Calculate the theoretical pH at the starting point and at each equivalence point for phosphoric acid, acetic acid, and sulfuric acid. Please show the equilibrium equation, the Ka, and the pH calculation.
I could write a book on this but I don't have the time. Here is how you do acetic acid. The others are done the same way.
CH3COOH + NaOH(for example) ==> CH3COONa + H2O
So the pH at the equivalence point is determined by the hydrolysis of the salt.
CH3COO^- + HOH ==> CH3COOH + OH^-
Kb = (Kw/Ka) = (CH3COOH)(OH^-)/(CH3COO^-)
This is as far as you can go on ANY of the above until you have a concentration of each acid.
After you have that, Kw = 1E-14
Ka = Ka for CH3COOH from your text or notes.
(CH3COOH) = x
(OH^-) = x
(CH3COO^-) = Molarity -x
Solve for x (which is OH^-), then convert to pOH using pOH = -log(OH^-) and use
pH + pOH = pKw = 14 and solve for pH.
Post your work if you get stuck.
To calculate the theoretical pH at the starting point and each equivalence point for phosphoric acid, acetic acid, and sulfuric acid, we need to analyze their dissociation in water and consider the equilibrium equations and equilibrium constants (Ka).
1. Phosphoric acid (H₃PO₄):
Starting point:
H₃PO₄ ↔ H⁺ + H₂PO₄⁻
Equilibrium equation: [H₃PO₄] = [H⁺] + [H₂PO₄⁻]
Ka₁ = ([H⁺] [H₂PO₄⁻]) / [H₃PO₄]
First equivalence point:
H₂PO₄⁻ ↔ H⁺ + HPO₄²⁻
Equilibrium equation: [H₂PO₄⁻] = [H⁺] + [HPO₄²⁻]
Ka₂ = ([H⁺] [HPO₄²⁻]) / [H₂PO₄⁻]
Second equivalence point:
HPO₄²⁻ ↔ H⁺ + PO₄³⁻
Equilibrium equation: [HPO₄²⁻] = [H⁺] + [PO₄³⁻]
Ka₃ = ([H⁺] [PO₄³⁻]) / [HPO₄²⁻]
To calculate the theoretical pH, we use the equation:
pH = -log[H⁺] = -log(Ka) + log([H₃PO₄] - [H⁺] eqm)
2. Acetic acid (CH₃COOH):
Starting point:
CH₃COOH ↔ H⁺ + CH₃COO⁻
Equilibrium equation: [CH₃COOH] = [H⁺] + [CH₃COO⁻]
Ka = ([H⁺] [CH₃COO⁻]) / [CH₃COOH]
To calculate the theoretical pH, we use the equation:
pH = -log[H⁺] = -log(Ka) + log([CH₃COOH] - [H⁺] eqm)
3. Sulfuric acid (H₂SO₄):
Starting point:
H₂SO₄ ↔ 2H⁺ + SO₄²⁻
Equilibrium equation: [H₂SO₄] = 2[H⁺] + [SO₄²⁻]
Ka = ([H⁺]² [SO₄²⁻]) / [H₂SO₄]
To calculate the theoretical pH, we use the equation:
pH = -log[H⁺] = -log(Ka) + log([H₂SO₄] - 2[H⁺] eqm)
It's important to note that these calculations assume that the acids are monoprotic (phosphoric acid), weak acids (acetic acid), and fully dissociate (sulfuric acid) in water. It's also important to consider the initial concentrations of the acid and the added base during the titration.