Q1 of 55 Page 1

On what principle is the method of zone refining of metals based?

The method of zone refining of metals is based on the principle that the impurities are more soluble in molten(hot) metal then in solid(cooled) metal. In this method, a bar of impure metal is passed through a heating element in the form of a ring. As the metal gets heated the impurities dissolve in the hot molten metal, as the heating element moves the heated metal gets cooled and solidified, while the impurities move with the molten metal leaving behind a metal of very high purity. This method is used to purify metals like germanium, indium gallium etc.


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29

A) Account for the following:

1) Bi is a strong oxidising agent in the +5 state.


2) is known but is not known.


3) dissolves in HCl to form and not


B) Draw the structures of the following:


1)


2)


OR


A) Draw the structures of the following:


i)


ii) Red


B) Account for the following:


i) Sulphur is vapour state exhibits paramagnetism


ii) Unlike, Xenon, no distinct chemical compound of Helium is known.


iii) is a stronger reducing agent than .


30

A) i) Write the products formed when ethanal reacts with the following reagents:

a) and then


b)


c) in the presence of dil NaOH


B) Give simple chemical tests to distinguish between the following pairs of compounds:


i) Benzoic acid and Ethyl benzoate


ii) Propanal and Butan-2-one


OR


I) Account for the following:


i) is more reactive than towards the reaction with HCN.


ii) groups in semicarbazide (). However, only one is involved in the formation of semicarbazone.


II) Write the chemical equation to illustrate each of the following name reactions.


i) Rosenmund reduction


ii) Hell-Vohlard-Zelinsky reaction


iii) Cannizzaroreaction


 2

Name the temperature above which the formation of micelles takes place.

 3

Arrange the following in the increasing order of their basicity: