1.) If a buffer solution is 0.110 M in a weak base (Kb = 5.7 × 10-5) and 0.590 M
ID: 944897 • Letter: 1
Question
1.) If a buffer solution is 0.110 M in a weak base (Kb = 5.7 × 10-5) and 0.590 M in its conjugate acid, what is the pH?
2.) You need to prepare 100.0 mL of a pH=4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.240 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
3.) Calculate the change in pH when 6.00 mL of 0.100 M HCl(aq) is added to 100.0 mL of a buffer solution that is 0.100 M in NH3(aq) and 0.100 M in NH4Cl(aq). A list of ionization constants can be found here. Calculate the change in pH when 6.00 mL of 0.100 M NaOH(aq) is added to the original buffer solution.
Explanation / Answer
The list is not present, please proivde the list for the 3 problem, remaining two answers are posted
Using the hessley henderbach equation
pOH = pKb + log[Conjugatea acid/Weak Base]
pOH = 5 - log(5.7) + log(5.3636)
pOH = 5 - log(1.0627) = 4.973
pH = 14 - 4.973 = 9.026
2)
pH = pKa + log(sodium benzoate/acid)
4 = 4.20 + log(sodium benzoate/acid)
sodium benzoate = 10^(-0.20) * [acid] = 0.6309 [acid]
V/1000 * 0.240 = 0.6309 * (100-V)/1000 * 0.100
4.804V = 100
V = 20.81 mL
Volume of base = 20.81 (sodium benzoate)
Volume of acid = 100 - 20.81 = 79.19 mL
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