Question

1. What quantity (moles) of NaOH must be added to 1.0 L of 2.1 M HC2H3O2 to produce a solution buffered at pH = 4.00? Ka = 1.8×10-5 mol

2. What quantity (moles) of NaOH must be added to 1.0 L of 2.1 M HC2H3O2 to produce a solution buffered at pH = 5.00? Ka = 1.8×10-5 mol

I really need help! Please show every step of the math no matter how small! Thank you

Answer 1

1)

moles of acetic acid = 1 x 2.1 = 2.1

pH = 4.00

pKa = 4.74

CH3COOH + NaOH --------------> CH3COO- + H2O

    2.1                x                                 0                   0

2.1 - x              0                                 x                    x

pH = pKa + log [salt / acid]

4.00 = 4.74 + log [x / 2.1 - x]

[x / 2.1 - x] = 0.182

x = 0.3233

moles of NaOH = 0.32 moles