25.0 ml of a 0.100 M solution of the weak acid, CH3OOH is titrated with a 0.10 M solution of the strong base, NaOH. Calculate the pH of the equivalence point.

If 25.0 mL of 0.100 M soln is titrated with 0.10 M base, you know it will take 25.0 mL. So the salt at the equivalence point will be 0.05M (That's 0.025L x 0.1M to begin, you've added 0.025L so the concn is 0.025 x 0.1/0.050 = 0.05M) The pH at the equivalence point is determined by the hydrolysis of the salt. The salt is CH3COONa which I will call NaAc. It's the Ac^- that hydrolyzes.

..........Ac^- + HOH ==> HAc + OH^-
initial...0.05............0.....0
change....-x..............x......x
equil...0.05-x............x......x

Kb for Ac^- = (Kw/Ka for HAc) = (x)(x)/(0.05-x)
Solve for x, convert to pH.

To calculate the pH at the equivalence point, we need to determine the volume of the strong base, NaOH, needed to reach the equivalence point.

The balanced chemical equation for the neutralization of a weak acid (CH3OOH) with a strong base (NaOH) is as follows:

CH3OOH + NaOH -> CH3OO-Na+ + H2O

Since the reaction is 1:1, the volume of NaOH required to reach the equivalence point is equal to the volume of CH3OOH solution used, which is 25.0 mL.

Next, let's calculate the number of moles of CH3OOH in the solution:

moles of CH3OOH = volume (L) x concentration (M)
= 25.0 mL x (1 L / 1000 mL) x 0.100 M
= 0.0025 moles

Since the reaction is 1:1, the number of moles of NaOH required to neutralize 0.0025 moles of CH3OOH is also 0.0025 moles.

Now, let's calculate the volume of NaOH needed to reach the equivalence point:

volume (L) of NaOH = moles / concentration
= 0.0025 moles / 0.10 M
= 0.025 L
= 25.0 mL

Therefore, the volume of NaOH required to reach the equivalence point is also 25.0 mL.

At the equivalence point, all of the weak acid (CH3OOH) will be neutralized by the strong base (NaOH). This means that both the weak acid and its conjugate base will be present in solution.

The conjugate base of CH3OOH is CH3OO-Na+, which is a sodium salt of the weak acid. It is the conjugate base that will affect the pH of the solution at the equivalence point.

The pH at the equivalence point of a weak acid-strong base titration can be calculated using the following equation:

pH = pKa + log [conjugate base] / [weak acid]

The pKa value for CH3OOH can be found in a reference table or calculated using the Henderson-Hasselbalch equation.

Let's assume the pKa value for CH3OOH is 4.74.

Now, let's calculate the concentrations of the conjugate base (CH3OO-Na+) and the weak acid (CH3OOH) at the equivalence point.

Since we have 25.0 mL of 0.100 M CH3OOH solution, the initial moles of CH3OOH is:

moles of CH3OOH = volume (L) x concentration (M)
= 25.0 mL x (1 L / 1000 mL) x 0.100 M
= 0.0025 moles

Since the reaction is 1:1, the concentration of CH3OO-Na+ at the equivalence point is also 0.0025 M.

Using the equation:

pH = pKa + log [conjugate base] / [weak acid]
= 4.74 + log (0.0025 M) / (0.0025 M)

Calculating it, we get:

pH = 4.74 + log (1)
= 4.74 + 0
= 4.74

Therefore, the pH of the equivalence point in this titration is 4.74.