Principles Related to Practical Chemistry Formula Sheet — JEE Main Chemistry

Every key Principles Related to Practical Chemistry formula, definition and theorem for JEE Main Chemistry in one place — with common examiner traps and worked examples. Free to read; blurt from memory, then check your gaps.

Syllabus — topics coveredNTA · 12 sub-topics

Detection of extra elements (N, S, halogens) in organic compounds
Detection of functional groups: hydroxyl, carbonyl, carboxyl, amino
Preparation of inorganic compounds: Mohr's salt, potash alum
Preparation of organic compounds: Acetanilide, p-nitroacetanilide, aniline yellow, iodoform
Titrimetric exercises - acids, bases and indicators
Titrations: oxalic acid vs KMnO4, Mohr's salt vs KMnO4
Qualitative salt analysis - Cations: Pb2+, Cu2+, Al3+, Fe3+, Zn2+, Ni2+, Ca2+, Ba2+, Mg2+, NH4+
Qualitative salt analysis - Anions: CO3 2-, S2-, SO4 2-, NO3-, NO2-, Cl-, Br-, I-
Enthalpy of solution of CuSO4
Enthalpy of neutralization of strong acid and strong base
Preparation of lyophilic and lyophobic sols
Kinetic study of iodide ions reaction with hydrogen peroxide

Cation Analysis I — The Systematic Group Scheme (Groups 0–III)

Systematic cation analysis: Cations are sorted into

analytical groups

, each precipitated by a

group reagent

chosen so it drops only that group. The trick is controlling the precipitating-ion concentration with the

common-ion effect

(

K_{s p}

), so the least-soluble salts come down first.

Group	Cations	Group reagent → result
0	$N H_{4}^{+}$	NaOH + heat → $N H_{3}$ gas (no reagent)
I	$P b^{2 +}$	dil. HCl → white $PbC l_{2}$ (sol. in hot water)
II	$C u^{2 +}, P b^{2 +}, C d^{2 +}$	$H_{2} S$ /dil. HCl → black CuS, yellow CdS
III	$F e^{3 +}, A l^{3 +}, C r^{3 +}$	$N H_{4} Cl + N H_{4} OH$ → $Fe (OH)_{3}$ brown, $Al (OH)_{3}$ white

Groups 0 to III

▸ $Group 0$ — $N H_{4}^{+}$ : no reagent; NaOH $+$ heat $\to$ $N H_{3}$ gas.
▸ $Group I$ — $P b^{2 +}$ : dil. HCl $\to$ white $PbC l_{2}$ (dissolves in hot water).
▸ $Group II$ — $C u^{2 +}$ , $C d^{2 +}$ : $H_{2} S$ in dil. HCl $\to$ black CuS, yellow CdS.
▸ $Group III$ — $F e^{3 +}$ , $A l^{3 +}$ , $C r^{3 +}$ : $N H_{4} Cl + N H_{4} OH \to$ hydroxides.

★ Remember · Group II vs Group IV — the common-ion trick

Both use

H_{2} S

. In

Group II

the acidic medium (dil. HCl) keeps

[S^{2 -}]

low

(common-ion

H^{+}

suppresses ionisation), so only the very-insoluble sulphides drop. In

Group IV

the ammoniacal medium makes

[S^{2 -}]

high

, precipitating the rest.

🎯 Exam · NH₄Cl before NH₄OH in Group III

N H_{4} Cl

is added

before

N H_{4} OH

so the common-ion

N H_{4}^{+}

keeps

[O H^{-}]

low — only the least-soluble hydroxides (

Fe (OH)_{3}

Al (OH)_{3}

) precipitate, while Group IV–VI hydroxides stay in solution.

⚠️ Watch out · Never skip ahead

Always remove each group completely before testing the next. A cation left from an earlier group can precipitate with a later reagent and give a

false positive

— the whole scheme depends on order.

