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Edexcel IAL Chemistry Unit 3 / WCH13 实验卷解题包

面向明天课堂：把 WCH13 的高频 MS 表述、Pearson CP1-CP8 实验技能、数据处理公式和观察现象整理成可以上课、复习和打印的版本。

MS 统计：23 份 QP 核对：23 份 Latest local paper：wch13-01a-rms-20260305 Exam：1 h 20 min / 50 marks
课堂路线 高频考点 计算专题

考试定位：Unit 3 是 WCH13/01 written practical paper。Pearson specification 明确它考查 Units 1 和 2 中发展出来的实验程序、实验技术、数据处理和评价能力；考试会包含 short-open、open-response 和 calculation questions，并至少有 6 marks 的 Level 2 mathematics。

答题原则：先写观察、原始数据、仪器选择、控制变量，再写结论。Edexcel MS 经常把分拆给 “做了什么” 和 “为什么这样做”。

80 分钟课堂路线

  1. 0-8 minPaper rules

    50 marks, 1 h 20 min. The paper rewards practical decisions and clean data handling, not long theory essays.

  2. 8-25 minTitration core

    Glassware purpose, rinsing rules, concordant titres, c = n/V.

  3. 25-40 minCalculation spine

    Gas volume, enthalpy, percentage uncertainty, percentage yield, significant figures.

  4. 40-55 minObservation memory

    Flame tests, anions, gases, metal hydroxides, organic functional-group tests.

  5. 55-70 minOrganic practicals

    Halogenoalkane hydrolysis, reflux/distillation, separating funnel, drying, purity.

  6. 70-80 minExam drill

    One data question and one method-improvement question under timed conditions.

Highest-Frequency First: MS/QP Practical Focus

Frequency = 本地 WCH13 MS 命中次数 / 23。Typical marks 是按题型常见分值区间整理，用来指导上课优先级，不是某一份卷子的固定分值。

FrequencyTypical marksSpec / CPPractical pointFull-mark answer movesRepresentative sources
100%
23/23		3-8Maths in practical contextQuantitative calculations and significant figures

Trap: The last mark is often lost by using cm3 directly in mol dm-3 equations.

  1. Keep units through the calculation, especially cm3 to dm3.
  2. Use apparatus precision when quoting raw data.
  3. Quote final answers to a suitable number of significant figures.
  4. Percentage uncertainty = absolute uncertainty / measured value x 100.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815
96%
22/23		5-12CP6 / CP7Organic preparation and purification

Trap: Reflux and distillation have different purposes; do not swap the explanations.

  1. Reflux prevents loss of volatile reactants or products while heating.
  2. Distillation separates a volatile product as it forms, or separates by boiling temperature.
  3. A separating funnel separates immiscible organic and aqueous layers.
  4. Dry the organic layer with an anhydrous salt before measuring boiling point or yield.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815
96%
22/23		3-7CP5Rates and halogenoalkane hydrolysis

Trap: Fastest precipitate does not mean greatest amount; it means highest rate under the same conditions.

  1. Use time, 1/time or initial gradient to compare rates.
  2. Keep concentration, volume and temperature controlled unless they are the variable.
  3. For halogenoalkane hydrolysis, faster precipitate formation means faster hydrolysis.
  4. Explain C-I > C-Br > C-Cl reactivity using decreasing C-X bond enthalpy.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815
96%
22/23		4-10CP3 / CP4Titration and standard solution

Trap: Do not average every trial if one titre is rough or non-concordant.

  1. Use a pipette for the fixed volume and a burette for the variable volume.
  2. Rinse the burette with the solution it will contain; rinse the pipette with the solution it will deliver.
  3. Record initial and final burette readings, then calculate titre.
  4. Repeat until concordant titres are obtained; calculate the mean from concordant titres only.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815
91%
21/23		5-12CP8Qualitative analysis: inorganic ions and gases

Trap: Conclusion-only answers are weak; the mark scheme usually rewards observations.

  1. Write observations first: colour, precipitate, gas and solubility in excess.
  2. For anions, acidify where required before adding the test reagent.
  3. For gases, give the test result, not just the gas name.
  4. Then give the ion conclusion using correct formulae and charges.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815
83%
19/23		4-10Units 1-2 practical observationsOrganic tests and observations

Trap: Name the colour change, not only the reagent.

  1. Alkene: bromine water changes orange/brown to colourless.
  2. Primary or secondary alcohol: acidified dichromate(VI) changes orange to green on oxidation.
  3. Aldehyde: Fehling's or Benedict's changes from blue solution to brick-red precipitate.
  4. Carboxylic acid: effervescence with carbonate or hydrogencarbonate; test CO2 if required.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815; wch13-01-rms-20240307

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815; wch13-01-rms-20240307
78%
18/23		3-7CP1Molar volume and gas collection

Trap: Connect the bung immediately; gas lost before sealing lowers the measured volume.

