jee main chemistry important questions | Purification And Characterization Of Organic Compounds

Q 1 :

The Lassaigne’s extract is boiled with dilute ${HNO}_{3}$ , before testing for halogens because, [2024]

AgCN is soluble in ${HNO}_{3}$ .
Silver halides are soluble in ${HNO}_{3}$ .
${Ag}_{2} S$ is soluble in ${HNO}_{3}$ .
${Na}_{2} S$ and NaCN are decomposed by ${HNO}_{3}$ .

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(4)

If the salt contains sulphide or cyanide, then Lassaigne’s extract would contain ${Na}_{2} S$ or NaCN. In such cases, upon the addition of ${AgNO}_{3}$ in the extract, ${Ag}_{2} S$ (black precipitate) or AgCN (white residue) are obtained which interferes with the test for halides. Hence Lassaigne’s extract is boiled with dil. ${HNO}_{3}$ to decompose ${Na}_{2} S$ or NaCN.

Q 2 :

Lassaigne’s test is used for detection of: [2024]

Phosphorous and halogens only
Nitrogen, Sulphur and Phosphorous only
Nitrogen, Sulphur, Phosphorous and halogens
Nitrogen and Sulphur only

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(3)

Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by “Lassaigne’s test”.

Q 3 :

Which of the following nitrogen containing compound does not give Lassaigne’s test? [2024]

Glycine
Hydrazine
Phenyl hydrazine
Urea

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(2)

In Lassaigne's test for nitrogen, NaCN is formed in sodium fusion extract, which is then tested further. Hydrazine ( ${NH}_{2} - {NH}_{2}$ ) does not contain carbon hence NaCN cannot be formed in sodium fusion extract. So hydrazine does not give Lassaigne 's test for nitrogen.

Q 4 :

Given below are two statements: [2025]

Statement I: Nitrogen, sulphur, halogen and phosphorus present in an organic compound are detected by Lassaigne’s Test.

Statement II: The elements present in the compound are converted from covalent form into ionic form by fusing the compound with Magnesium in Lassaigne’s test.

In the light of the above statements, choose the correct answer from the options given below:

Statement I is false but Statement II is true
Both Statement I and Statement II are false
Both Statement I and Statement II are true
Statement I is true but Statement II is false

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(4)

Elements are converted from covalent to ionic form by fusion with sodium metal.

Q 5 :

Given below are two statements: [2025]

Statement I: In Lassaigne’s test, the covalent organic molecules are transformed into ionic compounds.

Statement II: The sodium fusion extract of an organic compound having N and S gives prussian blue colour with ${FeSO}_{4}$ and ${Na}_{4} [Fe {(CN)}_{6}]$ .

In the light of the above statements, choose the correct answer from the options given below:

Statement I is false but Statement II is true
Both Statement I and Statement II are false
Both Statement I and Statement II are true
Statement I is true but Statement II is false

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(4)

If an organic compound has both S and N, then its sodium fusion extract gives blood red colour during test of N.

Q 6 :

Compound that will give positive Lassaigne’s test for both nitrogen and halogen is: [2023]

${NH}_{2} OH . HCl$
${CH}_{3} {NH}_{2} . HCl$
${NH}_{4} Cl$
$N_{2} H_{4} . HCl$

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(2)

Lassaigne test for both nitrogen and halogen is given by the compound which have C, N as well as X atom in the compound.

Q 7 :

Which of the following compounds would give the following set of qualitative analysis? [2023]

(i) Fehling’s Test: Positive

(ii) Na fusion extract upon treatment with sodium nitroprusside gives a blood-red colour but not Prussian blue.

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(2)

Fehling test given by aldehyde but not aromatic aldehyde and if N and S attached with carbon atom give blood red with sodium nitroprusside gives a blood red colour but not prussian blue.

Q 8 :

Given below are two statements:

Statement I: Sulphanilic acid gives esterification test for carboxyl group.

Statement II: Sulphanilic acid gives red colour in Lassaigne’s test for extra element detection.

In the light of the above statements, choose the correct answer from the options given below: [2023]

Both Statement I and Statement II are correct
Both Statement I and Statement II are incorrect
Statement I is incorrect but Statement II is correct
Statement I is correct but Statement II is incorrect

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(3)

Sulphanilic acid has no –COOH group hence no esterification test for carboxyl group. But it has sulpher and nitrogen atom hence gives red colour in Lassigne’s test for extra element detection.