🚫 Examiner Trap · Examiner traps

(1) Follow the group order STRICTLY — never test a later group before fully removing earlier ones (carry-over gives false positives). (2) Group II uses

H_{2}

S in DILUTE HCl (low

[S^{2 -}]

, common-ion) so only the LEAST-soluble sulphides drop; Group IV raises

[S^{2 -}]

in N

H_{4}

OH. (3) Group I is dil. HCl (white PbC

l_{2}

/AgCl/H

g_{2} C l_{2}

). (4) Group 0 (NH

_{4}^{+}

) needs no reagent — NaOH

+

heat liberates N

H_{3}

Cation Analysis II — Groups IV–VI, Confirmatory & Flame Tests

Group	Cations	Group reagent → result
IV	$C o^{2 +}, N i^{2 +}, M n^{2 +}, Z n^{2 +}$	$H_{2} S$ / $N H_{4} OH$ → black NiS, white ZnS, buff MnS
V	$B a^{2 +}, S r^{2 +}, C a^{2 +}$	$(N H_{4})_{2} C O_{3}$ + $N H_{4} OH$ → white carbonates
VI	$M g^{2 +}$	no group reagent; $(N H_{4})_{2} HP O_{4}$ → white $Mg (N H_{4}) P O_{4}$

Groups IV to VI

▸ $Group IV$ — $N i^{2 +}$ , $C o^{2 +}$ , $M n^{2 +}$ , $Z n^{2 +}$ : $H_{2} S$ in $N H_{4} OH$ $\to$ black NiS, white ZnS, buff MnS.
▸ $Group V$ — $B a^{2 +}$ , $S r^{2 +}$ , $C a^{2 +}$ : $(N H_{4})_{2} C O_{3} \to$ white carbonates.
▸ $Group VI$ — $M g^{2 +}$ : no group reagent; $(N H_{4})_{2} HP O_{4} \to$ white $Mg (N H_{4}) P O_{4}$ .

🎯 Exam · Confirmatory tests to know

C u^{2 +}

N H_{4} OH \to

deep blue,

K_{4} [Fe (CN)_{6}] \to

chocolate.

F e^{3 +}

: KSCN

\to

blood red.

P b^{2 +}

: KI

\to

yellow.

N i^{2 +}

: DMG

\to

rosy red.

Z n^{2 +}

K_{4} [Fe (CN)_{6}] \to

bluish white.

The other syllabus cations

▸ $A l^{3 +}$ : gelatinous white $Al (OH)_{3}$ ; with blue litmus it gives a $blue lake$ .
▸ $C a^{2 +}$ : ammonium oxalate gives white $Ca C_{2} O_{4}$ .
▸ $B a^{2 +}$ : $K_{2} Cr O_{4}$ gives yellow $BaCr O_{4}$ .
▸ $N H_{4}^{+}$ : Nessler's reagent gives a brown precipitate (iodide of Millon's base).
▸The syllabus lists 10 cations: $P b^{2 +}$ , $C u^{2 +}$ , $A l^{3 +}$ , $F e^{3 +}$ , $Z n^{2 +}$ , $N i^{2 +}$ , $C a^{2 +}$ , $B a^{2 +}$ , $M g^{2 +}$ , $N H_{4}^{+}$ . Cd, Cr, Co, Mn and Sr appear in the group tables only to complete the scheme.

Ion	Flame colour
Na	golden yellow
K	violet / lilac
Ca	brick red
Ba	apple green
Sr	crimson
Cu	blue-green

★ Remember · Group reagent finds the group, confirmatory finds the ion

The group reagent only tells you which

group

a cation is in. A specific

confirmatory

reaction (or flame colour) is what identifies the exact ion — always note both the colour and the form of the precipitate.

🚫 Examiner Trap · Examiner traps

(1) The group reagent only PRECIPITATES the group; the CONFIRMATORY test pins the exact ion — don't stop at the precipitate. (2) Read flame colours carefully: Na golden-yellow, K lilac (view through blue glass to mask Na), Ca brick-red, Ba apple-green, Sr crimson, Cu blue-green. (3) M

g^{2 +}

(Group VI) has NO group reagent. (4) DMG (N

i^{2 +}

rosy-red) and

K_{4} [F e (CN)_{6}

] (C

u^{2 +}

chocolate / F

e^{3 +}

Prussian-blue) are the classic confirmations.

