Final answer:
The pH at the equivalence point when 50 ml of 0.10M formic acid is treated with 0.10M sodium hydroxide can be calculated by considering the hydrolysis of the formed sodium formate in water.
Step-by-step explanation:
Calculating pH at the Equivalence Point for a Weak Acid-Strong Base Titration
To calculate the pH at the equivalence point when 50 ml of 0.10M formic acid, HCHO₂, is treated with 0.10M sodium hydroxide, we need to understand that at the equivalence point of a titration of a weak acid with a strong base, the solution contains the conjugate base of the weak acid in water. In this case, when HCHO₂ is titrated with NaOH, we'll form sodium formate (HCOONa) and water. Since sodium formate is a salt originating from a weak acid and a strong base, it will hydrolyze in solution.
The reaction can be written as:
HCOO⁻(aq) + H₂O(l) → HCOOH(aq) + OH⁻(aq).
The concentration of the sodium formate in the solution at the equivalence point will be equal to the initial concentration of formic acid because the number of moles of NaOH added will equal the number of moles of HCHO₂ originally present. This is because NaOH and HCHO₂ react in a 1:1 mole ratio.
In this scenario, the concentration of sodium formate in the solution at the equivalence point will be 0.050 M.
To find the pH, we need to calculate the pOH of the solution using the hydrolysis of the formate ion (HCOO⁻) and then use the relationship that pH + pOH = 14 to find the pH. The pH at the equivalence point for a weak acid-strong base titration is typically greater than 7, because the hydrolysis of the formed salt produces hydroxide ions, making the solution basic.
By using an appropriate equilibrium expression for the hydrolysis reaction and the ionization constant (Kb) of the formate ion, which is derived from the Ka of formic acid, we can calculate the concentration of hydroxide ions and thus the pOH. Unfortunately, without the specific value of Ka or Kb, we cannot perform these calculations exactly, but this is the general process to follow to determine the pH at the equivalence point.