25 mL of standardized 0.45 mol/L NaOH is titrated with 21 mL of 0.35 mol/L acetic acid. Calculate the pH of the solution

To calculate the pH of the solution, we first need to determine the concentration of the acetic acid and the concentration of the acetate ion formed when it reacts with NaOH.

1. Write the balanced chemical equation for the reaction between acetic acid (CH3COOH) and sodium hydroxide (NaOH):
CH3COOH + NaOH → CH3COONa + H2O

2. Calculate the number of moles of acetic acid used:
moles of acetic acid = volume × concentration
moles of acetic acid = 21 mL × 0.35 mol/L = 7.35 mmol

3. Since acetic acid and sodium hydroxide react in a 1:1 ratio, the number of moles of sodium hydroxide used is also 7.35 mmol.

4. Now we can calculate the concentration of sodium hydroxide remaining after the reaction:
moles of sodium hydroxide remaining = moles of sodium hydroxide initially - moles of sodium hydroxide used
moles of sodium hydroxide remaining = moles of sodium hydroxide initially - moles of acetic acid used

Since initially we had 25 mL of 0.45 mol/L NaOH:
moles of sodium hydroxide initially = volume × concentration
moles of sodium hydroxide initially = 25 mL × 0.45 mol/L = 11.25 mmol

moles of sodium hydroxide remaining = 11.25 mmol - 7.35 mmol
moles of sodium hydroxide remaining = 3.9 mmol

5. Now we need to calculate the concentration of the acetate ion (CH3COO-) formed from the reaction. Since the solution after the reaction is a solution of sodium acetate (CH3COONa), the concentration of the acetate ion will be the same as the remaining concentration of sodium hydroxide.

Concentration of acetate ion = moles of the acetate ion / volume of the solution
Concentration of acetate ion = 3.9 mmol / (21 mL + 25 mL) = 3.9 mmol / 46 mL

6. Since acetic acid is a weak acid, its dissociation into hydrogen ions (H+) and acetate ions (CH3COO-) is described by the following equilibrium reaction:

CH3COOH ↔ H+ + CH3COO-

We can assume that the reaction has reached equilibrium because the volumes involved are relatively small. At equilibrium, the concentration of hydrogen ions (H+) will be equal to the concentration of the acetate ion (CH3COO-).

Concentration of hydrogen ions (H+) = concentration of acetate ion (CH3COO-)

7. Now we can calculate the pH of the solution by taking the negative logarithm (base 10) of the concentration of hydrogen ions:
pH = -log [H+]

pH = -log [CH3COO-]

pH = -log (3.9 mmol / 46 mL)

Calculating the final pH requires the use of a logarithm function.

I think you posted this yesterday. And I think I remembers suggesting that you had the numbers reversed. Anyway, tell me what you know and show the work you've done and I can help you through it. Start by writing the equation and calculating the mols of each reactant present before reaction begins.