Q24 of 26 Page 1

Calculate the emf and for the following cell at 298K:


OR


(a) Give reasons for the following:


(i) Iron does not rust even if zinc coating is broken in galvanized pipe.


(ii) Copper sulphate solution cannot be stored in zinc container.


(b) The molar conductivity of 0.025 mol L-1 methanoic acid is 46.1S cm2mol-1. Calculate its degree of dissociation and dissociation constant.


[Given: λoH+ = 349.6 S cm2 mol-1 ; λoHCOO- = 54.6 S cm2 mol-1]


cell reaction:

Magnesium acts as anode while silver acts as cathode in this cell.





OR


(a) (i) Zinc has a higher reduction potential than iron. Zinc comes higher up in the galvanic series. When zinc coating is broken in galvanized pipe a cell is formed such that zinc acts as anode (undergoes oxidation) while iron will be cathode, so iron does not undergo oxidation hence no rusting.


(ii) Zinc is more reactive than copper, so when copper sulphate solution is stored in zinc container zinc displaces copper to form zinc sulphate and precipitates copper. Hence copper sulphate solution cannot be stored in zinc containers.


(b) Concentration = C = 0.025 mol L-1


λHCOOH = 46.1 S cm2mol-1


λoHCOOH = λoHCOO- + λoH+ = 54.6 + 349.6 = 404.2 S cm2 mol-1


Degree of dissociation = α = λHCOOH / λoHCOOH = 46.1/404.2 = 0.114


Dissociation constant =



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22

Give one example for each of the following:

(a) An artificial sweetener whose use is limited to cold drinks.


(b) A non-ionic detergent.


(c) A pain reliever used for relief from severe pain like post-operative pain.


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Aadik Behl was playing in the park with his friends. While running to catch a ball, one of his friends, Saurish fell down and he had a cut on his hand due to which lot of blood was coming out. Aadik took him to his house and applied alum on the cut due to which the blood stopped.

Answer the following questions:


(a) Why did the blood stop after applying alum on the cut?


(b) Alum is used for purification of water. Why?


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(d) What are the values (any two) displayed by Aadik?


 25

(a) Why do actinoids show a wide range of oxidation states? Write one similarity between the chemistry of lanthanoids and actinoids.

(b) Second I.E. of chromium and copper are exceptionally higher than that of their neighbouring elements. Explain.


(c) Zinc has lowest energy of atomization in 3d-series. Why?


OR


(a) Give reasons for the following:


(i) Transition metals are paramagnetic.


(ii) Transition metals show variable oxidation states.


(iii) Zr and Hf have nearly similar atomic radii.


(b) Write the preparation of KMnO4 from pyrolusite ore(MnO2).


 26

(a) How do you convert the following?

(i) Phenol to benzene


(ii) Ethanol to ethane


(b) Give the chemical tests to distinguish between the following pairs of compounds:


(i) Ethanol and phenol


(ii) Butan-2-ol and 2-methylpropan-2-ol


(c) Write the IUPAC name of



OR


(a) Write the mechanism for the preparation of alcohols from alkenes (acid catalysed hydration).


(b) Give reasons for the following:


(i) Phenols do not undergo substitution of the –OH group, like alcohols.


(ii) p-nitrophenol is more acidic than p-methylphenol.