A 50.0 mL sample of 0.51 M benzoic acid, C6H5COOH, a weak monoprotic acid, is titrated with 0.40 M NaOH. Calculate the pH at the equivalence point. Ka of C6H5COOH = 6.5 10-5.
what am i supposed to do with this?
The pH at the equivalence point is determined by the hydrolysis of the salt, in this case, sodium benzoate.
C6H5COO^- + HOH ==>C6H5COOH + OH^-
Now, write the Keq expression, set up an ICE chart, and solve for OH^-. Then change to pOH, then to pH. Post your work if you get stuck. Kb for the base (the C6H5COO^-) is Kw/Ka.
Idek hehe
To calculate the pH at the equivalence point of the titration, we need to determine the concentration of the benzoic acid at that point. The equivalence point occurs when the moles of acid equal the moles of base.
Here's how you can calculate the concentration of benzoic acid at the equivalence point:
1. Determine the moles of benzoic acid in the initial sample:
Moles = Concentration (M) x Volume (L)
Moles = 0.51 M x 0.050 L = 0.0255 moles
2. Determine the moles of NaOH needed to neutralize the benzoic acid:
Since 1 mole of benzoic acid reacts with 1 mole of NaOH, the moles of NaOH required will be the same as the moles of benzoic acid: 0.0255 moles.
3. Calculate the volume of NaOH required to reach the equivalence point:
Moles = Concentration (M) x Volume (L)
0.0255 moles = 0.40 M x Volume (L)
Volume (L) = 0.0255 moles / 0.40 M = 0.06375 L
4. At the equivalence point, the volume of NaOH added is equal to the total volume of the solution. So, the total volume at the equivalence point is 0.050 L + 0.06375 L = 0.11375 L
5. Calculate the concentration of benzoic acid at the equivalence point:
Concentration = Moles / Volume
Concentration = 0.0255 moles / 0.11375 L = 0.224 M
Now that we have the concentration of benzoic acid at the equivalence point, we can calculate the pH using the Ka value.
The Ka value of benzoic acid is given as 6.5 x 10^-5. The dissociation of benzoic acid can be represented by the equation:
C6H5COOH ⇌ C6H5COO- + H+
Since benzoic acid is a weak acid, we can assume that the concentration of benzoic acid at the equivalence point is fully dissociated into its conjugate base and hydronium ions.
6. Calculate the concentration of hydronium ions, [H+]:
[H+] = sqrt(Ka x Concentration)
[H+] = sqrt(6.5 x 10^-5 x 0.224)
[H+] = √(1.456 x 10^-5)
[H+] ≈ 1.21 x 10^-3 M
7. Calculate the pH using the concentration of hydronium ions:
pH = -log[H+]
pH = -log(1.21 x 10^-3)
pH ≈ 2.92
Therefore, the pH at the equivalence point of the titration is approximately 2.92.