubility
Chlorides 氯化物	Most chlorides	AgCl; PbCl₂ is sparingly soluble / dissolves better in hot water	AgCl white; PbCl₂ white
Bromides 溴化物	Most bromides	AgBr; PbBr₂	AgBr cream / off-white; PbBr₂ white to cream
Iodides 碘化物	Most iodides	AgI; PbI₂	AgI yellow / pale yellow; PbI₂ yellow
Sulfates 硫酸盐	Most sulfates	BaSO₄, PbSO₄ insoluble; CaSO₄ sparingly soluble	BaSO₄ / PbSO₄ / CaSO₄ white
Carbonates 碳酸盐	Na₂CO₃, K₂CO₃ and (NH₄)₂CO₃	Most other carbonates	most white; CuCO₃ green / blue-green if seen
Hydroxides 氢氧化物	NaOH, KOH and NH₄OH / aqueous ammonia; Ca(OH)₂ is sparingly soluble	Most other metal hydroxides	Al³⁺/Zn²⁺/Mg²⁺ white; Cu²⁺ blue; Fe²⁺ green; Fe³⁺ brown / red-brown

Precipitate group	P3 examples	Colour / observation
Silver halides	AgCl, AgBr, AgI after acidified AgNO₃	AgCl white; AgBr cream / off-white; AgI yellow / pale yellow. Then use NH₃ solubility to distinguish.
Lead(II) salts	PbCl₂, PbI₂, PbSO₄	PbCl₂ white; PbI₂ yellow; PbSO₄ white. PbCl₂ may dissolve better in hot water.
Sulfate test	Ba²⁺ + SO₄²⁻ → BaSO₄	white precipitate; usually tested after acidifying to remove carbonate interference.
Carbonate test	metal carbonate + acid	effervescence; CO₂ turns limewater milky / gives white precipitate. Solid carbonate colours can vary, but gas test is decisive.
Hydroxide test with NaOH / NH₃	Al³⁺, Zn²⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺, Fe³⁺	white for Al/Zn/Mg/Ca; blue for Cu²⁺; green for Fe²⁺, may turn brown on standing; brown / red-brown for Fe³⁺.

一张卷子的得分逻辑

P3 通常是两个 quantitative experiments 加一个 qualitative analysis。Q1/Q2 的分工不固定：任一题都可能是 titration、calorimetry、mass/heating、gas/rate 或 dilution-linked calculation。

P3 给分看 visible evidence：数据、单位、精度、计算步骤和分阶段 observation 都必须写在卷面上。

Accuracy marks 只奖励接近 supervisor value 的结果；如果表格、精度、subtraction 或 mean selection 错了，即使化学思路正确也会丢分。

Qualitative analysis 的 observation 分通常先于 conclusion 分；先写现象，再写 ion / reagent / equation。

Representative Question Cards / 代表题拆解卡片

每张卡片只保留该题型最常丢分的 MS 点。复习时先按卡片检查答案，再回来源卷核对题目条件。

78%
54/69 · w25/38; w25/37; w25/36; +51 older hits

Titration recording + mean titre

MS mark points

table has initial/final/titre headings and cm³ units
rough titre is recorded but not used in mean
accurate burette readings are to 0.05 cm³
mean uses concordant accurate titres and is quoted to 2 d.p.

Exam-safe wording: Use two or more accurate titres with total spread not more than 0.20 cm³; mean titre = selected accurate titres only.

Do not write: Do not write only “average titre”. Do not include rough titre in the mean.

43%
30/69 · w25/34; w25/33; s25/38; +27 older hits

Calorimetry / temperature table

MS mark points

initial temperature and final / maximum / minimum temperature are visible
thermometer readings are to .0 or .5 °C
temperature change is calculated from the readings
energy calculation uses mass × 4.18 × ΔT and ΔH has the correct sign

Exam-safe wording: The temperature rise is lower than the true value, so the calculated energy released / enthalpy change is smaller in magnitude.

Do not write: Do not write only “heat loss makes it inaccurate”. State the consequence.

43%
30/69 · w25/38; w25/37; w25/36; +27 older hits

Mass / heating / hydrated salt

MS mark points

mass headings identify crucible, solid, residue, first heating and second heating
all weighings use the same number of decimal places
mass loss / water lost is calculated by subtraction
hydrate number is calculated from mole ratio and given as the closest integer

Exam-safe wording: Heat, cool and weigh again; repeat until the mass is constant.

Do not write: Do not write only “heat more”. Mention constant mass or repeated heating/cooling/weighing.

