Feature 03
Chemistry & Science Quick Tips
Two-minute revision cards for the topics examiners love.
Baeyer's Reagent
KMnO₄ (alkaline, cold)
Test for unsaturation (C=C, C≡C)
Observation: Purple → colourless / brown ppt
Fehling's Solution
Cu²⁺ tartrate complex
Test for aldehydes (not ketones)
Observation: Blue → brick-red precipitate
Tollens' Reagent
[Ag(NH₃)₂]⁺
Test for aldehydes
Observation: Colourless → silver mirror
Jones Reagent
H₂CrO₄ / H₂SO₄ (from K₂Cr₂O₇)
Oxidation of 1° and 2° alcohols
Observation: Orange → green
Lucas Reagent
ZnCl₂ + conc. HCl
Differentiate 1°, 2°, 3° alcohols
Observation: 3° cloudy at once, 2° 5–10 min, 1° no change at r.t.
Bromine Water
Br₂(aq)
Test for unsaturation & phenols
Observation: Orange/brown → colourless
2,4-DNPH (Brady's)
C₆H₃(NO₂)₂NHNH₂
Test for carbonyl (C=O) groups
Observation: Yellow/orange precipitate
Iodoform Test
I₂ / NaOH
CH₃CO– group or CH₃CH(OH)– group
Observation: Pale-yellow CHI₃ precipitate
Grignard Reagent
RMgX
Forms C–C bonds; alcohols from carbonyls
Observation: —
Friedel–Crafts Catalyst
AlCl₃, FeCl₃
Alkylation / acylation of benzene
Observation: —
Lindlar's Catalyst
Pd / CaCO₃ poisoned with Pb
Partial hydrogenation of alkynes → cis-alkenes
Observation: —