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Principles Related to Practical Chemistry: one-page cheat sheet

NEET Chemistry · Unit 20 · Practical Chemistry

ScoreChemby CSJ Sir
Weightage: 1–2 questions · 4–8 marks

1 · Extra elements

Sodium fusion turns covalent N, S, X into ionic NaCN, Na $_{2}$ S, NaX.

Element	Observation
N	Prussian blue
S	purple (nitroprusside); black PbS
N + S	blood red [Fe(SCN)] $^{2 +}$
X	AgCl white; AgBr pale yellow; AgI yellow
P	canary yellow with molybdate

CuO + C is the carbon test, not part of Lassaigne's test.

2 · Functional group tests

C=C, C≡CBr

_{2}

and Baeyer's reagent decolourised

AlcoholNa gives H

_{2}

; Lucas:

3^{\circ}

at once,

2^{\circ}

in 5 min,

1^{\circ}

none

Phenolneutral FeCl

_{3}

violet; Br

_{2}

water white ppt

C=O2,4-DNP orange for both aldehydes and ketones

AldehydeTollens' mirror; Fehling's (aliphatic only)

IodoformCH

_{3}

CO– or CH

_{3}

CH(OH)–: yellow CHI

_{3}

–COOHNaHCO

_{3}

gives CO

_{2}

; phenols do not

1^{\circ}

aminecarbylamine, azo dye, Hinsberg

3 · Preparations

Mohr's saltFeSO

_{4}

+ (NH

_{4}

)

_{2}

_{4}

in dil. H $_{2}$ SO $_{4}$ (stops Fe

^{2 +}

hydrolysis); pale green, double salt

Potash alumAl scrap + KOH, then H

_{2}

_{4}

; octahedral colourless crystals

Acetanilideaniline + (CH

_{3}

CO)

_{2}

O; Zn dust stops oxidation

Nitrationp-nitroacetanilide: nitrating mixture below 288 K; para major

Aniline yellowdiazotise (273–278 K), couple with aniline

4 · Titrations

n_{1} M_{1} V_{1} = n_{2} M_{2} V_{2}

n-factorsKMnO

_{4}

(acid) 5; oxalic acid 2; Mohr's salt 1

Primary std.oxalic acid, Na

_{2}

_{3}

, Mohr's salt; not NaOH or KMnO

_{4}

Indicator	Use
phenolphthalein (8.3–10)	strong/strong; weak acid/strong base
methyl orange (3.1–4.4)	strong acid/weak base
none sharp	weak acid/weak base

5 · KMnO $_{4}$ titrations

Oxalic acidwarm to 60–70 °C; dil. H

_{2}

_{4}

; self-indicator; autocatalysed by Mn

^{2 +}

Mohr's saltin the cold; dil. H

_{2}

_{4}

Why H

_{2}

_{4}

HCl is oxidised to Cl

_{2}

; HNO

_{3}

is itself an oxidant

End pointfirst permanent light pink; read the top of the meniscus

20 mL of 0.05 M oxalic acid needs 25 mL KMnO $_{4}$ : $2 \times 0.05 \times 20 = 5 \times M \times 25$ , so $M = 0.016$ M.

6 · Anion analysis

Ion	Test
CO $_{3}^{2 -}$	dil. acid: CO $_{2}$ turns lime water milky
S $^{2 -}$	H $_{2}$ S; lead acetate black; nitroprusside purple
SO $_{3}^{2 -}$	SO $_{2}$ turns K $_{2}$ Cr $_{2}$ O $_{7}$ green
Cl $^{-}$	HCl fumes; chromyl chloride test (red CrO $_{2}$ Cl $_{2}$ )
Br $^{-}$ / I $^{-}$	brown Br $_{2}$ / violet I $_{2}$
SO $_{4}^{2 -}$	BaCl $_{2}$ : white, insoluble in HCl
NO $_{3}^{-}$	brown ring (FeSO $_{4}$ + conc. H $_{2}$ SO $_{4}$ )

7 · Cation groups

Group	Cations	Reagent
0	NH $_{4}^{+}$	NaOH; Nessler's: brown
I	Pb $^{2 +}$	dil. HCl
II	Cu $^{2 +}$ (Pb $^{2 +}$ )	H $_{2}$ S, dil. HCl
III	Fe $^{3 +}$ , Al $^{3 +}$	NH $_{4}$ OH, NH $_{4}$ Cl
IV	Zn, Ni, Co, Mn	H $_{2}$ S, NH $_{4}$ OH
V	Ba, Ca, Sr	(NH $_{4}$ ) $_{2}$ CO $_{3}$
VI	Mg $^{2 +}$	Na $_{2}$ HPO $_{4}$

ConfirmFe

^{3 +}

+ KSCN red; Ni

^{2 +}

+ DMG red; Cu

^{2 +}

+ excess NH

_{4}

OH deep blue

FlameBa apple green; Ca brick red; Sr crimson

8 · Thermochemistry & sols

Calorimeter

q = m s Δ T

;

Δ_{so l} H = q / n

Neutralisationstrong acid + strong base: about

- 57

kJ mol

^{- 1}

Lyophilicstarch, gum, albumin: stable, reversible

LyophobicFe(OH)

_{3}

(FeCl

_{3}

into boiling water), As

_{2}

_{3}

Seen in NEET 2026

BiO(OH) $⇌$ BiO $^{+}$ + OH $^{-}$ , $K = 4 \times 1 0^{- 10}$ .

x = 2 \times 1 0^{- 5}, pOH = 4.699, pH = 9.301

Seen in NEET 2024

Cu $^{2 +}$ (II), Al $^{3 +}$ (III), Co $^{2 +}$ (IV), Ba $^{2 +}$ (V), Mg $^{2 +}$ (VI): increasing group number.

Mohr's salt is made in dilute H $_{2}$ SO $_{4}$ .

Seen in NEET 2026

NaOH added to oxalic acid with phenolphthalein: colourless to pink.

Six traps to remember

Lassaigne's test converts covalent to ionic form; CuO + C is not part of it.
2,4-DNP does not separate aldehydes from ketones.
Mohr's salt needs dilute H $_{2}$ SO $_{4}$ , never HCl or HNO $_{3}$ .
n-factors: KMnO $_{4}$ 5, oxalic acid 2, Mohr's salt 1.
Co $^{2 +}$ and Ni $^{2 +}$ are Group IV, Mg $^{2 +}$ is Group VI.
Weak acid vs weak base has no sharp indicator.

Principles Related to Practical Chemistry: free one-page cheat sheet

1 · Extra elements

2 · Functional group tests

3 · Preparations

4 · Titrations

5 · KMnO4​ titrations

6 · Anion analysis

7 · Cation groups

8 · Thermochemistry & sols

Seen in NEET 2026

Seen in NEET 2024

Seen in NEET 2026

Six traps to remember

5 · KMnO $_{4}$ titrations