INFORMATION:

[HCl] = 0.1388 M
We placed 0.5 g Ca(OH)2 in 100 mL of the following solutions:
Flask A: Distilled Water (7.4 mL of HCl needed to titrate)
Flask B: 0.05 M NaOH (7.5 mL of HCl needed to titrate)
Flask C: 0.025 M NaOH (10.8 mL of HCl needed to titrate)
Flask D: 0.0125 M NaOH (8.9 mL of HCl needed to titrate)

QUESTION is to calculate the following for each flask:

[OH-]eq from titration data
[OH-]0 from original solution
[OH-] from Ca(OH2)
[Ca2+]eq from Ca(OH)2
Ksp = [Ca2+]eq * [OH-]eq

I got moles HCl by volume (L) * concentration (0.1388M)

Is the [OH-]eq the same as the moles of HCl?

Also a 25 ml aliquot was used.

No, the [OH-]eq is not the same as the moles of HCl. [OH-]eq represents the concentration of hydroxide ions at equilibrium, while moles of HCl represent the number of moles of hydrochloric acid used in the titration.

To calculate the [OH-]eq from the titration data, you need to consider the balanced chemical equation for the reaction between HCl and NaOH:

HCl + NaOH -> NaCl + H2O

Since the stoichiometry of the reaction is 1:1, the moles of HCl used in the titration will be equal to the moles of NaOH in the solution.

You mentioned that you calculated the moles of HCl by multiplying the volume (in L) by the concentration. To calculate the moles of NaOH, you can use the same approach by multiplying the volume of NaOH used in the titration (in L) by its concentration.

Once you have the moles of NaOH used in the titration, you can calculate the [OH-]eq by dividing the moles of NaOH by the total volume of the solution (in L). This will give you the concentration of hydroxide ions at equilibrium.

However, to calculate the [OH-]0 from the original solution, you need to consider the dilution that occurred when the Ca(OH)2 was added to the 100 mL of the solution. To do this, you can calculate the moles of Ca(OH)2 used by dividing its mass (in g) by its molar mass. Then, divide the moles of Ca(OH)2 by the total volume of the solution (in L) to obtain the concentration of hydroxide ions before any reaction occurred.

To calculate [OH-] from Ca(OH)2, you need to consider that each mole of Ca(OH)2 will react with two moles of OH- ions. So, to find the concentration of OH- from Ca(OH)2, divide the moles of Ca(OH)2 used (calculated earlier) by twice the total volume of the solution (in L).

To calculate [Ca2+]eq from Ca(OH)2, you need to consider that one mole of Ca(OH)2 produces one mole of Ca2+ ions. So, the concentration of Ca2+ ions at equilibrium is equal to the concentration of Ca(OH)2 used (calculated earlier) divided by the total volume of the solution (in L).

Finally, to calculate the Ksp value, multiply the [Ca2+]eq by the [OH-]eq obtained from the titration data.

Repeat the above steps for each flask (A, B, C, D) to calculate the requested values.