Calculate the pH during the titration of 10.00 mL of 0.400 M hypochlorous acid with 0.500 M NaOH.
The Ka for HOCl is 3.0 x 10-8 M.
What is the pH at the equivalence point?
I used the HH formula and got pH=7.52+log(.222)=6.87, but its not right.
To calculate the pH at the equivalence point during the titration of hypochlorous acid (HOCl) with sodium hydroxide (NaOH), we need to consider the reaction that occurs between these two compounds.
Hypochlorous acid (HOCl) is a weak acid, while sodium hydroxide (NaOH) is a strong base. During the titration, the weak acid (HOCl) will react with the strong base (NaOH) to form the salt sodium hypochlorite (NaOCl) and water (H2O).
The balanced chemical equation for the reaction is:
HOCl + NaOH → NaOCl + H2O
We can assume that the reaction goes to completion because NaOH is a strong base.
Since HOCl is a weak acid, it undergoes partial ionization in water according to the equilibrium:
HOCl(aq) ⇌ H+(aq) + OCl-(aq)
The Ka value provided (3.0 x 10^-8 M) represents the acid dissociation constant for HOCl.
To determine the pH at the equivalence point, we need to find the volume of NaOH required to completely react with the 10.00 mL of 0.400 M HOCl.
First, calculate the number of moles of HOCl:
moles of HOCl = volume of HOCl (L) × concentration of HOCl (M)
moles of HOCl = 0.01000 L × 0.400 M = 0.00400 moles
Since the reaction between HOCl and NaOH is a 1:1 ratio, the same number of moles of NaOH will react with HOCl.
Next, calculate the volume of NaOH required to react with 0.00400 moles using its concentration:
volume of NaOH (L) = moles of NaOH / concentration of NaOH (M)
volume of NaOH = 0.00400 moles / 0.500 M = 0.00800 L = 8.00 mL
Therefore, 8.00 mL of 0.500 M NaOH is required to reach the equivalence point in the titration.
At the equivalence point, the moles of NaOH will completely react with the moles of HOCl, resulting in a solution that contains only the salt NaOCl and water. The pH of the solution will depend on the hydrolysis of the salt.
In this case, NaOCl will hydrolyze to form the hypochlorite ion (OCl-) and hydroxide ion (OH-):
NaOCl(aq) + H2O(l) ⇌ Na+(aq) + OCl-(aq) + OH-(aq)
The hydroxide ion (OH-) will increase the concentration of hydroxide in the solution, resulting in a basic pH.
To calculate the pH at the equivalence point, we need to know the concentration of the hydroxide ion (OH-) in the final solution. This can be calculated using the overall balanced equation for the hydrolysis reaction and a simple ICE table.
In this case, the concentration of hydroxide (OH-) is equal to the concentration of NaOH that was added, as the reaction ratio is 1:1.
Concentration of OH- = concentration of NaOH = 0.500 M
To find the pOH at the equivalence point, we can use the equation:
pOH = -log10(concentration of OH-)
pOH = -log10(0.500)
pOH ≈ 0.301
From the pOH, we can calculate the pH using the equation:
pH = 14 - pOH
pH = 14 - 0.301
pH ≈ 13.699
Therefore, the pH at the equivalence point is approximately 13.699.