Anion Analysis — Acid Groups & Confirmatory Tests

Anion	Test / observation
$C O_{3}^{2 -}$	brisk effervescence $C O_{2}$ — lime water milky
$S^{2 -}$	$H_{2} S$ rotten-egg — lead-acetate paper black
$S O_{3}^{2 -}$	$S O_{2}$ pungent — acidified $K_{2} C r_{2} O_{7}$ turns green
$N O_{2}^{-}$	brown $N O_{2}$ fumes
$C l^{-}$	HCl fumes; $AgN O_{3}$ white (sol. $N H_{4} OH$ )
$B r^{-}$	reddish $B r_{2}$ ; $AgN O_{3}$ pale yellow
$I^{-}$	violet $I_{2}$ vapour; $AgN O_{3}$ yellow
$N O_{3}^{-}$	brown ring: $FeS O_{4}$ /conc. $H_{2} S O_{4}$
$S O_{4}^{2 -}$	$BaC l_{2}$ → white $BaS O_{4}$ (insol. in acid)
$P O_{4}^{3 -}$	ammonium molybdate/ $HN O_{3}$ → canary-yellow

Dilute H₂SO₄ group (gas evolved cold)

▸ $C O_{3}^{2 -}$ : brisk $C O_{2}$ effervescence — lime water turns milky.
▸ $S^{2 -}$ : $H_{2} S$ (rotten egg) — lead-acetate paper goes black.
▸ $S O_{3}^{2 -}$ : $S O_{2}$ (pungent) — acidified $K_{2} C r_{2} O_{7}$ turns green.
▸ $N O_{2}^{-}$ : brown $N O_{2}$ fumes.

🎯 Exam · Concentrated H₂SO₄ group

C l^{-} \to

HCl fumes,

AgN O_{3}

white (sol.

N H_{4} OH

B r^{-} \to

reddish

B r_{2}

AgN O_{3}

pale yellow.

I^{-} \to

violet

I_{2}

AgN O_{3}

yellow.

N O_{3}^{-} \to

the brown-ring test.

★ Remember · Sulphate & phosphate are tested in solution

S O_{4}^{2 -}

BaC l_{2} \to

white

BaS O_{4}

insoluble

in dilute acid (distinguishes it from sulphite/carbonate).

P O_{4}^{3 -}

: ammonium molybdate

/ HN O_{3}

, warmed

\to

canary-yellow precipitate. (The syllabus anion list is

C O_{3}^{2 -}

S^{2 -}

S O_{4}^{2 -}

N O_{3}^{-}

N O_{2}^{-}

C l^{-}

B r^{-}

I^{-}

. Sulphite and phosphate are not in the JEE Main 2026 syllabus.)

⚠️ Watch out · The brown-ring test

For

N O_{3}^{-}

: add freshly prepared

FeS O_{4}

, then pour conc.

H_{2} S O_{4}

slowly down the side of the tube. A brown ring of

[Fe (H_{2} O)_{5} NO]^{2 +}

forms at the junction. Do not shake — the ring needs the two-layer interface.

🚫 Examiner Trap · Examiner traps

(1) Always do the PRELIMINARY dilute-

H_{2} S O_{4}

test first — the gas evolved tells the group before any confirmatory step. (2) Brown-ring for NO

_{3}^{-}

: the ring is

[Fe (H_{2} O)_{5} NO]^{2 +}

, form it by adding conc.

H_{2} S O_{4}

SLOWLY down the side (don't mix). (3)

S O_{3}^{2 -}

gives pungent

S O_{2}

(turns

K_{2} C r_{2} O_{7}

green);

C O_{2}

is odourless (milky lime-water) — don't confuse. (4) Confirm Cl/Br/I by AgN

O_{3}

colour AND N

H_{4}

OH solubility (AgCl dissolves, AgBr partly, AgI no).

Organic Analysis — Detecting Elements & Functional Groups

Lassaigne sodium-fusion test: The compound is fused with sodium so its covalent N, S and halogen become

ionic

(

NaCN

N a_{2} S

NaX

), extracted into water as the 'sodium extract'. Each element is then identified by a colour test on that extract.

