[5 Mark Question Answer]

Question 15 Marks

State your observations when ammonium hydroxide solution is added drop by drop and then in excess to each of the following solutions :
1) Copper sulphate solution
2) Zinc sulfate solution.

Answer

When $NH _4 OH$ is added to copper sulphate solution drop-wise, a pale blue ppt. is obtained.
$CuSO_4+2 NH_4 OH \longrightarrow Cu(OH)_2+\left(NH_4\right)_2 SO_4+4 H_2 O$
With the excess of $NH _4 OH$, the ppt. dissolves to give a deep blue solution of tetraamine copper(II)sulphate
$Cu(OH)_2+\left(NH_4\right)_2 SO_4+2 NH_4 OH \longrightarrow\left[Cu\left(NH_3\right)_4\right]_{SO_4}+4 H_2 O$
2) When $NH _4 OH$ is added to zinc sulphate solution drop-wise, a white, gelatinous ppt. is obtained.
$ZnSO_4+2 NH_4 OH \longrightarrow Zn(OH)_2+\left(NH_4\right)_2 SO_4$
With the excess of NH 4 OH , the ppt. dissolves to give a colorless solution of tetraamine zinc(II)sulphate.$Zn(OH)_2+\left(NH_4\right)_2 SO_4+2 NH_4 OH \longrightarrow\left[Zn\left(NH_3\right)_4\right] SO_4+4 H_2 O$

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Question 25 Marks

From the list given below, select the word (s) required complete the blanks (i) to (v) in the following passage :
Note : words chosen from the list are to be used only once. Write only the answers. Do not copy the passage
[reddish brown, ammonium, nitrogen dioxide, hydroxyl, dirty green, ammonia, acidic, alkaline]
Nitrogen and hydrogen combine in the presence of a catalyst to give (i) ________ gas. When the above mentioned gas is passed through water it forms a solution which will be (ii) ______ in nature and the solution contains (iii) ______ ions and (iv) _______ions. The above solution when added to iron (II) sulphate solution gives a (v) _________coloured precipitate of iron (II) hydroxide.

Answer

(i) Ammonia
(ii) Alkaline
(iii) Ammonium
(iv) Hydroxyl
(v) Dirty green

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Question 35 Marks

The questions (i) to (v) refer to the following salt solutions listed A to F :
A. Copper nitrate
B. Iron (II) sulphate
C. Iron (III) chloride
D. Lead nitrate
E. Magnesium sulphate
F. Zinc chloride
(i) Which two solutions will give a white precipitate when treated with dilute hydrochloric acid followed by barium chloride solution/
(ii) Which two solutions will give a white precipitate when treated with dilute nitric acid followed by silver nitrate solution?
(iii) Which solution will give a white precipitate when either dilute hydrochloric acid or dilute sulphuric acid is added to it?
(iv) Which solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it?
(v) Which solution gives a white precipitate with excess ammonium hydroxide?

Answer

(i) B and E (Iron (II) sulphate and Magnesium sulphate)
(ii) C and F (Iron (III) chloride and Zinc chloride)
(iii) D (Lead nitrate)
(iv) A (Copper nitrate)
(v) F (Zinc chloride)

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Question 45 Marks

Sodium hydroxide solution is added first in a small quantity, then in excess to the aqueous salt solutions of copper (II) sulphate, zinc nitrate, lead nitrate, calcium chloride and iron (III) sulphate. Copy the following table and write the colour of the precipitate in (i) to (v) and the nature of the precipiatate (soluble or insoluble) in (vi) to (x)

Aqueous salt Solution	Colour of Participitate when NaOH is added in a samll quantity	Nature of precipitate(soluble or insoluble) when NaOH added in excess
Copper (II) Solution
Zinc nitrate
Lead nitrate
Calcium chloride
Iron(III) sulphate

Answer

Aqueous salt Solution	Colour of Participitate when NaOH is added in a samll quantity	Nature of precipitate(soluble or insoluble) when NaOH added in excess
Copper (II) Solution	Blue	Insoluble
Zinc nitrate	White	Soluble
Lead nitrate	White	Soluble
Calcium chloride	White	Sparingly soluble
Iron(III) sulphate	Reddish Brown	Insoluble

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Question 55 Marks

You are given three white powders-calcium carbonate, lead carbonate and zinc carbonate. Describe the tests you would carry out in solution, to identify the metal ion in each of the above compounds. Indicate clearly how you would prepare the solutions for the tests.

Answer

The solutions for the tests will be prepared by dissolving the given powders separately in water.
(i) Solution of Calcium carbonate:
Calcium carbonate is $CaCO _3$ and contains $Ca ^{2+}$ ions. Sodium hydroxide solution NaOH can be used to identify $Ca ^{2+}$ since its addition to calcium carbonate solution will give white precipitates of $Ca ( OH )_2$ which are sparingly soluble in excess of NaOH .
(ii) Solution of Lead carbonate:
Lead carbonate is $PbCO _3$ and contains $Pb ^{2+}$ ions. Ammonium hydroxide solution $NH _4 OH$ can be used to identify $Pb ^{2+}$ since its addition to lead carbonate solution will give white precipitates of $Pb ( OH )_2$ which are insoluble in excess of $NH _4 OH$.
(iii) Solution of Zinc carbonate:
Zinc carbonate is $ZnCO _3$ and contains $Zn ^{2+}$ ions. Sodium hydroxide solution NaOH can be used to identify $Zn ^{2+}$ since its addition to zinc carbonate solution will give white gelatinous precipitates of $Zn ( OH )_2$ which are soluble in excess of NaOH .

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Question 65 Marks

You are provided with $PbCO_3, ZnCO_3$ and $CaCO_3$. How will you identify these cations?

Answer

By use of Ammonium hydroxide we can identify the ions $PbCO _3, ZnCO _3$ and $CaCO _3$ as:
(i)
$
PbCO _3+2 NH _4 OH \longrightarrow Pb ( OH )_2 \downarrow+2 NH _4 NO _3
$
$Ob ( OH )_2$ forms white precipitate which are insoluble in excess ammonium hydroxide.
ii)
$
ZnCO _3+ NH _4 OH \longrightarrow Zn ( OH )_2 \downarrow+2 Na _2 CO _3
$
$Zn ( OH )_2$ forms white gelatinous precipitate which are soluble in excess ammonium hydroxide. iii)
$
CaCO _3+ NH _4 OH \longrightarrow Ca ( OH )_2+2 Na _2 CO _3
$
No precipitation of $Ca ( OH )_2$ occurs even with addition of excess of $NH _4 OH$. Because the concentration of hydroxide ion from ammonium hydroxide is so low that it cannot precipitate the hydroxide of calcium.
Concept Insight : Some precipitated metallic hydroxides by ammonium hydroxide become soluble aydroxides when treated with excess of ammonium hydroxide due to the formation of a soluble complex salt in the presence of excess of ammonium hydroxide.

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