  1. Measure gas volume with a gas syringe or suitable gas collection method.
  2. Calculate amount of limiting reagent from mass or concentration.
  3. Molar volume = volume of gas / amount of gas.
  4. Gas leaks, dissolving gas or delayed bung fitting cause a lower measured volume.

Representative sources: wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815; wch13-01-rms-20240307

wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20260122; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815; wch13-01-rms-20240307
65%
15/23		4-9CP2Calorimetry, Hess cycle and enthalpy

Trap: Do not mix up q for the solution with DeltaH per mole of limiting reagent.

  1. Measure initial and maximum or minimum temperature, then calculate temperature change.
  2. Use q = mcDeltaT, then convert J to kJ if calculating DeltaH.
  3. State the sign of DeltaH from temperature rise or fall.
  4. Link heat loss to a smaller measured temperature change and smaller calculated energy change.

Representative sources: wch13-01a-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250116; wch13-01-rms-20240815; wch13-01-rms-20240307; wch13-01-rms-20230302; wch13-01-rms-20220818

wch13-01a-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250116; wch13-01-rms-20240815; wch13-01-rms-20240307; wch13-01-rms-20230302; wch13-01-rms-20220818
61%
14/23		3-7Data processingGraphs, gradients and anomalous results

Trap: A vague statement like 'it is wrong' does not explain an anomalous point.

  1. Choose sensible scales and label both axes with quantity and unit.
  2. Plot points accurately and draw an appropriate best-fit line or curve.
  3. Use a large triangle to calculate a gradient.
  4. Identify anomalous points by comparing them with the trend, not by preference.

Representative sources: wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250116; wch13-01-rms-20240815; wch13-01-rms-20240307; wch13-01-rms-20240118

wch13-01a-rms-20260305; wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250116; wch13-01-rms-20240815; wch13-01-rms-20240307; wch13-01-rms-20240118
57%
13/23		2-6Planning and evaluationRisk, variables and method improvement

Trap: Generic safety words rarely score unless linked to the chemical or procedure.

  1. State the specific hazard and matching precaution.
  2. Identify variables that must be controlled to make the comparison valid.
  3. Repeat measurements and calculate a mean to reduce random error.
  4. Improve apparatus by choosing higher resolution or reducing heat/gas loss where relevant.

Representative sources: wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815; wch13-01-rms-20240307

wch13-01-rms-20260305; wch13-01a-rms-20260122; wch13-01-rms-20250814; wch13-01-rms-20250306; wch13-01-rms-20250116; wch13-01r-rms-20240815; wch13-01-rms-20240815; wch13-01-rms-20240307

Core Practicals 1-8: 上课卡片

Pearson 官方 Lab Book 的 Paper 3 practical skills 对应 CP1-CP8；本页只做 Unit 3，不混入 Unit 6 的 A2 practical skills。

CP1 | Molar volume and gas collection: 18 MS hits

Measurement of the molar volume of a gas

Gas syringe, limiting reagent, volume of gas and leaks.

  1. Set up gas collection before adding solid.
  2. Use stoichiometry to convert mass or concentration to moles.
  3. Explain low volume using gas leakage, gas dissolving, or delayed sealing.
CP2 | Calorimetry, Hess cycle and enthalpy: 15 MS hits

Determination of enthalpy change using Hess's Law

Temperature change, q = mcDeltaT, Hess cycle and heat loss.

  1. Use maximum or minimum temperature, not just final reading.
  2. Convert J to kJ and divide by amount in moles.
  3. Explain heat loss directionally.
CP3 | Titration and standard solution: 22 MS hits / Quantitative calculations and significant figures: 23 MS hits

Finding the concentration of hydrochloric acid

Acid-base titration with pipette, burette, indicator and concordant titres.

  1. Use correct glassware purpose: pipette fixed, burette variable.
  2. Rinse with the solution the apparatus will contain.
  3. Mean only concordant titres.
CP4 | Titration and standard solution: 22 MS hits / Quantitative calculations and significant figures: 23 MS hits

Standard solution from solid acid and titration with sodium hydroxide

Weighing by difference, volumetric flask, dilution and titration.

  1. Transfer all solid and wash residues into the volumetric flask.
  2. Make up to the mark at eye level and invert to mix.
  3. Use c = n / V after converting cm3 to dm3.
CP5 | Rates and halogenoalkane hydrolysis: 22 MS hits

Rates of hydrolysis of halogenoalkanes

Ethanolic silver nitrate, precipitate timing and C-X bond enthalpy.

