Question

(8 pts) Comparing dissociation constants, circle the strongest base in the following pairs. You must justify your reasoning and show any calculations to receive credit. 5. Circle the strongest base in the pair: A. CsHsN and NHs and (pyridine and ammonia bases) Justification: B. PO. and AsO. and (phosphate and arsenate) Justification:

Answer 1

5)

A)

K_b of C5H5N = 1.5 x 10^-9

K_b of NH₃ = 1.8 x 10^-5

If K_b values is large then that is strong base. So, Kb of NH3 is large . So it is strongest base

NH3 has strongest base

B)

HAsO₄^2- is weak acid than HPO₄^2- .The conjugate base of weak acid is strong base.

Here HAsO₄^2- is weak.So the base of AsO₄^3- is strongest base.

6)

Given data,

pH = 1.55

Concentration = 2.3 M

We know pH = -log(H+)

H+ = 10^-1.55

H+ = x = 0.0281 M

We know , K_a = x² / C - x

= ( 0.0281 )² / 2.3 - 0.0281

= 0.0007896 / 2.271

Ka = 3.47 x 10^-4