Element	Lassaigne (sodium-fusion) test
Nitrogen	$FeS O_{4}$ /conc. $H_{2} S O_{4}$ → Prussian blue $F e_{4} [Fe (CN)_{6}]_{3}$
Sulphur	lead acetate → black PbS; nitroprusside → violet
N + S	sodium thiocyanate → blood red $[Fe (SCN)]^{2 +}$
Halogen	$HN O_{3} + AgN O_{3}$ → white AgCl / pale-yellow AgBr / yellow AgI

Extra elements from the sodium extract

▸ $Nitrogen$ : $FeS O_{4}$ /conc. $H_{2} S O_{4} \to$ Prussian blue $F e_{4} [Fe (CN)_{6}]_{3}$ .
▸ $Sulphur$ : lead acetate $\to$ black PbS; nitroprusside $\to$ violet.
▸ $N and S together$ : thiocyanate $\to$ blood-red $[Fe (SCN)]^{2 +}$ .
▸ $Halogen$ : $HN O_{3} + AgN O_{3} \to$ white AgCl / pale-yellow AgBr / yellow AgI.

Group	Positive test
–OH (alcohol)	Na → H₂; ceric ammonium nitrate → red
–OH (phenol)	neutral FeCl₃ → violet; Br₂ water → white ppt
–CHO	Tollens silver mirror; Fehling red-brown
>C=O	2,4-DNP orange-red (ketone fails Tollens)
–COOH	NaHCO₃ → brisk CO₂; litmus red
–NH₂ (1°)	carbylamine (foul isocyanide)
Ar–NH₂ (1°)	diazotise at 273–278 K, then β-naphthol → orange-red azo dye
C=C / C≡C	decolourises Br₂ water & Baeyer's reagent

⚠️ Watch out · Boil off HCN & H₂S before the halogen test

If N or S is present, boil the sodium extract with dil.

HN O_{3}

first — otherwise

C N^{-}

and

S^{2 -}

would give

AgCN

A g_{2} S

precipitates and a

false halogen result

🚫 Examiner Trap · Examiner traps

(1) Lassaigne's sodium fusion converts N, S, X to ionic NaCN/N

a_{2}

S/NaX (covalent forms wouldn't test). (2)

N+S together

give blood-red [Fe(SCN)

]^{2 +}

(thiocyanate), NOT the Prussian-blue you'd get for N alone — a classic trap. (3) Halogen test needs the cyanide/sulphide BOILED off with HN

O_{3}

first (they'd mask AgX). (4) 2,4-DNP is positive for ALL

> C =

O, but Tollens/Fehling pick out the ALDEHYDE; aromatic aldehydes fail Fehling.

Titrimetric Analysis & the Physical Experiments

★ Remember · Match the indicator to the equivalence pH

N_{1} V_{1} = N_{2} V_{2}

Methyl orange

(pH 3.1–4.4) marks a strong-acid end-point;

phenolphthalein

(8.3–10) a strong-base one. SA–SB: any; WA–SB: phenolphthalein; SA–WB: methyl orange; WA–WB: no sharp end-point.

🎯 Exam · KMnO₄ — self-indicator, acidic medium only

KMn O_{4}

is its own indicator (first permanent pink = end-point). Use

dilute

H_{2} S O_{4}

— never HCl (

C l^{-}

is oxidised) or

HN O_{3}

(itself oxidising).