84%
58/69 · w25/38; w25/37; w25/36; +55 older hits

Qualitative analysis observation writing

MS mark points

observations are written by stage: on addition, in excess, on heating, on standing
precipitate colour and solubility in excess are both stated
gas test result is stated, not only the gas identity
no change / no precipitate is written when there is no visible observation

Exam-safe wording: A pale blue precipitate forms, soluble in excess aqueous ammonia to give a deep blue solution.

Do not write: Do not replace observations with “Cu²⁺ present”. Observation marks usually come first.

19%
13/69 · w25/33; w24/34; w24/33; +10 older hits

Gas collection / rate table

MS mark points

time / s and gas volume / cm³ headings are present
readings are recorded at regular intervals if the question asks for a rate graph
rate comparison uses initial gradient or volume/time as required
gas identity is supported by a test result

Exam-safe wording: The rate is greater because the initial gradient of the volume-time graph is steeper.

Do not write: Do not write “more gas is produced faster” without referring to time, volume or gradient.

High-Frequency MS Rules

Frequency	Mark type	Rule	Full-mark wording	Sources
78% 54/69	Recording	Titration table headings	initial / start burette reading, final / end burette reading, titre / volume added; units as / cm³, (cm³), in cm³, or cm³ beside every volume.	w25/38; w25/37; w25/36; +51 older hits
75% 52/69	Accuracy	Concordant accurate titres	The final accurate titre recorded must be within 0.10 cm³ of another accurate titre. Do not use a reading labelled rough.	w25/38; w25/37; w25/36; +49 older hits
62% 43/69	Processing	Mean titre	Use two or more accurate titres with total spread not more than 0.20 cm³; show ticks or working; quote the mean to 2 d.p. / nearest 0.01 cm³.	w25/38; w25/37; w25/36; +40 older hits
55% 38/69	Recording	Minimum titration data	Record two burette readings and a rough titre, plus initial and final readings for at least two accurate titrations.	w25/38; w25/37; w25/36; +35 older hits
52% 36/69	Processing	Significant figures	Final calculation answers commonly need 3 or 4 significant figures; do not round intermediate values too early.	w25/38; w25/36; w25/34; +33 older hits
36% 25/69	Recording	Thermometer precision	All thermometer readings to .0 or .5 °C; temperature change / rise / fall must be calculated from the recorded readings.	w25/33; s25/38; s25/37; +22 older hits
35% 24/69	Recording	Balance precision	All weighings to the same number of decimal places, usually 2 or 3 d.p.; mass by difference must be correctly subtracted.	w25/38; w25/37; w25/36; +21 older hits
29% 20/69	Processing	Calorimetry energy	energy change = mass of solution × 4.18 × temperature change; answer usually to 2-4 s.f.	w25/34; w25/33; s25/38; +17 older hits

Apparatus Precision

Apparatus	Required recording	Exam-safe example	Where it matters
Burette	accurate readings to 0.05 cm³	23.40, 23.45, 23.50 are acceptable; 23.43 is not a normal burette reading.	Titration recording / accuracy
Pipette	fixed volume	25.0 cm³; do not invent extra decimal places.	Volume used in calculation
Volumetric flask	fixed final volume	250 cm³ or 100 cm³ as printed; use dilution factor explicitly.	Dilution calculations
Thermometer	.0 or .5 °C	24.0, 24.5; ΔT calculated from readings.	Calorimetry / temperature
Balance	same 2 or 3 d.p.	all weighings consistent; mass by difference from table.	Mass / heating
Gas syringe	usually whole cm³ unless scale states otherwise	record time and gas volume in a table; keep units in headings.	Gas / rate experiments

Titration 满分流程

Step	Task	MS expects	Student action
1	Rough titration	initial reading + final reading + rough titre	粗滴不是用来算 mean 的，但没有 rough 数据会丢 recording。
2	Accurate titrations	at least two accurate initial/final readings	做 enough accurate titrations until concordant。
3	Precision	accurate burette readings to 0.05 cm³	所有 accurate 初末读数末位应为 0 或 5。
4	Concordance	final accurate titre within 0.10 cm³ of another	若没有 concordant titre，accuracy 与 mean 选择都会受影响。
5	Mean	average selected titres with spread ≤ 0.20 cm³; 2 d.p.	用 ticks 标出 selected titres，减少 examiner 误判。
6	Calculation	n = cV / 1000; apply mole ratio; scale to dm³	先写 unit，再代数字；dilution factor 另乘。

Titration 表格模板

Run	Initial burette reading / cm³	Final burette reading / cm³	Titre / cm³
Rough
1
2
3 if needed

mean titre 只从 selected accurate titres 计算；不要把 rough titre 放进 mean。

如果两组 accurate titres within 0.20 cm³ total spread，用 ticks 标明 selected titres，并把 mean rounded to nearest 0.01 cm³。

