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Of physisorption or chemisorption, which has a higher enthalpy of adsorption?
Chemisorption has a higher enthalpy of adsorption as compared to physisorption.
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Name the method used for refining of copper metal.
The electrolytic method is used for refining copper metal.
(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.
How are interhalogen compounds formed? What general compositions can be assigned to them?
An interhalogen compound is a molecule which contains two or more different halogen atoms. A most interhalogen compound known are binary. Their formula is generally XYn Where n=1, 3, 5, or 7 and X is the less electronegative of two halogens. On hydrolysis, they ionise to give rise to poly -halogen ion. For example
Br2 (l) + F2 (g) --> 2BrF (g)
Draw the structures of the following molecules:
(i) XeF6
(ii) H2S2O7
(i) Structure of XeF6 :
(ii) H2S2O7
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