(a) Why does the presence of an excess of lithium make LiCl crys

Subject

Chemistry

Class

CBSE Class 12

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 Multiple Choice QuestionsShort Answer Type

1.

Of physisorption or chemisorption, which has a higher enthalpy of adsorption? 

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2.

Name the method used for refining of copper metal.

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3.

(a) Why does the presence of an excess of lithium make LiCl crystals pink?

(b) A solid with cubic crystal is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body-center. What is the formula of the compound? 


(a) When crystals of LiCl is heated in presence of excess of lithium, Cl- ions from crystal diffuse on the surface and combine with ionized Li to form LiCl. The released unpaired electrons occupy the anionic sites known as F-centers. The pink colour results by excitation of these electrons when they absorb energy from visible light falling on them.

(b) It is given that the atoms of Q are present at the corners of the cube. Therefore, number of atoms of Q in one unit cell =

Also, it is also given that the atoms of P are present at the body-center.

Therefore, number of atoms of P in one unit cell = 1

This means that the ratio of the number of P atoms to the number of Q atoms, P: Q = 1:1

Hence, the formula of the compound is PQ.

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4.

How are interhalogen compounds formed? What general compositions can be assigned to them?

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5.

Draw the structures of the following molecules:

(i) XeF6

(ii) H2S2O7

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6.

Aluminum crystallizes in an fcc structure. Atomic radius of the metal is 125 pm. What is the length of the side of the unit cell of the metal? 

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7.

The standard electrode potential (E°) for Daniell cell is +1·1 V. Calculate the   G° for the reaction

Zn(s) + Cu2+ (aq)  ----> Zn+ (aq) + Cu (s)

(1 F = 96500 C mol-1).

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8.

(a) For a reaction A + B -->  P, the rate law is given by,

r = k [A]1/2 [B]2.

What is the order of this reaction?

(b) A first order reaction is found to have a rate constant k = 5·5 x 10-14 s-1. Find the half-life of the reaction. 

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9.

Outline the principles of refining of metals by the following methods: 

(i) Zone refining

(ii) Vapour phase refining

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10.

Define the following terms giving an example of each:

(i) Associated colloids

(ii) Lyophilic sol

(iii) Adsorption

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