Q 9 :

Match List I with List II. [2023]

List I List II

Element Detected Reagent used/Product formed

A. Nitrogen I. ${Na}_{2} [Fe {(CN)}_{5} NO]$

B. Sulphur II. ${AgNO}_{3}$

C. Phosphorus III. ${Fe}_{4} {[Fe {(CN)}_{6}]}_{3}$

D. Halogen IV. ${({NH}_{4})}_{2} {MoO}_{4}$

Choose the correct answer from the options given below:

A–III, B–I, C–IV, D–II
A–II, B–IV, C–I, D–III
A–II, B–I, C–IV, D–III
A–IV, B–II, C–I, D–III

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(A) $‘N’ + {[Fe {(CN)}_{6}]}^{4 -} \to Blue colour$

(B) $‘S’ + Sodium nitroprusside \to Violet colour$

(C) $‘P’ + {({NH}_{4})}_{2} {MoO}_{4} \to {({NH}_{4})}_{3} {PO}_{4} . 12 {MoO}_{3} \to Yellow colour$

(D) $Halogen + {AgNO}_{3} \to AgX ppt$

Q 10 :

Given below are two statements:

Statement I: Griss–Ilosvay test is used for the detection of nitrite ion, which involves the use of sulphanilic acid and $α$ -naphthylamine reagent.

Statement II: In the above test, sulphanilic acid is diazotized by the acidified nitrite ion, which on further coupling with $α$ -naphthylamine forms an azo-dye.

In the light of the above statements, choose the correct answer from the options given below: [2026]

Both Statement I and Statement II are false
Statement I is true but Statement II is false
Both Statement I and Statement II are true
Statement I is false but Statement II is true

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(3)

Q 11 :

A sample of hydrate of barium chloride weighing 61 g was heated until all the water of hydration was removed. The dried sample weighed 52 g. The formula of the hydrated salt is: (Atomic mass of Ba = 137 amu, Cl = 35.5 amu).

${BaCl}_{2} \cdot H_{2} O$
${BaCl}_{2} \cdot 3 H_{2} O$
${BaCl}_{2} \cdot 4 H_{2} O$
${BaCl}_{2} \cdot 2 H_{2} O$

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(4)

${BaCl}_{2} \cdot {xH}_{2} O \to {BaCl}_{2} + {xH}_{2} O,$ $(137 + 2 \times 35.5 + 18 x) = (208 + 18 x) g / mole$

$\frac{208 + 18 x}{208} = \frac{61}{52},$ $52 (208 + 18 x) = 61 \times 208,$

$10816 + 936 x = 12688,$ $936 x = 1872,$ $x = 2,$

Formula is ${BaCl}_{2} \cdot 2 H_{2} O$

Q 12 :

Number of metal ions characterized by flame test among the following is ___________

$S r^{2 +}, B a^{2 +}, C a^{2 +}, C u^{2 +}, Z n^{2 +}, C o^{2 +}, F e^{2 +}, N a^{+}, K^{+}$

(6)

${Sr}^{2 +}, {Ba}^{2 +}, {Ca}^{2 +}, {Cu}^{2 +}, {Na}^{+}, K^{+}$

Q 13 :

Match List - I with List - II.

$\begin{matrix} List - I \\ (Mixture of Compounds) \end{matrix}$ $\begin{matrix} List - II \\ (Reagent used to distinguish) \end{matrix}$

A. Diethyl amine + Ethyl amine I. Bromine water

B. Acetaldehyde + Acetone II. ${CHCl}_{3} + KOH, Δ$

C. Ethanol + Phenol III. Neutral ${FeCl}_{3}$

D. Benzoic acid + Cinnamic acid IV. Ammonical silver nitrate

Choose the correct answer from the options given below: [2026]

A-IV, B-II, C-I, D-III
A-IV, B-II, C-III, D-I
A-II, B-IV, C-I, D-III
A-II, B-IV, C-III, D-I

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(4)

A: Primary amines (e.g. ethyl amine) give carbylamine reaction (reaction with ${CHCl}_{3}$ + KOH). Secondary (e.g. diethyl amine) and tertiary amines do not give this test.

B: Aldehydes (e.g. acetaldehyde) give Tollen's test (reaction with ammonical silver nitrate) and ketones (e.g. acetone do not).

C: Phenol gives white ppt. with bromine water and gives violet colour with neutral ${FeCl}_{3}$ . Ethanol does not give these tests.

D: Cinnamic acid contains a double bond. Red colour of bromine water is discharged by bromine water, hence cinnamic acid gives bromine water test and benzoic acid does not.

Q 14 :

Match List - I with List - II.

$\begin{matrix} List - I \\ (Compound) \end{matrix}$ $\begin{matrix} List - II \\ (Test) \end{matrix}$

A. [IMAGE 297] I. Hinsberg's reagent test

B. [IMAGE 298] II. Phthalein dye test

C. [IMAGE 299] III. Lucas test

D. [IMAGE 300] IV. Tollen's test

Choose the correct answer from the options given below: [2026]

A-III, B-I, C-IV, D-II
A-III, B-IV, C-I, D-II
A-I, B-III, C-II, D-IV
A-I, B-II, C-III, D-IV

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(1)

Fact based

Topic Question Set

Q 1 :

The Lassaigne’s extract is boiled with dilute ${HNO}_{3}$ , before testing for halogens because, [2024]

Q 2 :

Lassaigne’s test is used for detection of: [2024]

Q 3 :

Which of the following nitrogen containing compound does not give Lassaigne’s test? [2024]

Q 6 :

Compound that will give positive Lassaigne’s test for both nitrogen and halogen is: [2023]

Q 7 :

Which of the following compounds would give the following set of qualitative analysis? [2023]

(i) Fehling’s Test: Positive

(ii) Na fusion extract upon treatment with sodium nitroprusside gives a blood-red colour but not Prussian blue.

