With respect to the Hall Heroult process related to the extraction of aluminium, justify the following:

(a) Powdered Coke is sprinkled over the electrolytic mixture undergoing electrolytic reduction.

(b) Graphite anodes are continuously replaced during the electrolysis.

(c) Cryolite and fluorspar must be added to the electrolytic mixture.

Write complete and balanced equations for the reactions occurring in the following cases:

(a) Passing dry ammonia gas over heated lead oxide placed in a combustion tube to produce a silvery grey metal.

(b) When concentrated nitric acid is reacted with zinc to produce a reddish-brown gas.

(c) When concentrated sulphuric acid oxidises sulphur to produce a gas which turns acidified potassium dichromate paper green.

Rohan wants to electroplate a spoon with nickel.

(a) To which electrode should he connect the article to be electroplated?

(b) Write the equation for the reaction that will occur at the cathode.

(c) What should the anode be made up of?

Amit found that 30g of a gas occupied 1000 c.c at STP.

(a) What will the gram molecular weight and the vapour density of this gas be?

(b) How many molecules of this gas will be present in 44.8 l of it?