Mn O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O

(

n = 5

Oxalic acid

2 Mn O_{4}^{-} + 5 C_{2} O_{4}^{2 -} + 16 H^{+} \to 2 M n^{2 +} + 10 C O_{2} + 8 H_{2} O

Mohr's salt

Mn O_{4}^{-} + 5 F e^{2 +} + 8 H^{+} \to M n^{2 +} + 5 F e^{3 +} + 4 H_{2} O

💡 Tip · Warm the oxalic acid, not the Mohr's salt

Oxalic acid is warmed to 333–343 K because the reaction starts slowly; the

M n^{2 +}

it forms then catalyses it (

autocatalysis

). Mohr's salt is titrated

cold

, because warming would let air oxidise

F e^{2 +}

. Moles:

KMn O_{4} : C_{2} O_{4}^{2 -} = 2 : 5

and

KMn O_{4} : F e^{2 +} = 1 : 5

★ Remember · Equivalents & n-factors

equivalent weight

= \frac{molar mass}{n}

, normality

=

molarity

\times n

. Oxalic acid

n = 2

; Mohr's salt (

F e^{2 +}

)

n = 1

;

KMn O_{4}

n = 5

;

K_{2} C r_{2} O_{7}

n = 6

🎯 Exam · Primary vs secondary standards

primary standard

(oxalic acid,

K_{2} C r_{2} O_{7}

) is pure, stable, non-hygroscopic and of known formula, so it can be weighed directly.

Secondary

solutions (

KMn O_{4}

, NaOH, HCl) must first be standardised against a primary standard.

Syllabus experiment	Principle
Enthalpy of solution of $CuS O_{4}$	$Δ H = - \frac{( m c + W ) Δ T}{n}$ (W = water equivalent of the calorimeter, n = moles dissolved); anhydrous $CuS O_{4}$ is exothermic because it hydrates
Enthalpy of neutralisation, SA + SB	always about $- 57.1 kJ mol^{- 1}$ ( $H^{+} + O H^{-} \to H_{2} O$ ); smaller in magnitude with a weak acid or base, which must first ionise
Lyophilic and lyophobic sols	lyophilic (starch, gum, egg albumin) forms simply by warming with water; lyophobic needs chemical methods, e.g. $Fe (OH)_{3}$ sol by hydrolysing $FeC l_{3}$ in boiling water, or an $A s_{2} S_{3}$ sol
Kinetics of $I^{-} + H_{2} O_{2}$	$H_{2} O_{2} + 2 I^{-} + 2 H^{+} \to I_{2} + 2 H_{2} O$ ; time the starch-blue appearance (iodine clock, $N a_{2} S_{2} O_{3}$ delays it); rate $\propto$ [ $I^{-}$ ] at fixed $H_{2} O_{2}$

🚫 Examiner Trap · Examiner traps

(1) KMn

O_{4}

is a SELF-indicator (pink end-point) — use dilute

H_{2} S O_{4}

, NEVER HCl (Cl

^{-}

gets oxidised, false high reading) and never HN

O_{3}

(oxidising). (2) Equivalent weight

=

molar mass

/ n

-factor; get n right (

Mn O_{4}^{-}

n = 5

acidic, oxalic

n = 2

K_{2} C r_{2} O_{7}

n = 6

). (3) Primary standard must be pure, stable, non-hygroscopic (oxalic acid,

K_{2} C r_{2} O_{7}

); KMn

O_{4}

/NaOH/HCl are SECONDARY — standardise first. (4) Match indicator to titration: SA-WB

\to

methyl orange, WA-SB

\to

phenolphthalein.

Purification, Crystallisation & Chromatography

Method	Separates by
Crystallisation	different solubility in hot vs cold solvent
Sublimation	solid ⇌ vapour without melting (camphor, $N H_{4} Cl$ )
Simple distillation	liquids with a large BP gap + non-volatile impurity
Fractional distillation	liquids with close boiling points
Steam distillation	steam-volatile, water-immiscible solids (aniline)
Differential extraction	solute more soluble in an immiscible solvent

Method ↔ differing property

▸ $Crystallisation$ : different solubility hot vs cold (impurity stays in mother liquor).
▸ $Sublimation$ : solid ⇌ vapour without melting (camphor, $N H_{4} Cl$ ).
▸ $Simple distillation$ : large b.p. gap; $fractional$ : close b.p. (column).
▸ $Steam distillation$ : steam-volatile, water-immiscible ( $p = p_{1} + p_{2}$ ).

★ Remember · Distillation variants

Reduced-pressure

distillation lowers the boiling point for heat-sensitive/high-b.p. liquids (e.g. glycerol).

