QBManager

PRACTICAL CHEMISTRY

286931 The Lassaigne's extract is boiled with conc. ${HNO}_{3}$ while testing for halogens. By doing so it

1 decomposes

{Na}_{2} S

and NaCN , if formed.

2 helps in the precipitation of AgCl .

3 increases the solubility product of AgCl .

4 increases the concentration of

{NO}_{3}^{-}

ions.

Explanation:

(a) Conc. ${HNO}_{3}$ decomposes NaCN and ${Na}_{2} S$ to avoid their interference.
$NaCN + {HNO}_{3} ⟶ {NaNO}_{3} + HCN ↑$
${Na}_{2} S + 2 {HNO}_{3} ⟶ 2 {NaNO}_{3} + H_{2} S ↑$

NCERT | Page-354 / N-284 | 2011

PRACTICAL CHEMISTRY

286928 Fehling's solution 'A' is

1 aqueous copper sulphate

2 alkaline copper sulphate

3 alkaline solution of sodium potassium tartrate (Rochelle's salt)

4 aqueous sodium citrate

Explanation:

(a) Fehling solution ' A ' $=$ Aqueous ${CuSO}_{4}$ solution.
Fehling solution ' B ' = Alkaline sodium potassium Tartrate (Rochelle salt).

NCERT|Page-N-239|2024

PRACTICAL CHEMISTRY

286929 In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with ${Fe}^{3 +}$ due to the formation of

1

{Fe}_{4} {[Fe (CN)_{6}]}_{3} \cdot {xH}_{2} O

2 NaSCN

3

{[Fe (CN)_{5} NOS]}^{4 -}

4

[Fe (SCN)]^{2 +}

Explanation:

(d) In case, nitrogen and sulphur both are present in organic compound, sodium thiocyanate is formed. It gives blood red colour and no Prussian blue since there are no free cyanide ions.
$\begin{aligned} Na + C + N + S ⟶ & NaSCN \\ {Fe}^{3 +} + SCN ⟶⟶ & [Fe (SCN)]^{2 +} \\ Blood red \end{aligned}$
NOTES If sodium fusion is carried out with excess of sodium, the thiocyanate decomposes to yield cyanide and sulphide. These ions now give their usual tests.
$NaSCN + 2 Na ⟶ NaCH + {Na}_{2} S$

NCERT| Page-362 / N-284 | 2023

PRACTICAL CHEMISTRY

286930 Nitrogen detection in an organic compound is carried out by Lassaigne's test. The blue colour
formed corresponds to which of the following formulae?

1

{Fe}_{3} {[Fe (CN)_{6}]}_{3}

2

{Fe}_{3} {[Fe (CN)_{6}]}_{2}

3

{Fe}_{4} {[Fe (CN)_{6}]}_{3}

4

{Fe}_{4} {[Fe (CN)_{6}]}_{2}

Explanation:

(c) The prussian blue colour is of ${Fe}_{4} {[Fe (CN)_{6}]}_{3}$ ferric ferrocyanide.

Kar. 2013

PRACTICAL CHEMISTRY

286932 Lassaigne's test for the detection of nitrogen fails in

1

{NH}_{2} {CONHNH}_{2} \cdot HCl

2

{NH}_{2} {NH}_{2} \cdot HCl

3

{NH}_{2} {CONH}_{2}

4

C_{6} H_{5} {NHNH}_{2} \cdot HCl

Explanation:

(b) Hydrazine $({NH}_{2} {NH}_{2})$ does not contain carbon and hence on fusion with Na metal, it cannot form NaCN ; so it does not show Lassaigne's test for nitrogen.
NOTES This test fails in case of diazo compounds, dinitro compounds and compounds containing nitrogen in the ring.

NCERT| Page-354 / N-284 | 1994

PRACTICAL CHEMISTRY

286931 The Lassaigne's extract is boiled with conc. ${HNO}_{3}$ while testing for halogens. By doing so it

1 decomposes

{Na}_{2} S

and NaCN , if formed.

2 helps in the precipitation of AgCl .

3 increases the solubility product of AgCl .

4 increases the concentration of

{NO}_{3}^{-}

ions.

Explanation:

(a) Conc. ${HNO}_{3}$ decomposes NaCN and ${Na}_{2} S$ to avoid their interference.
$NaCN + {HNO}_{3} ⟶ {NaNO}_{3} + HCN ↑$
${Na}_{2} S + 2 {HNO}_{3} ⟶ 2 {NaNO}_{3} + H_{2} S ↑$

NCERT | Page-354 / N-284 | 2011

PRACTICAL CHEMISTRY

286928 Fehling's solution 'A' is

1 aqueous copper sulphate

2 alkaline copper sulphate

3 alkaline solution of sodium potassium tartrate (Rochelle's salt)

4 aqueous sodium citrate

Explanation:

(a) Fehling solution ' A ' $=$ Aqueous ${CuSO}_{4}$ solution.
Fehling solution ' B ' = Alkaline sodium potassium Tartrate (Rochelle salt).

