Question

Calculate Ka for 1 M NaCH3COO

pH = 9.37

H+ = 4.203 X 10^-10

OH- = 2.402 X 10^-5

CH3COO- = 1.00 X 10^0

CH3COOH = 2.402 X 10^-5

________________

Calculate Ka using the formula

Kw = Ka X Kb and the appropriate equilibrium constant for 1 M NaCH3COO.

NaCH3COO ---> Na+ (neutral) + CH3COO-.

Is the conjugate base for CH3COOH.

CH3COOH Ka1 = 1.8 X 10^-5

______________________

Calculate Ka for 1 M NH4Cl

pH = 4.26

H+ = 2.336 X 10^-5

OH- = 4.267 X 10^-10

NH4+ = 1.00 X 10^0

NH3 = 2.366 X 10^-5

_____________________

Calculate Ka using the formula

Kw = Ka X Kb and the appropriate equilibrium constant for NH4Cl

NH4Cl = conjugate acid NH3..

NH3 Kb1 = 1.76 X 10^-5

Please show me how you got these ... Thank you

Answer 1

Ka, _CH3COOH = [H+][ CH3COO- ]/[ CH3COOH ] = 1.75x 10^-5

………………….

You have to calculate Kb of CH3COO-, not a Ka.

K_b = 10^-14 / K_a,CH3COOH = 10^-14 / 1.8 X 10^-5 = 5.5x10^-10

……………………..

K_a,NH4+ = [NH3][ H+]/[ NH4+ ] =

            = 2.366 X 10^-5 x 2.366 X 10^-5 / 1.00 X 10^0 =

             = 5.60 x 10^-10

………………………….

You have to calculate K_a,NH4+ using the value of K_b,NH3

K_a,NH4+ = 1x10^-14 / K_b,NH3 = 1x10^-14 / 1.76 X 10^-5 = 5.68 x10^-10

Note: Kw = 1x10^-14