Question

30. Using the data in the table, which of the conjugate bases below is the strongest base?

Acid	Ka
HOAc	1.8 x 10-5
HC7H5O2	6.3 x 10-5
HNO2	4.5 x 10-4
HF	6.8 x 10-4

[A] F⁻ [B] C₇H₅O₂⁻ [C] OAc⁻ [D] NO₂⁻ [E] OAc^- and C₇H₅ O₂⁻

Answer 1

Ans :- Option (c) is the correct answer i.e.  OAc^- is the strongest base.

Explanation :-

Larger is the value of K_b (i.e. dissociation constant for base) , stronger will be the conjugate base.

We know,

K_b = 1.0 x 10^-14/K_a

(a). For OAc^- i.e. conjugate base of HOAc acid.

K_b = 1.0 x 10^-14/1.8 x 10^-5  

K_b = 5.55 x 10^-10 (Larger)

(b). For C₇H₅O₂^- i.e. conjugate base of HC₇H₅O₂ acid.

K_b = 1.0 x 10^-14/6.3 x 10^-5

K_b = 1.59 x 10^-10  

(c). For NO₂^- i.e. conjugate base of HNO₂ acid.

K_b = 1.0 x 10^-14/4.5 x 10^-4

K_b = 2.22 x 10^-11  

(d). For F^- i.e. conjugate base of HF acid.

K_b = 1.0 x 10^-14/6.8 x 10^-4

K_b = 1.47 x 10^-11  

Hence, Option (c) is the correct answer i.e.  OAc^-