Differential extraction

uses a separating funnel when the solute is more soluble in an immiscible solvent.

🎯 Exam · Chromatography & the Rf value

Components separate by moving at different rates:

adsorption

(column/TLC on silica/alumina) or

partition

(paper, water = stationary phase).

R_{f} = \frac{distance moved by solute}{distance moved by solvent}

— a constant (

0 < R_{f} \leq 1

) for a given system.

⚠️ Watch out · Rf is always ≤ 1

The solute can never travel faster than the solvent front, so

R_{f}

is always between 0 and 1. A larger

R_{f}

means the component is less strongly adsorbed (more soluble in the mobile phase).

🚫 Examiner Trap · Examiner traps

(1) Choose the method by the property that DIFFERS: solubility → crystallisation, big b.p. gap → simple distillation, close b.p. → fractional, solid ⇌ vapour → sublimation, water-immiscible volatile → steam distillation. (2) Steam distillation needs a water-IMMISCIBLE, steam-volatile substance (

p = p_{1} + p_{2}

, distils below 100

^{\circ}

C). (3)

R_{f}

is always

0 < R_{f} \leq 1

and is constant for a given system. (4) Crystallisation leaves the impurity in the MOTHER LIQUOR (not the crystals).

Chemical Principles in Preparation of Compounds

Inorganic double salts

▸ $Mohr’s salt$ $FeS O_{4} \cdot (N H_{4})_{2} S O_{4} \cdot 6 H_{2} O$ — light-green; a stable $F e^{2 +}$ standard.
▸ $Potash alum$ $K_{2} S O_{4} \cdot A l_{2} (S O_{4})_{3} \cdot 24 H_{2} O$ — large octahedral crystals.
▸Both are crystallised from an $equimolar$ mixture of the two simple salts.
▸A double salt ionises $fully$ in water (all ions free); a complex keeps its coordination sphere.

Product	Reaction / principle
Acetanilide	aniline + acetic anhydride (acetylation)
p-Nitroacetanilide	acetanilide + conc. HNO₃/H₂SO₄ in the cold (nitration; the –NHCOCH₃ group directs para)
Aniline yellow (p-aminoazobenzene)	benzenediazonium chloride + aniline (azo coupling at para)
Iodoform	ethanol/acetone + I₂/NaOH (haloform)
Aspirin (not in JEE Main 2026 syllabus)	salicylic acid + acetic anhydride/H⁺ (acetylation)
Dibenzal acetone (not in JEE Main 2026 syllabus)	2 PhCHO + acetone/NaOH (cross-aldol)

★ Remember · Every prep is a named reaction

None of these is new chemistry. Acetanilide is an

acetylation

. p-Nitroacetanilide is a

nitration

of the protected amine (the acetyl group tames –N

H_{2}

and blocks meta attack). Aniline yellow is a diazonium

coupling

, and iodoform is the

haloform

reaction. Recognise the principle and the product follows.

🚫 Examiner Trap · Examiner traps

(1) A DOUBLE salt (Mohr's salt, alum) ionises COMPLETELY in water (gives all its ions, e.g. F

e^{2 +}

test positive); a COMPLEX keeps a stable coordination sphere (won't give free-ion tests). (2) Mohr's salt is a stable F

e^{2 +}

primary standard; alum gives large octahedral crystals. (3) Each syllabus organic prep rests on a named reaction: acetanilide

=

acetylation, p-nitroacetanilide

=

nitration (para), aniline yellow

=

azo coupling, iodoform

=

haloform. (4) Use equimolar mixtures and slow crystallisation for double salts.

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This Principles Related to Practical Chemistry formula sheet covers all the high-yield Chemistry formulas, definitions and theorems you need for JEE Main, across Detection of extra elements (N, S, halogens) in organic compounds, Detection of functional groups: hydroxyl, carbonyl, carboxyl, amino, Preparation of inorganic compounds: Mohr's salt, potash alum, Preparation of organic compounds: Acetanilide, p-nitroacetanilide, aniline yellow, iodoform, Titrimetric exercises - acids, bases and indicators — each shown with the key result and, where useful, a worked example.

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