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Standard XII
Chemistry
Nucleophilic Substitution Reaction
When a white ...
Question

When a white crystalline compound X is heated with K2Cr2O7 and concentrated H2SO4, a reddish brown gas A is evolved. On passing A into caustic soda solution, a yellow-colored solution B is obtained. Neutralizing the solution of B with acetic acid and on subsequent addition of lead acetate, a yellow precipitate C is obtained. When X is heated with NaOH solution, a colorless gas is evolved and on passing this gas into K2HgI4 solution, a reddish-brown precipitate D is formed.

Identify D.

A
Hg2I2
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B
H2N−Hg−O−Hg−I
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C
HgI2
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D
Hg(NH2)2
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Solution

The correct option is B H2N−Hg−O−Hg−I
When a white crystalline compound X is heated with K2Cr2O7 and concentrated H2SO4, a reddish-brown gas A is evolved. This must be chromyl chloride coming from a chloride salt. On passing A into caustic soda solution, a yellow-colored solution B is obtained. This is sodium chromate. Neutralizing the solution of B with acetic acid and on subsequent addition of lead acetate, a yellow precipitate C is obtained. This is lead chromate. When X is heated with NaOH solution, a colorless gas is evolved and on passing this gas into K2HgI4 solution, a reddish-brown precipitate D is formed. The gas is ammonia, so A is ammonium chioride. D is iodide of Millon's base.
K2Cr2O7+2H2SO4⟶2KHSO4+2CrO3+H2O
NH4Cl+H2SO4⟶NH4HSO4+HCl
CrO3+2HCl⟶CrO2Cl2+H2OOrangeredvapors
NaOH+CrO2Cl2⟶Na2CrO4+NaCl+H2OYellowsolution
Pb(CH3COO)2+Na2CrO4⟶PbCrO4↓+CH3COONaYellowppt.
NH4Cl+NaOH⟶NaCl+H2O+NH3
2K2HgI4+NH3+3KOH⟶NH2−Hg−O−Hg−I+7KI+2H2O
H2N−Hg−O−Hg−I is brown colored iodide of Millon's base

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Q. A imparts green color to the flame. Its solution does not give a precipitate on passing H2S. When it is heated with solid K2Cr2O7 and conc. H2SO4, reddish brown gas is evolved. The gas when passed in an aqueous solution of NaOH turns it yellow. Find out A.
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An aqueous solution of salt (A), gives white crystalline precipitate (B) with NaCl solution. The filtrate gives a black precipitate (C) when H2S is passed through it. Compound (B) is dissolves in hot water and the solution gives a yellow precipitate (D) on treating with NaI and cooling. The compound (A) does not give any gas with dilute HCl but liberates reddish brown gas on heating.

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A black colored compound (A) on reaction with dil.H2SO4 gives a gas (B) which on passing in a solution of acid (C) gives white turbidity (D). Gas (B) when passed in an acidified solution of a compound (E) gives a black precipitate (F) which is soluble in hot concentrated (C). After boiling this solution when an excess of ammonia solution is added, a blue-colored compound (G) is formed. To the solution of (E), on the addition of acetic acid and aqueous potassium ferrocyanide, a chocolate brown precipitate (H) is formed. On the addition of an aqueous solution of BaCl2 to an aqueous solution of (E), white precipitate insoluble in HNO3 is obtained.

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Q. Solid KCl, when heated with solid K2Cr2O7 and concentrated H2SO4, gives red vapours (a) that turn NaOH solution yellow (b). The yellow solution, when acidified with acetic acid and treated with lead acetate, gives a yellow precipitate (c). Which of the following is true with respect to a, b and c?
Q. An aqueous solution of salt (A) gives a white crystalline precipitate (B) with NaCl solution. The filtrate gives a black precipitate (C) when H2S is passed through it. Compound (B) dissolves in hot water and the solution gives yellow precipitate (D) on treatment with potassium iodine and on cooling. The compound (A) does not give any gas with dilute HCl but liberates a reddish brown gas on heating. Compounds (A) to (D) are identified as:
(A) : Pb(NO3)3 , (B) : PbCl2 (C) : PbS, (D) : PbI2
If true enter 1, else enter 0.
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