Question

6. NHI can react with BFs, forming NHMBFs. In this reaction, A the NHI acts as a Bronsted base, accepting a proton from the BF molecule. B. the NHI acts as a Lewis base, donating a proton to the BF, molecule. C. the NHacts as a Brunsted acid, donating a proton to the BF, molecule. D. the BF, molecule acts as a Lewis acid, accepting an electron pair from the NH3 molecule to form a coordinate covalent bond. E the BFs molecule acts as a Lewis base, donating an electron pair to the NHs molecule to form a coordinate covalent bond. 7. Which of the following ions is the strongest Lewis acid? A Na B. Clo c . CHCOO D. Mg . All 8. The pH of a 0.50 M solution of the weak acid HA is 4.76. The value of K. is A. 6.0 x 10-10 B. 1.7 x 109 at C. 3.5 x 10% D. 7.6 x 10+ E. 9.24

Answer 1

6. Ans :- Option (D) i.e. " the BF₃ molecule act as a lewis acid , accepting a electron pair from the NH₃ molecule to form a coordinate covalent bond "is the correct answer.

Explanation :-

Lewis acids :- Are electron deficient species.

Lewis Base :- Are electron rich species.

Because, in BF₃ octet of B is incomplete i.e. have 6 electrons only, therefore it is Lewis acid and NH₃ has a lone pair on N atom which donate its electron pair to electron deficient BF₃ molecule and form a coordinate covalent bond.

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7. Ans :- Option (E) i.e. " Al³⁺" is the correct answer.

Explanation :-

Because, Al³⁺ has more tendency to accept a pair of electrons due to its smaller size and hence it is stronger Lewis acid.

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8. Ans :- Option (A) i.e. " 6.0 x 10^-10  " is the correct answer.

Explanation :-

For weak acid

[H⁺] = Cα

Here,

C = Concentration of weak acid = 0.50 M (given)

α = Degree of dissociation = ? and

[H⁺] = 10^-pH = 10^-4.76 = 1.74 x 10^-5 M

Now,

α = [H⁺]/C = 1.74 x 10^-5 M / 0.50 M = 3.48 x 10^-5

Also,

Acid dissociation constant (K_a) = Cα² = (0.50).(3.48 x 10^-5 )² = 6.0 x 10^-10