Acetic acid: pKa = 4.76 Sulfuric acid: pKa2 = 1.99 Citric acid: pKa1 = 3.10, pKa2 = 4.35, pKa3 = 6.3 — Analytical Chemistry Chemistry Question
Acid-Base Equilibria and pH Calculations
Acetic acid: pKa = 4.76
Sulfuric acid: pKa2 = 1.99
Citric acid: pKa1 = 3.10, pKa2 = 4.35, pKa3 = 6.39
Calculate the analytical concentration for each of the following solutions:
HCl solution, pH = 4.00 (solution A),
Model Answer
[H3O+] = 1×10−4
c(HCl)total = 1×10−4 mol dm–3
Calculate the analytical concentration for each of the following solutions:
acetic acid solution, pH = 4.00 (solution B),
Model Answer
[H3O+] = 1×10−4
Mass balance: [HAc]total = [Ac−] + [HAc]
Charge balance: [H3O+] = [Ac−]
Ka = [H3O+][Ac−] / [HAc]
[HAc]total = [H3O+] + [H3O+]2 / Ka
[HAc]total = 6.75×10−4
Calculate the analytical concentration for each of the following solutions:
sulfuric acid solution, pH = 4.00 (solution C),
Model Answer
[H3O+] = 1×10−4
Mass balance: [H2SO4]total = [HSO4−] + [SO42−]
Charge balance: [H3O+] = [HSO4−] + 2[SO42−]
Ka2 = [H3O+][SO42−] / [HSO4−]
The solution of the equations gives:
[H2SO4]total = 5.024×10−5
Calculate the analytical concentration for each of the following solutions:
citric acid solution, pH = 4.00 (solution D).
Model Answer
[H3O+] = 1×10−4
Mass balance: [H3A]total = [H3A] + [H2A−] + [HA2−] + [A3−]
Charge balance: [H3O+] = [H2A−] + 2 [HA2−] + 3 [A3−]
Ka1 = [H3O+][H2A−] / [H3A]
Ka2 = [H3O+][HA2−] / [H2A−]
Ka3 = [H3O+][A3−] / [HA2−]
[H3A]total = 8.29×10−5
Calculate the pH for each of the following mixtures:
equal volumes of solution A and NaOH solution (pOH = 4),
Model Answer
In the mixture of equal volumes of HCl and NaOH solutions [HCl]total = 5.00×10−5 and [NaOH]total = 5.00×10−5 ) the resulting solution is neutral and pH = 7.00.
Calculate the pH for each of the following mixtures:
equal volumes of solution B and NaOH solution (pOH = 4),
Model Answer
In the mixture [HAc]total = 3.375×10−4 and [NaOH]total = 5.00×10−5
Material balance: [HAc]total = [Ac−] + [HAc]
Charge balance: [H3O+] + [Na+] = [Ac−]
Ka = [H3O+][Ac−] / [HAc]
[H3O+] = 4.46×10−5 and [NaOH]total = [Na+]
pH = 4.35
Calculate the pH for each of the following mixtures:
equal volumes of solution C and NaOH solution (pOH = 4),
Model Answer
In the mixture [H2SO4]total = 2.512×10−5 and [NaOH]total = 5.00×10−5 , and thus, this solution is nearly neutral.
Material balance: [H2SO4]total = [HSO4−] + [SO42−], and [NaOH]total = [Na+]
Charge balance: [H3O+] + [Na+] = [HSO4−] + 2[SO42−] + [OH−]
Kw = [H3O+]·[OH−] = 1.00×10−14
Ka2 = [H3O+][SO42−] / [HSO4−]
[H3O+] = 2.76×10−7 pH = 6.56
Calculate the pH for each of the following mixtures:
equal volumes of solution D and NaOH solution (pOH = 4).
Model Answer
In the mixture [H3A]total = 4.145×10−5 and [NaOH]total = 5.00×10−5, the resulting solution contains: [NaH2A]total = 3.29×10−5 and [Na2HA]total = 8.55×10−6
Ka2 = [H3O+][HA2−] / [H2A−] = [H3O+]([Na2HA]total + [H3O+]) / ([NaH2A]total − [H3O+])
[H3O+] = 2.00×10−5 pH = 4.70
Calculate the pH for each of the following mixtures:
equal volumes of solution A and B,
Model Answer
In the mixture [HAc]total = 3.375×10−4 and [HCl]total = 5.00×10−5,
Material balance: [HAc]total = [Ac−] + [HAc] and [HCl]total = [Cl−]
Charge balance: [H3O+] = [Ac−] + [Cl−]
Ka = [H3O+][Ac−] / [HAc]
[H3O+] = 9.99×10−5 pH = 4.00
Calculate the pH for each of the following mixtures:
equal volumes of solution A and C.
Model Answer
In mixture [H2SO4]total = 2.512×10−5 and [HCl]total = 5.00×10−5
Material balance: [H2SO4]total = [HSO4−] + [SO42−] and [HCl]total = [Cl−]
Charge balance: [H3O+] = [HSO4−] + 2[SO42−] + [Cl−]
Ka2 = [H3O+][SO42−] / [HSO4−]
[H3O+] = 1.00×10−4 pH = 4.00