对 manganate(VII) 滴定，endpoint 常写为 permanent pale pink colour；对 iodine / thiosulfate 体系，注意 starch 的加入时机和蓝黑色消失/出现。

Table Drawing Examples: headings decide marks

P3 的表格分通常先看 heading 和 unit，再看数据精度和后续计算。下列表格可以直接作为考场模板；若题目已经给表格，仍按同样逻辑检查每一列。

Example 1: Titration results table

Run	Initial burette reading / cm³	Final burette reading / cm³	Titre / cm³	Use in mean?
Rough	0.00	24.80	24.80	No
1	0.05	24.70	24.65	Yes
2	0.00	24.65	24.65	Yes
3	0.10	24.75	24.65	Yes

Why this scores: every burette column has cm³; accurate readings end in 0 or 5; rough is separated; selected titres are concordant; mean = 24.65 cm³.

Common mistake: headings like `start / finish / amount` without unit, or averaging rough + accurate titres together.

Example 2: Calorimetry temperature table

Measurement	Temperature / °C	Precision check	How it is used
Initial temperature of solution	21.0	.0 or .5 °C	starting value
Maximum temperature reached	31.5	.0 or .5 °C	use maximum for exothermic reaction
Temperature rise	10.5	from readings	ΔT in q = mcΔT

If the reaction cools the solution, use minimum temperature and write temperature fall / decrease. Do not invent extra decimal places.

Example 3: Heating / hydrated salt table

Measurement	Mass / g	Calculation role	MS note
Mass of empty crucible + lid	18.42	subtract from later masses	same d.p. as all weighings
Mass of crucible + lid + hydrated salt	21.86	mass of hydrated salt	before heating
Mass after first heating	20.61	check water loss	cool before weighing
Mass after second heating	20.60	constant mass check	close to first heating
Mass of water lost	1.26	n(H2O) = mass / 18	show subtraction if asked

Common mistake: writing only `before` and `after` without saying crucible + solid or residue, so the examiner cannot see which mass was measured.

Example 4: Gas / rate table

Time / s	Volume of gas / cm³	Recording rule	Use
0	0	whole cm³ unless scale states otherwise	start
30	18	same unit in heading	plot point
60	31	regular time interval	plot point
90	40	keep readings consistent	initial gradient / rate comparison

For gas identity, the table is not enough. Write the gas test result separately: H2 pops, O2 relights glowing splint, CO2 turns limewater milky.

Example 5: Qualitative analysis observation table

Test stage	Reagent / condition	Observation	Possible conclusion
On adding	aqueous sodium hydroxide	blue precipitate	Cu²⁺ possible
In excess	excess aqueous sodium hydroxide	precipitate insoluble	supports Cu²⁺
On heating	warm with NaOH if NH4⁺ suspected	gas turns damp red litmus blue	NH4⁺ present
No visible change	after adding stated reagent	no precipitate / no change	negative observation still scores

Common mistake: writing `Cu²⁺` in the observation box. The observation box needs visible evidence first.

Calculation Templates

Experiment	Core formula	Full-mark handling	Common P3 use
Titration	n = cV / 1000	V 用 cm³ 时除以 1000；再按 equation ratio 转换。	mean titre, concentration, Mr, purity, water of crystallisation
Dilution	original concentration = diluted concentration × dilution factor	25.0 cm³ made up to 250 cm³ gives factor 10。	2020-2025 QP 中 17/69 命中 volumetric / dilution
Calorimetry	q = mcΔT; ΔH = ± q / n / 1000	若 reaction releases heat, ΔH usually negative；若 solution temperature falls, process/endothermic value positive。	energy change, enthalpy, comparison of methods
Hydrated salt	n(H2O) = mass loss / 18; n(anhydrous salt) = mass residue / Mr	x = n(H2O) / n(salt)，取 closest integer。	crucible / second heating / mass ratio
Gas	n(gas) = V / 24000 or V / molar volume stated	确认题目是否给 room-temperature molar gas volume；不要把 cm³ 当 dm³。	gas syringe / rate / stoichiometry

所有 volume in cm³ 进入 n = cV 前先除以 1000。

题目写 show your working 时，至少写出一个关键中间量；即使只问 final answer，也建议写 mole ratio，后面算错时更容易拿 ecf。

final answers 常见要求是 3 or 4 significant figures；mean titre 是 2 d.p.，不要混淆。

Calorimetry / Temperature

表格至少要能看出 initial temperature、final / maximum / minimum temperature、temperature change / rise / fall，以及 °C units。

thermometer readings 按 .0 或 .5 °C 记录；temperature change 必须由表内读数相减得到。

energy = mass × 4.18 × ΔT。若溶液体积近似等于质量，通常用题目给的 cm³ 数值作 g。

ΔH = ± energy / amount / 1000。exothermic 通常 negative；endothermic / temperature fall 通常 positive。

