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CBSE Class 12 Chemistry Solved Question Paper 2018

Short Answer Type

11.

Give reasons for the following:

Aquatic animals are more comfortable in the cold water than in warm water.

12.

Give reasons for the following:

Elevation of the boiling point of 1 M KCl solution is nearly double than that of 1 M sugar solution.

13.

Write the formula of the following coordination compound :
Iron(III) hexacyanoferrate (II)

14.

What type of isomerism is exhibited by the complex [Co(NH₃)₅ Cl]SO₄?

15.

Write the hybridisation and number of unpaired electrons in the complex [CoF₆]^3-.

Atomic No. of Co = 27

16.

Identify the chiral molecule in the following pair :

17.

Give reason:

E° value for a Mn³⁺/Mn²⁺ couple is much more positive than that for Fe3⁺/Fe²⁺.

18.

Give reason:

Iron has a higher enthalpy of atomization than that of copper.

19.

Sc³⁺ is colourless in aqueous solution whereas Ti³⁺ is coloured.

20.
Write the chemical reactions involved in the process of extraction of Gold. Explain the role of dilute NaCN and Zn in this process

The roasted ore of gold is leached with a solution of sodium cyanide in the presence of oxygen for many days. The role of NaCN in this process is to dissolve the gold to form an aurocyanide complex, from which the metal is obtained by displacement.

$4 A u + 8 N a C N + 2 H_{2} O + O_{2} \overset{}{\to} 4 N a [A u (C N)_{2}] + 4 K O H 2 N a [A u (C N)_{2}] + Z n \overset{}{\to} N a_{2} [Z n (C N)_{4}] + 2 A u$