NCERT|Page-N-239|2024

PRACTICAL CHEMISTRY

286929 In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with ${Fe}^{3 +}$ due to the formation of

1

{Fe}_{4} {[Fe (CN)_{6}]}_{3} \cdot {xH}_{2} O

2 NaSCN

3

{[Fe (CN)_{5} NOS]}^{4 -}

4

[Fe (SCN)]^{2 +}

Explanation:

(d) In case, nitrogen and sulphur both are present in organic compound, sodium thiocyanate is formed. It gives blood red colour and no Prussian blue since there are no free cyanide ions.
$\begin{aligned} Na + C + N + S ⟶ & NaSCN \\ {Fe}^{3 +} + SCN ⟶⟶ & [Fe (SCN)]^{2 +} \\ Blood red \end{aligned}$
NOTES If sodium fusion is carried out with excess of sodium, the thiocyanate decomposes to yield cyanide and sulphide. These ions now give their usual tests.
$NaSCN + 2 Na ⟶ NaCH + {Na}_{2} S$

NCERT| Page-362 / N-284 | 2023

PRACTICAL CHEMISTRY

286930 Nitrogen detection in an organic compound is carried out by Lassaigne's test. The blue colour
formed corresponds to which of the following formulae?

1

{Fe}_{3} {[Fe (CN)_{6}]}_{3}

2

{Fe}_{3} {[Fe (CN)_{6}]}_{2}

3

{Fe}_{4} {[Fe (CN)_{6}]}_{3}

4

{Fe}_{4} {[Fe (CN)_{6}]}_{2}

Explanation:

(c) The prussian blue colour is of ${Fe}_{4} {[Fe (CN)_{6}]}_{3}$ ferric ferrocyanide.

Kar. 2013

PRACTICAL CHEMISTRY

286932 Lassaigne's test for the detection of nitrogen fails in

1

{NH}_{2} {CONHNH}_{2} \cdot HCl

2

{NH}_{2} {NH}_{2} \cdot HCl

3

{NH}_{2} {CONH}_{2}

4

C_{6} H_{5} {NHNH}_{2} \cdot HCl

Explanation:

(b) Hydrazine $({NH}_{2} {NH}_{2})$ does not contain carbon and hence on fusion with Na metal, it cannot form NaCN ; so it does not show Lassaigne's test for nitrogen.
NOTES This test fails in case of diazo compounds, dinitro compounds and compounds containing nitrogen in the ring.

NCERT| Page-354 / N-284 | 1994

PRACTICAL CHEMISTRY

286931 The Lassaigne's extract is boiled with conc. ${HNO}_{3}$ while testing for halogens. By doing so it

1 decomposes

{Na}_{2} S

and NaCN , if formed.

2 helps in the precipitation of AgCl .

3 increases the solubility product of AgCl .

4 increases the concentration of

{NO}_{3}^{-}

ions.

Explanation:

(a) Conc. ${HNO}_{3}$ decomposes NaCN and ${Na}_{2} S$ to avoid their interference.
$NaCN + {HNO}_{3} ⟶ {NaNO}_{3} + HCN ↑$
${Na}_{2} S + 2 {HNO}_{3} ⟶ 2 {NaNO}_{3} + H_{2} S ↑$

NCERT | Page-354 / N-284 | 2011

PRACTICAL CHEMISTRY

286928 Fehling's solution 'A' is

1 aqueous copper sulphate

2 alkaline copper sulphate

3 alkaline solution of sodium potassium tartrate (Rochelle's salt)

4 aqueous sodium citrate

Explanation:

(a) Fehling solution ' A ' $=$ Aqueous ${CuSO}_{4}$ solution.
Fehling solution ' B ' = Alkaline sodium potassium Tartrate (Rochelle salt).