评价题不要只写 heat loss。要写 consequence：temperature change lower, energy released lower, calculated concentration / enthalpy affected, percentage error greater。

Mass / Heating / Hydrated Salt

常见 headings：mass of empty crucible / crucible + lid, mass of crucible + solid, mass after first heating, mass after second heating, mass of solid, mass of residue, mass loss / water lost。

all weighings to same decimal places，通常 2 或 3 d.p.。

second heating 的质量通常需要接近 first heating 后质量；若 mass after second heating 与 first heating 相差太大，说明未到 constant mass 或有实验误差。

hydrate calculation：n(H2O) = mass loss / 18；n(anhydrous salt) = mass residue / Mr；x = n(H2O) / n(salt)，final answer as closest integer。

技术语言：lid prevents solid / solution from spitting or frothing out；condensation / water droplets 是 hydrate heating 的常见 observation。

Gas / Rate / Dilution

Gas / rate 在 2020-2025 QP 中低于 titration 和 calorimetry，但一旦出现，表格分依然看 headings、units、consistent readings。

gas syringe 表格至少包括 time / s 和 volume of gas / cm³；若是 rate，通常用 initial gradient 或 volume/time 比较。

gas identity 必须有 test result：H2 pops with lighted splint；O2 relights glowing splint；CO2 turns limewater milky。

dilution-linked titration 必须写清楚 diluted sample 与 original sample 的关系，例如 25.0 cm³ made up to 250 cm³ gives a factor of 10。

Qualitative Analysis: 写 Observation 而不是直接猜 Ion

写 colour change、precipitate colour、solubility in excess、gas evolved、gas test result、no change。

多阶段试剂必须分阶段写：after adding reagent / in excess / on heating / on standing。

空白不是 no change。没有现象时写 no visible change / no precipitate / no reaction。

自选 reagent 时必须具体：aqueous sodium hydroxide, aqueous ammonia, acidified silver nitrate, barium chloride/nitrate plus acid, dilute nitric acid/hydrochloric acid。

Qualitative Observation Bank

Test	Target	MS-ready observation	Exam note
NaOH(aq)	Cu²⁺	blue precipitate, insoluble in excess	若加热另有 NH4⁺，写 gas turns damp red litmus blue。
NaOH(aq)	Fe²⁺	green precipitate, insoluble; may turn brown on standing	standing 后颜色变化常单独给分。
NaOH(aq)	Fe³⁺	red-brown / brown / rust precipitate, insoluble in excess	Fe(OH)3 ionic equation 常考。
NaOH(aq)	Al³⁺	white precipitate, soluble in excess	与 Zn²⁺ 需结合 NH3 区分。
NaOH(aq)	Zn²⁺	white precipitate, soluble in excess	NH3 中也 soluble in excess。
NH3(aq)	Cu²⁺	pale blue precipitate, soluble in excess to deep blue solution	deep blue solution 是关键。
NH3(aq)	Zn²⁺	white precipitate, soluble in excess	若 NaOH / NH3 都 soluble，常指 Zn²⁺。
NH3(aq)	Al³⁺ / Mg²⁺	white precipitate, insoluble in excess NH3	Al³⁺ 在 NaOH excess soluble；Mg²⁺ 在 NaOH/NH3 通常 insoluble。
Ba²⁺ + acid	SO4²⁻	white precipitate, insoluble in hydrochloric / nitric acid	必须写 acid 后 insoluble / no change。
acid + limewater	CO3²⁻	effervescence; gas gives white precipitate / turns limewater milky	只写 effervescence 不一定拿满。
AgNO3 + NH3	Cl⁻ / Br⁻ / I⁻	white / cream / yellow precipitate; then solubility in ammonia	自选 reagent 时写 acidified silver nitrate。
NaOH + Al + warm	NO3⁻	ammonia evolved; damp red litmus turns blue	要写 warm / heat 与 Al。
KI + starch	oxidising agent	brown / yellow-brown iodine; starch turns dark blue / blue-black / black	颜色 + starch result 是两个 observation。
acidified KMnO4	reducing agent	purple decolourised / turns colourless	若 no reaction，写 no change / remains purple。
H2O2 + catalyst	O2	effervescence; gas relights glowing splint	不要只写 gas produced。
metal + acid	H2	effervescence; gas pops with lighted splint	pop test 是 H2 evidence。

