Question 1

First and second ionization enthalpies of lithium are 520 kJ mol^ -1 and 7297 kJ mol^ -1 respectively. Energy required to convert 3.5 mg lithium (g) into Li ^ 2+ (g) [ Li(g) Li ^ 2+ (g) ] is _______ k

Accepted Answer

The total energy required to convert 1 mole of Li(g) to Li ^ 2+ (g) is the sum of the first and second ionization enthalpies: E = IE_1 + IE_2 = 520 + 7297 = 7817 kJ mol ^ -1 Given mass of lithium = 3.5 mg = 3.5 10^ -3 g Number of moles of lithium = 3.5 10^ -3 g 7 g mol ^ -1 = 5 10^ -4 mol Energy required for 5 10^ -4 mol of Li is: Energy = 5 10^ -4 mol 7817 kJ mol ^ -1 = 3.9085 kJ Rounding to the nearest integer, we get 4 KJ. Answer: 4

Question 2

The correct set that contains all kinds (basic, acidic, amphoteric and neutral) of oxides is:

Accepted Answer

K_2O is a metallic oxide and is basic in nature. Cl_2O_7 is a non-metallic oxide with a high oxidation state and is acidic in nature. As_2O_3 is a metalloid oxide and is amphoteric in nature. NO is a neutral oxide. Thus, the set K_2O, Cl_2O_7, As_2O_3 and NO contains all kinds of oxides. Answer: K_2 O, Cl_2 O_7, As_2 O_3 and NO

s Block Elements — Previous Year Questions & Solutions