Question

Please show answer and work!

0.15 M KCHO2 Express your answer to two decimal places.

pH =

Part B 0.15 M CH3NH3I Express your answer to two decimal places.

pH =

Part C 0.16 M KI, two decimal places and also find pH=

Answer 1

KCHO2 --> K+ + CHO2-

NOTE... asume this is formate ion

so

pKa = 3.75

Ka = 1.8*10^-4

Kb = (10^-14)/( 1.8*10^-4) = 5.55*10^-11

so..

CHOO- + H2O <--> CHOOH + OH-

Kb = [CHOOH][OH-]/[CHOO-]

5.55*10^-11 = x*x/(0.15-x)

x = 2.885*10^-6

[OH-] = x = 2.885*10^-6

pOH= -log(2.885*10^-6) = 5.53

ph = 14-5.53 = 8.47

b)

CH3NH3I --> CH3NH3+ + I-

CH3NH3+ <--> CH3NH2 + H+

Ka = [CH3NH2 ][H+]/[CH3NH3+]

Kb = 4.4*10^-4

then

Ka = (10^-14)/(4.4*10^-4) = 2.27*10^-11

Ka = [CH3NH2 ][H+]/[CH3NH3+]

2.27*10^-11 = x*x/(0.15-x)

x = H+ = 1.85*10^-6

pH = -log(1.85*10^-6) = 5.7328

c)

KI --> K+ +I-

this will not form any equilibria

so

pH = 7