8/8/2019 Computations - Exp7

1/1

Computations:

Part A.

CaCl2 + H2O 2Cl- + Ca(OH)2

Ca(OH)2 Ca2+ + 2OH-

M1V1 = M2V2(0.1M CaCl2)(0.25ml) = M2(1.25ml)M2 = 0.02 M CaCl2[Ca2+] = 0.02 M

Test tube A:

NH4OH NH4+ + OH- NH3 + H2O

M1V1 = M2V2(1 M NH4OH)(0.25ml) = M2(1.25ml)M2 = 0.2 M NH4OH = [NH3]

Kb, NH3 = 1.76 x 10-5

1.76 x 10-5 = [NH4+][OH-]/[NH3]

1.76 x 10-5 = x2/0.2X = 1.88 x 10-3

[OH-] = 2 x 10-3 M[Ca2+] = 0.02 M

Ion Product = [Ca2+][OH-]2 = (0.02)(2 x 10-3)2 = 8 x 10-8

Test tube B:NaOH Na+ + OH-

M1V1 = M2V2(1 M NaOH)(0.25ml) = M2(1.25ml)M2 = 0.2 M NaOH = [OH

-]

Ion Product = (0.02 M)(0.2 M)2 = 8 x 10-4

Test tube C:

NaOAc Na+ + OAc-

OAc- + H2O HOAc + OH-

M1V1 = M2V2(3 M NaOAc)(0.25ml) = M2(1.25ml)M2 = 0.6 M NaOAc = [OAc

-]

Kb = Kw / 1.8 x 10-5 = x2 / 0.6

x = 1.8 x 10-5 M = [OH-]

Ion Product = (0.02 M)(1.8 x 10-5)2 = 6 x10-12

Test tube D:

NH4OH NH4+ + OH- NH3 + H2O

NH4Cl NH4+ + Cl-

NH4+ + OH- NH3 + H2O

M1V1 = M2V2

(3 M NH4OH)(0.25 ml) = M2(1.25 ml)M2 = 0.6 M NH4OH

(4 M NH4Cl)(0.75ml) = M2(1.25ml)M2 = 2.4 M NH4Cl

Kb, NH3 = x (2.4 + x) / 0.6 = 1.8 x 10-5

2.4x + x2 = 1.08 x 10-5

X = 4.5 x 10-6 = 5 x 10-6 = [OH-]

Ion Product = (0.02 M)(5 x 10-6)2 = 5 x 10-13