Ionic Equations 常考模板

Context	Equation / half-equation	Why it scores
Acid + Mg / metal	Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g)	H2 pops with lighted splint.
Fe(III) + hydroxide	Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s)	red-brown / brown ppt.
Ammonium + hydroxide	NH₄⁺(aq) + OH⁻(aq) → NH₃(g) + H₂O(l)	damp red litmus turns blue.
Zn(II) + hydroxide	Zn²⁺(aq) + 2OH⁻(aq) → Zn(OH)₂(s)	white ppt, soluble in excess alkali.
Manganate(VII) redox	MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O	acid is often needed because H⁺ appears in equation.
Iodide oxidation	2I⁻ → I₂ + 2e⁻	iodine gives brown solution; starch blue-black.
Fe(III) reduction	Fe³⁺ + e⁻ → Fe²⁺	Fe³⁺ can act as oxidising agent.

Evaluation / Error Analysis

Issue	MS-ready consequence	Better answer / improvement	Sources
Heat loss	The temperature change / energy released is lower than the true value.	Use lid / insulation; take maximum temperature quickly; repeat and average if method allows.	s25/37; s25/33; s23/35; +4 older hits
Low concentration / small ΔT	ΔT will be lower, so percentage uncertainty/error is greater; slower reaction may allow more time for heat loss.	不要只写 less accurate；必须连接到 lower ΔT / percentage error / heat loss。	s25/37; s25/33; s23/35; +4 older hits
Excess acid / reagent	Student is not correct because the acid is in excess / not the limiting reagent, so exact volume is not important.	若 equation contains H+, quote H+ needed and compare moles if asked.	s25/32; s25/31; m25/33; +3 older hits
Spitting / frothing on heating	Loss of solid would make mass of residue / mass loss unreliable.	Use a lid; heat gently at first; heat to constant mass.	w25/31; w25/38
Incomplete drying / decomposition	Water lost too low or residue mass too high; hydrate number becomes too low. If substance decomposes, residue mass no longer represents anhydrous salt.	Use repeated heating/cooling/weighing; stop if decomposition is known from syllabus/question.	w25/31; w25/38

Practical Technique Tips

Skill	Action	Why it matters in MS
Burette reading	Read the bottom of the meniscus at eye level.	Avoid parallax error; accurate readings should end in 0 or 5 at 0.05 cm³ precision.
Burette setup	Fill the jet and remove air bubbles before starting.	An air bubble in the jet makes delivered volume unreliable.
Titration endpoint	Use rough titre to locate the endpoint; near the endpoint add dropwise while swirling.	For manganate(VII), stop at a permanent pale pink colour; do not overshoot.
Pipette	Rinse with the solution to be transferred; let the fixed volume drain naturally.	Do not blow out the final drop unless the apparatus instructions say so.
Volumetric flask	Make up to the calibration mark and shake / invert thoroughly.	Dilution only scores if the final volume and dilution factor are used correctly.
Calorimetry	Use lid / insulation, stir, and record maximum or minimum temperature promptly.	The main evaluation language is heat loss and its effect on ΔT / percentage error.
Heating solids	Heat gently first, then strongly if safe; cool before weighing; repeat heat-cool-weigh.	Second heating checks constant mass and reduces error from incomplete water loss.
Qualitative analysis	Use small portions, add excess when instructed, and record no change explicitly.	Write observations by stage instead of jumping straight to ion identity.

Final 5-Minute Checklist

Moment	Checklist
Before writing	Read all questions; mark which FA solutions must be kept; prepare results tables before starting measurements.
During titration	Rough first; accurate readings to 0.05 cm³; keep swirling; near endpoint add dropwise; permanent pale pink / stated endpoint must persist.
Before calculation	Select concordant titres only; mean to 2 d.p.; carry all values through with units.
For qualitative	Write observations by stage: after adding reagent, in excess, on heating, on standing; write no change when nothing happens.
For final answer	Use 3-4 s.f. unless measured values force otherwise; include sign and unit for enthalpy; use ion formulae for identities.

What Changed from the Previous Draft

原稿中的 “2009-2025 approximate frequency” 改为 2020-2025 官方 QP/MS 的 69 套证据口径。

保留原稿的滴定、仪器精度、定性分析 observation bank；新增真实 MS 高频规则、source index、error/evaluation 语言。

将 gas/rate 降为次优先，把 mass/heating/hydrate 提到 Q1/Q2 高频模块；这是近年 P3 的实际变化。

将 qualitative analysis 从“试剂知识表”改为“MS 给分语言表”：现象、过量、加热、无变化、气体检验必须分开写。