Q 11 :

A sample of hydrate of barium chloride weighing 61 g was heated until all the water of hydration was removed. The dried sample weighed 52 g. The formula of the hydrated salt is: (Atomic mass of Ba = 137 amu, Cl = 35.5 amu).

Q 12 :

Number of metal ions characterized by flame test among the following is ___________

$S r^{2 +}, B a^{2 +}, C a^{2 +}, C u^{2 +}, Z n^{2 +}, C o^{2 +}, F e^{2 +}, N a^{+}, K^{+}$

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	List I		List II
	Element Detected		Reagent used/Product formed
A.	Nitrogen	I.	${Na}_{2} [Fe {(CN)}_{5} NO]$
B.	Sulphur	II.	${AgNO}_{3}$
C.	Phosphorus	III.	${Fe}_{4} {[Fe {(CN)}_{6}]}_{3}$
D.	Halogen	IV.	${({NH}_{4})}_{2} {MoO}_{4}$

	$\begin{matrix} List - I \\ (Mixture of Compounds) \end{matrix}$		$\begin{matrix} List - II \\ (Reagent used to distinguish) \end{matrix}$
A.	Diethyl amine + Ethyl amine	I.	Bromine water
B.	Acetaldehyde + Acetone	II.	${CHCl}_{3} + KOH, Δ$
C.	Ethanol + Phenol	III.	Neutral ${FeCl}_{3}$
D.	Benzoic acid + Cinnamic acid	IV.	Ammonical silver nitrate

	$\begin{matrix} List - I \\ (Compound) \end{matrix}$		$\begin{matrix} List - II \\ (Test) \end{matrix}$
A.	[IMAGE 297]	I.	Hinsberg's reagent test
B.	[IMAGE 298]	II.	Phthalein dye test
C.	[IMAGE 299]	III.	Lucas test
D.	[IMAGE 300]	IV.	Tollen's test

Topic Question Set

Q 1 : The Lassaigne’s extract is boiled with dilute HNO3, before testing for halogens because, [2024]

Q 2 : Lassaigne’s test is used for detection of: [2024]

Q 3 : Which of the following nitrogen containing compound does not give Lassaigne’s test? [2024]

Q 6 : Compound that will give positive Lassaigne’s test for both nitrogen and halogen is: [2023]

Q 7 : Which of the following compounds would give the following set of qualitative analysis? [2023] (i) Fehling’s Test: Positive (ii) Na fusion extract upon treatment with sodium nitroprusside gives a blood-red colour but not Prussian blue.

Q 9 : Match List I with List II. [2023] List I List II Element Detected Reagent used/Product formed A. Nitrogen I. Na2[Fe(CN)5NO] B. Sulphur II. AgNO3 C. Phosphorus III. Fe4[Fe(CN)6]3 D. Halogen IV. (NH4)2MoO4 Choose the correct answer from the options given below:

Q 11 : A sample of hydrate of barium chloride weighing 61 g was heated until all the water of hydration was removed. The dried sample weighed 52 g. The formula of the hydrated salt is: (Atomic mass of Ba = 137 amu, Cl = 35.5 amu).

Q 12 : Number of metal ions characterized by flame test among the following is ___________ Sr2+, Ba2+, Ca2+, Cu2+, Zn2+, Co2+, Fe2+, Na+, K+

Q 14 : Match List - I with List - II. List - I(Compound) List - II(Test) A. [IMAGE 297] I. Hinsberg's reagent test B. [IMAGE 298] II. Phthalein dye test C. [IMAGE 299] III. Lucas test D. [IMAGE 300] IV. Tollen's test Choose the correct answer from the options given below: [2026]

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Q 1 :

The Lassaigne’s extract is boiled with dilute ${HNO}_{3}$ , before testing for halogens because, [2024]

Q 2 :

Lassaigne’s test is used for detection of: [2024]

Q 3 :

Which of the following nitrogen containing compound does not give Lassaigne’s test? [2024]

Q 6 :

Compound that will give positive Lassaigne’s test for both nitrogen and halogen is: [2023]

Q 7 :

Which of the following compounds would give the following set of qualitative analysis? [2023]

(i) Fehling’s Test: Positive

(ii) Na fusion extract upon treatment with sodium nitroprusside gives a blood-red colour but not Prussian blue.

Q 11 :

A sample of hydrate of barium chloride weighing 61 g was heated until all the water of hydration was removed. The dried sample weighed 52 g. The formula of the hydrated salt is: (Atomic mass of Ba = 137 amu, Cl = 35.5 amu).

Q 12 :

Number of metal ions characterized by flame test among the following is ___________

$S r^{2 +}, B a^{2 +}, C a^{2 +}, C u^{2 +}, Z n^{2 +}, C o^{2 +}, F e^{2 +}, N a^{+}, K^{+}$