NCERT|Page-N-239|2024

PRACTICAL CHEMISTRY

286929 In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with ${Fe}^{3 +}$ due to the formation of

1

{Fe}_{4} {[Fe (CN)_{6}]}_{3} \cdot {xH}_{2} O

2 NaSCN

3

{[Fe (CN)_{5} NOS]}^{4 -}

4

[Fe (SCN)]^{2 +}

Explanation:

(d) In case, nitrogen and sulphur both are present in organic compound, sodium thiocyanate is formed. It gives blood red colour and no Prussian blue since there are no free cyanide ions.
$\begin{aligned} Na + C + N + S ⟶ & NaSCN \\ {Fe}^{3 +} + SCN ⟶⟶ & [Fe (SCN)]^{2 +} \\ Blood red \end{aligned}$
NOTES If sodium fusion is carried out with excess of sodium, the thiocyanate decomposes to yield cyanide and sulphide. These ions now give their usual tests.
$NaSCN + 2 Na ⟶ NaCH + {Na}_{2} S$

NCERT| Page-362 / N-284 | 2023

PRACTICAL CHEMISTRY

286930 Nitrogen detection in an organic compound is carried out by Lassaigne's test. The blue colour
formed corresponds to which of the following formulae?

1

{Fe}_{3} {[Fe (CN)_{6}]}_{3}

2

{Fe}_{3} {[Fe (CN)_{6}]}_{2}

3

{Fe}_{4} {[Fe (CN)_{6}]}_{3}

4

{Fe}_{4} {[Fe (CN)_{6}]}_{2}

Explanation:

(c) The prussian blue colour is of ${Fe}_{4} {[Fe (CN)_{6}]}_{3}$ ferric ferrocyanide.

Kar. 2013

PRACTICAL CHEMISTRY

286932 Lassaigne's test for the detection of nitrogen fails in

1

{NH}_{2} {CONHNH}_{2} \cdot HCl

2

{NH}_{2} {NH}_{2} \cdot HCl

3

{NH}_{2} {CONH}_{2}

4

C_{6} H_{5} {NHNH}_{2} \cdot HCl

Explanation:

(b) Hydrazine $({NH}_{2} {NH}_{2})$ does not contain carbon and hence on fusion with Na metal, it cannot form NaCN ; so it does not show Lassaigne's test for nitrogen.
NOTES This test fails in case of diazo compounds, dinitro compounds and compounds containing nitrogen in the ring.

NCERT| Page-354 / N-284 | 1994

PRACTICAL CHEMISTRY

286931 The Lassaigne's extract is boiled with conc. ${HNO}_{3}$ while testing for halogens. By doing so it

1 decomposes

{Na}_{2} S

and NaCN , if formed.

2 helps in the precipitation of AgCl .

3 increases the solubility product of AgCl .

4 increases the concentration of

{NO}_{3}^{-}

ions.

Explanation:

(a) Conc. ${HNO}_{3}$ decomposes NaCN and ${Na}_{2} S$ to avoid their interference.
$NaCN + {HNO}_{3} ⟶ {NaNO}_{3} + HCN ↑$
${Na}_{2} S + 2 {HNO}_{3} ⟶ 2 {NaNO}_{3} + H_{2} S ↑$

NCERT | Page-354 / N-284 | 2011

PRACTICAL CHEMISTRY

286928 Fehling's solution 'A' is

1 aqueous copper sulphate

2 alkaline copper sulphate

3 alkaline solution of sodium potassium tartrate (Rochelle's salt)

4 aqueous sodium citrate

Explanation:

(a) Fehling solution ' A ' $=$ Aqueous ${CuSO}_{4}$ solution.
Fehling solution ' B ' = Alkaline sodium potassium Tartrate (Rochelle salt).

NCERT|Page-N-239|2024

PRACTICAL CHEMISTRY

286929 In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with ${Fe}^{3 +}$ due to the formation of

1

{Fe}_{4} {[Fe (CN)_{6}]}_{3} \cdot {xH}_{2} O

2 NaSCN

3

{[Fe (CN)_{5} NOS]}^{4 -}

4

[Fe (SCN)]^{2 +}

Explanation:

(d) In case, nitrogen and sulphur both are present in organic compound, sodium thiocyanate is formed. It gives blood red colour and no Prussian blue since there are no free cyanide ions.
$\begin{aligned} Na + C + N + S ⟶ & NaSCN \\ {Fe}^{3 +} + SCN ⟶⟶ & [Fe (SCN)]^{2 +} \\ Blood red \end{aligned}$
NOTES If sodium fusion is carried out with excess of sodium, the thiocyanate decomposes to yield cyanide and sulphide. These ions now give their usual tests.
$NaSCN + 2 Na ⟶ NaCH + {Na}_{2} S$

NCERT| Page-362 / N-284 | 2023

PRACTICAL CHEMISTRY

286930 Nitrogen detection in an organic compound is carried out by Lassaigne's test. The blue colour
formed corresponds to which of the following formulae?

1

{Fe}_{3} {[Fe (CN)_{6}]}_{3}

2

{Fe}_{3} {[Fe (CN)_{6}]}_{2}

3

{Fe}_{4} {[Fe (CN)_{6}]}_{3}

4

{Fe}_{4} {[Fe (CN)_{6}]}_{2}

Explanation:

(c) The prussian blue colour is of ${Fe}_{4} {[Fe (CN)_{6}]}_{3}$ ferric ferrocyanide.

