For a first order reaction, show that time required for 99% completion is double of the time required for the completion of 90% of reaction.

OR

The rate constant of a first order reaction increases from 4 x 10^-2 to 24 x 10^-2 , when the temperature changes from 300 K to 350 K. Calculate the energy of activation (E_a). [ Given: log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021, log 6 = 0.7782; R = 8.314 J/K/mol]

Determine the type of cubic lattice to which ion crystal belongs if its unit cell has an edge length of 300pm and density of iron is 7.2g cm^-1. [Atomic mass of Fe = 56 g mol^-1; N_A = 6.02 x 10²³ mol^-1]

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of1.62K. calculate the van’t Hoff factor and predict the nature of solute (associated/ dissociated). [ Given: molar mass of benzoic acid = 122 g mol^-1 , K_f(H₂O) = 1.86 K Kg mol^-1]

(a) Indicate the principle behind the method for the refining of zinc.

(b) Account for the following:

(i) It is advantageous to roast sulphide ore to oxide before reduction.

(ii) Zinc oxide can be reduced to metal by heating with carbon but not Cr₂O₃.

Account for the following:

(a) Inter-halogen compounds are more reactive than pure halogens.

(b) Nitrogen is less reactive at room temperature.

(c) Reducing character increases from NH₃ to BiH₃.