1
Question
(i) An inorganic compound (A) is formed on passing a gas (B) through a concentrated liquor containing sodium sulphide and sodium sulphite.
(ii) On adding (A) into a dilute solution of silver nitrate, a white precipitate appears which quickly changes into a black compound (C).
(iii) On adding two or three drops of ferric chloride into the excess of solution of (A), a violet coloured compound (D) is formed. This colour disappears quickly.
(iv) On adding a solution (A) into the solution of cupric chloride, a white precipitate is first formed which dissolves on adding an excess of (A) forming a compound (E).
(A) to (E) are (A) : Na2S2O3
(B) : SO2
(C) : Ag2S
(D) : [Fe(S2O3)2]− (violet, immediately changes to colourless)
(E) : Na4[Cu6I(S2O3)5]
If the given statement is true enter 1, else enter 0.
(ii) On adding (A) into a dilute solution of silver nitrate, a white precipitate appears which quickly changes into a black compound (C).
(iii) On adding two or three drops of ferric chloride into the excess of solution of (A), a violet coloured compound (D) is formed. This colour disappears quickly.
(iv) On adding a solution (A) into the solution of cupric chloride, a white precipitate is first formed which dissolves on adding an excess of (A) forming a compound (E).
(A) to (E) are (A) : Na2S2O3
(B) : SO2
(C) : Ag2S
(D) : [Fe(S2O3)2]− (violet, immediately changes to colourless)
(E) : Na4[Cu6I(S2O3)5]
If the given statement is true enter 1, else enter 0.
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Solution
(i) Na2S2O3 is formed on passing SO2 gas through a concentrated liquor containing sodium sulphide and sodium sulphite.
Na2SO3+2Na2S+3SO2⟶3Na2S2O3(A)
(ii) On adding Na2S2O3 into a dilute solution of silver nitrate, a white precipitete of Ag2S2O3 appears which quickly changes into a black Ag2S.
: 2AgNO3+Na2S2O3⟶Ag2S2O3↓white+2NaNO3
Ag2S2O3+H2O⟶Ag2Sblack↓+H2SO4
(iii) On adding two or three drops of ferric chloride into the excess of solution of Na2S2O3, a violet coloured compound
[Fe(S2O3)2]− is formed.
This colour disappears quickly.
A dark violet coloration is due to formation of dithiosulphato iron (III) complex (D)
2S2O32−+Fe3+⟶[Fe(S2O3)2]−
This colour disappears rapidly due to formation of S4O2−6 and Fe2+
[Fe(S2O3)2]−+Fe3+⟶2Fe2++S4O2−6
(iv) On adding a solution Na2S2O3 into the solution of cupric chloride, a white precipitate is first formed which dissolves on adding
excess of Na2S2O3 forming a compound
Na4[Cu6I(S2O3)5] sodium cupro (I) thiosulphate complex.
2CuCl2+3Na2S2O3⟶Cu2S2O3white↓+Na2S4O6+4NaCl
3Cu2S2O3+2Na2S2O3⟶Na4[Cu6(S2O3soluble)5]
Na2SO3+2Na2S+3SO2⟶3Na2S2O3(A)
(ii) On adding Na2S2O3 into a dilute solution of silver nitrate, a white precipitete of Ag2S2O3 appears which quickly changes into a black Ag2S.
: 2AgNO3+Na2S2O3⟶Ag2S2O3↓white+2NaNO3
Ag2S2O3+H2O⟶Ag2Sblack↓+H2SO4
(iii) On adding two or three drops of ferric chloride into the excess of solution of Na2S2O3, a violet coloured compound
[Fe(S2O3)2]− is formed.
This colour disappears quickly.
A dark violet coloration is due to formation of dithiosulphato iron (III) complex (D)
2S2O32−+Fe3+⟶[Fe(S2O3)2]−
This colour disappears rapidly due to formation of S4O2−6 and Fe2+
[Fe(S2O3)2]−+Fe3+⟶2Fe2++S4O2−6
(iv) On adding a solution Na2S2O3 into the solution of cupric chloride, a white precipitate is first formed which dissolves on adding
excess of Na2S2O3 forming a compound
Na4[Cu6I(S2O3)5] sodium cupro (I) thiosulphate complex.
2CuCl2+3Na2S2O3⟶Cu2S2O3white↓+Na2S4O6+4NaCl
3Cu2S2O3+2Na2S2O3⟶Na4[Cu6(S2O3soluble)5]
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