Long Answer Type(i) Write the equation which relates the number of phases, components and degree of freedom of a system in equilibrium.
(ii) How many phases and components are there in a system consisting of:
(1) a mixture of O2 and N2 gases
(2) N2 gas containing H2O vapour
(3) a mixture of ice and water
(4) a mixture of powdered iron and sulphur
(5) a lump of solid iron (II) sulphide
Give a suitable explanation, in brief, for your answer.
Consider the reaction,
A + B → C + D
The initial rates for different initial concentrations of the reactants are given below :
Initial concentration (mol 1– 1Initial rate (mol 1 –1 s– 1)
|
A |
B |
||
|
(i) |
1.0 |
1.0 |
2.0 x 10 – 3 |
|
(ii) |
2.0 |
1.0 |
4.0 x 10– 3 |
|
(iii) |
4.0 |
1.0 |
8.0 x 10– 3 |
|
(iv) |
1.0 |
2.0 |
2.0 x 10– 3 |
|
(v) |
1.0 |
4.0 |
2.0 x 10’3 |
(a) What are the orders with respect to A and B ?
(b) What is the overall order ?
(c) Write the rate law equation.
(d) Calculate the rate constant.
(e) Suggest a possible mechanism.
Explain the principle involved in the following observations :
(i) Cu2+ is precipitated as CuS in the acidic medium while Ni2+ is precipitated as NiS in a basic medium with H2S.
(ii) A solution of a weak acid and its salt with strong base has a definite pH value which does not change appreciably on dilution.
(iii) A solution of sodium chloride is neutral while that of ferric chloride is acidic in nature.
(i) Why could fluorine not be prepared for a long time from HF and metal fluorides either by electrolysis or by any chemical reaction ?
(ii) Describe the modern method for the preparation of fluorine by giving :
(a) Materials used in the construction of the cell.
(b) Electrolyte used.
(c) Electrode reactions.
(i) Fluorine could not be prepared for a long time because it is very reactive in nature and reacted with the material of the vessels. Also the aqueous solution of H2F2 produced H2.,S and O3 mixed with O2 and not the fluorine. On the other hand anhydrous H2F2 was found to be non-conductor of electricity.
(ii) Moissan’s method : This method was used for the first time by Moissan to isolate the fluorine.
(a) Electrolytic cell : The electrolytic cell was made of Pt-Ir alloys cooled at -23°C by placing it in a bath of CH3Cl which was renewed constantly.
(b) Electrolyte : A solution of potassium hydrogen fluoride (KHF2) and anhydrous hydrofluoric acid (H2F2) in the ratio of 1 : 5 was used as the electrolyte.
(c) Electrode reactions : Both the electrodes were made of Pt-Ir alloy and the reactions that took place were as follows :
At anode:
F- -e- --> F
F+F ----> F2
At cathode:
H+ +e- ---> H
H+H --> H2
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