Question

For each of the following solutions, calculate the initial pH and the final pH after adding...

For each of the following solutions, calculate the initial pH and the final pH after adding 0.0200 mol of NaOH.

Part A

For 290.0 mL of pure water, calculate the initial pH and the final pH after adding 0.0200 mol of NaOH.

Part B

For 290.0 mL of a buffer solution that is 0.200 M in HCHO2 and 0.310 M in KCHO2, calculate the initial pH and the final pH after adding 0.0200 mol of NaOH(Ka=1.8⋅10−4).

Part C

For 290.0 mL of a buffer solution that is 0.2975 M in CH3CH2NH2 and 0.2675 M in CH3CH2NH3Cl, calculate the initial pH and the final pH after adding 0.0200 mol of NaOH(Kb=5.6⋅10−4).

I CAN'T FIGURE THIS ONE OUT!

part A

for pure water pH = 7

concentration of solution = 0.02/0.29 = 0.07 M

pOH = -log(OH-)

= -LOG0.07 = 1.155

pH = 14-1.155 = 12.845

part B

No of mol of HCHO2 = 0.2*0.29 = 0.058 mol

No of mol of KCHO2 = 0.31*0.29 = 0.09 mol

pH = pka + log(salt/acid)

pka = -logKa = -log(1.8*10^-4) = 3.74

= 3.74+log(0.09/0.058)

= 3.93

= 3.74+log((0.09+0.02)/(0.058-0.02))

= 4.21

part C

No of mol of CH3CH2NH2 = 0.2975*0.29 = 0.0863 mol

No of mol of KCHO2 = 0.2675*0.29 = 0.078 mol

pOH = pkb + log(salt/base)

pkb = -logKa = -log(5.6*10^-4) = 3.252

= 3.252+log(0.078/0.0863)

= 3.21

pH = 14-3.21 = 10.79

= 3.252+log((0.078-0.02)/(0.0863+0.02))

= 2.99

pH = 14-2.99 = 11.01