Kar. 2013

PRACTICAL CHEMISTRY

286932 Lassaigne's test for the detection of nitrogen fails in

1

{NH}_{2} {CONHNH}_{2} \cdot HCl

2

{NH}_{2} {NH}_{2} \cdot HCl

3

{NH}_{2} {CONH}_{2}

4

C_{6} H_{5} {NHNH}_{2} \cdot HCl

Explanation:

(b) Hydrazine $({NH}_{2} {NH}_{2})$ does not contain carbon and hence on fusion with Na metal, it cannot form NaCN ; so it does not show Lassaigne's test for nitrogen.
NOTES This test fails in case of diazo compounds, dinitro compounds and compounds containing nitrogen in the ring.

NCERT| Page-354 / N-284 | 1994

PRACTICAL CHEMISTRY

286931 The Lassaigne's extract is boiled with conc. ${HNO}_{3}$ while testing for halogens. By doing so it

1 decomposes

{Na}_{2} S

and NaCN , if formed.

2 helps in the precipitation of AgCl .

3 increases the solubility product of AgCl .

4 increases the concentration of

{NO}_{3}^{-}

ions.

Explanation:

(a) Conc. ${HNO}_{3}$ decomposes NaCN and ${Na}_{2} S$ to avoid their interference.
$NaCN + {HNO}_{3} ⟶ {NaNO}_{3} + HCN ↑$
${Na}_{2} S + 2 {HNO}_{3} ⟶ 2 {NaNO}_{3} + H_{2} S ↑$

NCERT | Page-354 / N-284 | 2011

PRACTICAL CHEMISTRY

286928 Fehling's solution 'A' is

1 aqueous copper sulphate

2 alkaline copper sulphate

3 alkaline solution of sodium potassium tartrate (Rochelle's salt)

4 aqueous sodium citrate

Explanation:

(a) Fehling solution ' A ' $=$ Aqueous ${CuSO}_{4}$ solution.
Fehling solution ' B ' = Alkaline sodium potassium Tartrate (Rochelle salt).

NCERT|Page-N-239|2024

PRACTICAL CHEMISTRY

286929 In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with ${Fe}^{3 +}$ due to the formation of

1

{Fe}_{4} {[Fe (CN)_{6}]}_{3} \cdot {xH}_{2} O

2 NaSCN

3

{[Fe (CN)_{5} NOS]}^{4 -}

4

[Fe (SCN)]^{2 +}

Explanation:

(d) In case, nitrogen and sulphur both are present in organic compound, sodium thiocyanate is formed. It gives blood red colour and no Prussian blue since there are no free cyanide ions.
$\begin{aligned} Na + C + N + S ⟶ & NaSCN \\ {Fe}^{3 +} + SCN ⟶⟶ & [Fe (SCN)]^{2 +} \\ Blood red \end{aligned}$
NOTES If sodium fusion is carried out with excess of sodium, the thiocyanate decomposes to yield cyanide and sulphide. These ions now give their usual tests.
$NaSCN + 2 Na ⟶ NaCH + {Na}_{2} S$

NCERT| Page-362 / N-284 | 2023

PRACTICAL CHEMISTRY

286930 Nitrogen detection in an organic compound is carried out by Lassaigne's test. The blue colour
formed corresponds to which of the following formulae?

1

{Fe}_{3} {[Fe (CN)_{6}]}_{3}

2

{Fe}_{3} {[Fe (CN)_{6}]}_{2}

3

{Fe}_{4} {[Fe (CN)_{6}]}_{3}

4

{Fe}_{4} {[Fe (CN)_{6}]}_{2}

Explanation:

(c) The prussian blue colour is of ${Fe}_{4} {[Fe (CN)_{6}]}_{3}$ ferric ferrocyanide.

Kar. 2013

PRACTICAL CHEMISTRY

286932 Lassaigne's test for the detection of nitrogen fails in

1

{NH}_{2} {CONHNH}_{2} \cdot HCl

2

{NH}_{2} {NH}_{2} \cdot HCl

3

{NH}_{2} {CONH}_{2}

4

C_{6} H_{5} {NHNH}_{2} \cdot HCl

Explanation:

(b) Hydrazine $({NH}_{2} {NH}_{2})$ does not contain carbon and hence on fusion with Na metal, it cannot form NaCN ; so it does not show Lassaigne's test for nitrogen.
NOTES This test fails in case of diazo compounds, dinitro compounds and compounds containing nitrogen in the ring.

NCERT| Page-354 / N-284 | 1994