Question

A buffer is prepared by adding 20.0 g of acetic acid (HC2H3O2) and 20.0 g of sodium acetate (NaC₂H₃O₂) to enough water to form 2.00 L of solution. (Ka = 1.8 x 10⁻⁵)

determine the pH of the buffer

Answer 1

To calculate the pH of the buffer, the molarity of acetic acid and sodium acetate in the solution is determined, and then the Henderson-Hasselbalch equation is applied using these molarities and the pKa value of acetic acid.

Step-by-step explanation:

Calculating the pH of a Buffer Solution

To determine the pH of the buffer solution composed of acetic acid and sodium acetate, we employ the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

Firstly, calculate the molar masses of acetic acid (HC₂H₃O₂, 60.05 g/mol) and sodium acetate (NaC₂H₃O₂, 82.03 g/mol) to find their respective moles:

• 
  
• Moles of acetic acid = 20.0 g / 60.05 g/mol ≈ 0.333 mol
• 
  
• Moles of sodium acetate = 20.0 g / 82.03 g/mol ≈ 0.244 mol

Next, calculate the molarity of each component in the 2.00 L solution:

• 
  
• Molarity of acetic acid = 0.333 mol / 2.00 L = 0.167 M
• 
  
• Molarity of sodium acetate = 0.244 mol / 2.00 L = 0.122 M

Applying these values to the Henderson-Hasselbalch equation with pKa = -log(1.8 x 10⁻⁵) ≈ 4.74:

pH = 4.74 + log(0.122 / 0.167)

This equation will yield the final pH value of the buffer solution.