Chemistry

CBSE Class 12

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11.

Copper crystallises with face centred cubic unit cell. If the radius of a copper atom is 127.8 pm, calculate the density of the copper metal.

(Atomic mass of Cu = 63.55 u and Avogadro’s number N_{A} = 6.02 x 10^{23} mol^{-1})

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12.

Iron has a body centred cubic unit cell with the cell dimension of 286.65 pm. The density of iron is 7.87 g cm^{-3}. Use this information to calculate Avogadro’s number. (Atomic mass of Fe = 56.0 u)

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The reaction N_{2}(g) + O_{2}(g) * * 2NO(g), contributes to air pollution whenever a fuel is burnt in air at a high temperature. At 1500 K, equilibrium constant K for it is 1.0 x 10^{-5}. Suppose in a case [N_{2}] = 0.80 mol L^{-1}and [O_{2}] = 0.20 mol L^{-1} before any reaction occurs. Calculate the equilibrium concentrations of the reactants and the product after the mixture has been heated to 1500 K.

N_{2}(g) + O_{2}(g) 2NO(g)

T=0 0.8 0.20

T=t 0.8-x 0.2-x 2x

K_{c} = 1.0 x 10^{-5}

K_{c} =

Or, 1.0 x 10^{-5} = (2x)^{2}/ [(0.8 – x)(0.2 – x )]

If *x* is very small, then

0.8 – x 0.8

0.2 – x 0.2

1.0 x 10^{-5} = (2x)^{2} / [(0.80) (0.2)]

16 x (10-6) = 4 x2

X^{2} = 2 x 10^{-3}

Therefore, the amount of reactant and product at equilibrium is as follows:

N^{2} = 0.8 - 0.002 = 0.798

O^{2} = 0.2 - 0.002 = 0.198

NO = 2*x* = 2 x 2 x 10^{-3} = 4 x 10^{-3}

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14.

The electrical resistance of a column of 0.05 M NaOH solution of diameter 1cm and length 50

cm is 5.55 x 10^{3} ohm. Calculate its resistivity, conductivity and molar conductivity.

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15.

Write three distinct features of chemisorptions which are not found in physisorptions.

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16.

Explain each of the following observations:

(i) With the same d-orbital configuration (*d*^{4}), Cr^{2+} is a reducing agent while Mn^{3+} is an oxidising agent.

(ii) Actinoids exhibit a much larger number of oxidation states than the lanthanoids.

(iii) There is hardly any increase in atomic size with increasing atomic number in a series of transition metals.

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17.

Name of the following coordination entities and describe their structure:

(i) [Fe (CN)_{6}]^{4-}

(ii) [Cr (NH_{3})_{4}Cl_{2}]^{+}

(iii) [Ni (CN)_{ 4}]^{2-}

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20.

Write a reaction which shows that all the carbon atoms in glucose are linked in a straight chain.

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