I need help starting this question:
A buffer solution is prepared by adding 30.0g of pure acetic acid to 41.0g of sodium acetate in water, and then diluting the solution to 1.00L. What is the pH of the buffer solution?
To determine the pH of the buffer solution, we need to understand the nature of the acetic acid and sodium acetate reaction in water.
Acetic acid (CH3COOH) is a weak acid, which means it does not completely dissociate in water. It partially ionizes, releasing hydrogen ions (H+) into the solution:
CH3COOH ⇌ CH3COO- + H+
The sodium acetate (CH3COONa), on the other hand, is a salt made up of a weak acid and its conjugate base. It completely dissociates in water, providing acetate ions (CH3COO-) and sodium ions (Na+):
CH3COONa → CH3COO- + Na+
The buffer solution is created by combining these components. The acetic acid supplies the weak acid, and the sodium acetate supplies the conjugate base.
To calculate the pH of the buffer solution, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA]),
where pH is the desired pH of the buffer solution, pKa is the negative logarithm of the acid dissociation constant (Ka) of the weak acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.
To proceed with the calculation, we need to determine the concentration of acetate ions ([A-]) and the concentration of acetic acid ([HA]) in the solution.
To find the concentration of acetate ions, we need to convert the mass of sodium acetate (41.0g) to moles. Sodium acetate has a molar mass of 82.0 g/mol.
41.0g / 82.0 g/mol = 0.500 mol
Since we diluted the solution to 1.00L, the concentration of acetate ions becomes:
0.500 mol / 1.00 L = 0.500 M
Next, we need to find the concentration of acetic acid. We convert the mass of acetic acid (30.0g) to moles. Acetic acid has a molar mass of 60.0 g/mol.
30.0g / 60.0 g/mol = 0.500 mol
Again, since we diluted the solution to 1.00L, the concentration of acetic acid becomes:
0.500 mol / 1.00 L = 0.500 M
Now that we have the concentrations of acetate ions ([A-]) and acetic acid ([HA]), we can calculate the pH using the Henderson-Hasselbalch equation. However, we need one more piece of information: the pKa of acetic acid. The pKa for acetic acid is 4.76.
Substituting the values into the equation:
pH = 4.76 + log (0.500 M/0.500 M)
pH = 4.76 + log (1)
pH = 4.76 + 0
pH = 4.76
Therefore, the pH of the buffer solution is 4.76.