  1. Use the same volume and temperature for each halogenoalkane.
  2. Start timing when the halogenoalkane is added.
  3. White/cream/yellow precipitates indicate Cl-/Br-/I- formation.
CP6 | Organic preparation and purification: 22 MS hits

Chlorination of 2-methylpropan-2-ol

Organic preparation, separating funnel, drying and distillation.

  1. Vent the separating funnel during shaking.
  2. Remove aqueous impurities, then dry the organic layer.
  3. Use boiling temperature or yield to evaluate product quality.
CP7 | Organic preparation and purification: 22 MS hits / Organic tests and observations: 19 MS hits

Oxidation of propan-1-ol

Distillation for aldehyde; reflux for carboxylic acid.

  1. Distil propanal as it forms to reduce further oxidation.
  2. Reflux to oxidise further to propanoic acid.
  3. Dichromate(VI) changes orange to green.
CP8 | Qualitative analysis: inorganic ions and gases: 21 MS hits / Organic tests and observations: 19 MS hits

Analysis of inorganic and organic unknowns

Cation, anion, gas and functional-group observations.

  1. Record observation before conclusion.
  2. Use excess reagent behaviour when asked.
  3. State the confirmatory gas test result.

Calculation Topic Table / 计算专题

这部分适合直接给学生做板书：公式本身不难，Unit 3 的扣分点通常是单位、有效数字、方向性解释和把 q 与 DeltaH 混在一起。

TypeTemplateExam handling
Concentrationc = n / VV must be in dm3. 25.0 cm3 = 0.0250 dm3.
Amount from massn = m / MrUse the limiting reagent if a yield or enthalpy per mole is required.
Gas volumemolar volume = volume / amountKeep volume units consistent; gas loss gives a lower value.
Calorimetryq = mcDeltaTm is often the mass of solution; convert J to kJ before DeltaH.
Enthalpy per moleDeltaH = -q / nUse sign from temperature change and reaction direction.
Percentage uncertaintyabsolute uncertainty / measured value x 100For two burette readings, add the uncertainty from both readings if required.
Percentage yieldactual yield / theoretical yield x 100Theoretical yield comes from stoichiometry.
Rate comparisonrate proportional to 1 / time or gradientOnly compare if all other variables are controlled.

Observation and Test Bank / 现象库

TestTargetObservation to writeExam note
Flame testNa+ / K+ / Li+ / Ca2+ / Cu2+yellow / lilac / crimson / brick-red / blue-greenClean wire with concentrated HCl; use a non-luminous flame.
Carbonatedilute acid then limewatereffervescence; CO2 turns limewater milkyDo not stop at bubbles only.
Sulfateacidified Ba2+ solutionwhite precipitate of BaSO4Acidify to remove carbonate interference.
Halideacidified AgNO3 then NH3white / cream / yellow precipitate; different solubility in NH3Write precipitate colour before conclusion.
Ammoniumwarm with NaOHammonia turns damp red litmus blueNeeds warming and gas test result.
Metal cationsNaOH(aq) or NH3(aq)Cu2+ blue, Fe2+ green, Fe3+ brown precipitateState solubility in excess if asked.
Alkenebromine waterorange/brown to colourlessThe colour change is the observation.
Alcohol oxidationacidified K2Cr2O7orange to greenDistil for aldehyde; reflux for carboxylic acid.
Carboxylic acidcarbonate or hydrogencarbonateeffervescence; CO2 test if neededName the gas test for full observation.
AldehydeFehling's or Benedict'sblue solution to brick-red precipitateUse this to distinguish aldehyde from ketone.

Full-Mark Phrase Bank / 满分表达

More reliable

Repeat and calculate a mean; discard anomalous results only if justified by the trend.

More accurate titre

Use a pipette and burette; read the meniscus at eye level; use concordant titres.

Reduce heat loss

Use a lid, insulation, smaller time delay, or extrapolate a cooling curve where relevant.

Reduce gas loss

Fit the bung immediately and check the apparatus is airtight before starting.

Improve purity

Wash, separate, dry with an anhydrous salt, then redistil or check boiling temperature.

Control variables

Keep concentration, volume, temperature, surface area or mass constant according to the independent variable.

Sources and Teaching Basis

Pearson official specification

Unit 3 is WCH13/01, a written practical paper covering skills developed in Units 1 and 2.

Pearson Lab Book sample

Used to check CP1-CP8 sequence and the Paper 3 practical-skill framing.

Local Chemrevise mapping

Used as a teaching route map between Pearson CP1-CP8 and practical-guide pages.

Local SME practical PDFs

Used as a secondary checklist for physical, inorganic and organic core practical coverage.

Local WCH13 QP/MS archive

Used for frequency counts and representative source IDs.

版权处理：公开 Pearson 资料和本地收集资料只用于核对 scope、实验顺序和教学覆盖面；网页正文是按真题 MS/QP 统计和课堂使用需求重新组织的复习材料，不整段搬运原资料。