Question

For the following questions refer to the table below.

Acids	Ka
HNO2	4.0 x 10-4
HCl	3.1 x 106
HCN	6.2 x 10-10
HClO4	> 1.0 x 1010
H2SO4	1.0 x 103
HBrO	2.0 x 10-9
HIO3	1.6 x 10-1

Rank the following bases from strongest to weakest base.

NO₂^-, Cl^-, CN^-, ClO₄^-, BrO^-

What are the following Kb values at 25 ᵒC?

CN^-

BrO^-

NO₂^-

HSO₄-

Which acid from the table would be the weakest acid?

Answer 1

strongest base --> will acept H+ readily

weakest base --> is a very strong acid

for:

NO2-, Cl-, CN-, ClO4-, BrO-

weak acids = HNO2, HCN, HBrO, HCl, HClO4

Ka order --> HCN < HBrO < HNO2 < HCl < HClO4

strongest base, CN-> BrO- > NO2- > Cl- > ClO4-

What are the following Kb values at 25 ᵒC?

Kw = Ka*Kb always valid, at 25°C = Kw = 10^14

Kb = Kw/Ka = (10^-14)/(Ka)

CN- --> kb = (10^-14)/(Ka) = (10^-14)/(6.2*10^-10) = 1.61*10^-5

BrO---> kb = (10^-14)/(Ka) = (10^-14)/(2*10^-9) = 5*10^-6

NO2----> kb = (10^-14)/(Ka) = (10^-14)/(4*10^-4) = 2.5*10^-11

HSO4-----> kb = (10^-14)/(Ka) = (10^-14)/(10^3) = 2*10^-17

Which acid from the table would be the weakest acid?

Must be HCN, since has the lowest Ka

HCN 6.2 x 10-10