Edexcel AS Chemistry Colour / Observation Reference 颜色与现象速查
WCH11 / WCH12 / WCH13 常见颜色、沉淀、指示剂、气体与有机分析观察。
依据 Pearson IAL Chemistry specification、官方 Student Book 1 / Lab Book 体系、本地保存的 2019-2026 WCH11-13 QP/MS 与当前 Unit 3 分析页整理。考试作答优先写 MS 接受的观察词，如 precipitate / fumes / colourless / decolourised。
| Area | Substance / test | Colour / observation wording | Exam use / source tags |
|---|---|---|---|
| Group 7 | Cl2, Br2, I2 at room temperature |
Cl2pale green gas
Br2(l)red-brown liquid
Br2(g) / Br2(aq)brown vapourorange-brown solution
I2(s)grey-black solid
I2(g)purple vapour
|
Spec 8CTopic 8C |
| Group 7 / organic | Bromine water / Br2(aq) with C=C |
Positive C=C testyellow / orange / brown→colourless
MS wording“decolourised” is accepted; do not write “red” alone.
|
Spec 5.5WCH11 MSWCH13 MS |
| Group 7 | Iodine in aqueous / organic solvent |
I2(aq)brown
I2 in cyclohexane / organic layerpurple / violet
I- solutioncolourless
|
Spec 8CWCH12 MS |
| Halide test | AgNO3 acidified with dilute HNO3, then NH3 |
Cl- / AgClwhite precipitatesoluble in dilute NH3
Br- / AgBrcream / off-white precipitatesoluble in concentrated NH3
I- / AgIpale yellow / yellow precipitateinsoluble in NH3
|
Spec 8C / 10.10WCH13 MS |
| Halides + conc H2SO4 | NaCl / NaBr / NaI with concentrated sulfuric acid |
Cl-misty / steamy white fumes of HCl
Br-orange-brown / brown Br2 fumes
I-purple iodine vapourblack iodine solidyellow sulfur
|
Spec 8CWCH12 MS |
| Alkene oxidation | Acidified / alkaline potassium manganate(VII) |
Acidified KMnO4purple / pink→colourless
Alkaline KMnO4purple→green
Exam useAccepted as a C=C test when the reagent is specified.
|
Spec 5.4WCH11 MS |
| Alcohol oxidation | Acidified K2Cr2O7 / Cr2O7 2- |
Positive oxidationorange dichromate(VI)→green Cr3+
Negative resultremains orangeno reaction
|
Spec 10.18Topic 10CWCH13 MS |
| Alcohol test | PCl5 / phosphorus(V) chloride |
HCl fumesmisty / steamy / dense white fumes
Litmusblue litmus→red
With NH3white smoke
|
Spec 10.17Topic 10CWCH12/13 MS |
| Carbonyl / aldehyde | Fehling’s / Benedict’s; Tollens’; Brady’s / 2,4-DNPH |
Fehling’s / Benedict’s + aldehydeblue solution→red / brick-red precipitate
Tollens’ + aldehydesilver mirroror grey-black precipitate
2,4-DNPH + carbonylyellow / orange / red precipitate
|
Spec 10.18WCH13 MS |
| Carbonate / CO2 | Carbonate or hydrogencarbonate + acid; limewater |
Carbonate + acideffervescence / bubbles / fizzing
CO2 + limewatercloudy / milkyfromwhite CaCO3 precipitate
|
Topic 8BWCH13 MS |
| Sulfate | Acidified BaCl2 / Ba(NO3)2 |
SO4 2-white BaSO4 precipitate
Before Ba2+ reagentacidify first to remove carbonate interference
|
Topic 8BWCH13 MS |
| Ammonium | NH4+ warmed with NaOH(aq) |
NH3 gasdamp red litmus→blue
NH3 + HClwhite smoke
|
Topic 8BWCH13 MS |
| Flame tests | Li+, Na+, K+, Ca2+, Ba2+, Cu2+, Mg2+ |
Li+crimson-red
Na+yellow / orange-yellow
K+lilac / mauve
Ca2+orange-red / brick-red
Ba2+apple green
Cu2+blue-green
Mg2+no colour
|
Topic 8BWCH12/13 MS |
| Cation precipitates | NaOH(aq) / NH3(aq) with common AS qualitative ions |
Cu2+ + OH- / NH3blue precipitateexcess NH3:deep blue solution
Fe2+ + OH-green precipitate
Fe3+ + OH-brown precipitate
Al3+ / Mg2+ / many Group 2 ionswhite precipitatestate solubility in excess only when asked
|
WCH13 practical MSLab Book |
| Indicators | Methyl orange, phenolphthalein, litmus |
Methyl orangered in acidorange at endpointyellow in alkali
Phenolphthaleincolourless in acid/neutralpink in alkali
Litmusred in acidblue in alkali
|
Spec 8.20WCH12 MS |
| Water test | Anhydrous CuSO4 / cobalt(II) chloride paper |
Anhydrous CuSO4white→blue
Cobalt(II) chloride paperblue→pink
|
WCH13 MSpractical observation |
| Equilibrium | NO2 ⇌ N2O4 demonstration |
NO2brown
N2O4colourless
Mixturedarker brown = more NO2
|
Spec 8D suggested practicalWCH12 MS |