Given: Concentration of HCl is 0.1388M

0.5 g of Ca(OH)2 was placed in a flask. 100mL of 0.05M NaOH was poured into the flask. 25mL aliquot was filtrated and used for titration.
Suppose to calculate the OH^- equilibrium concentration from the titration data, as well as the OH^- from the original solution. Then calculate the OH^- from Ca(OH)2 and then calculate Ca^2+ from Ca(OH)2.

7.5mL of HCl was titrated for flask with 0.05M NaOH.