Ksp of calcium hydroxide

[Guest dolphinlovr22]

I did an experiment in my chem 2 class for college. We had to titrate calcium hydroxide using HCl. After we found the volume and calculated the moles, concentrations, etc, we had to calculate the Ksp of the calcium hydroxide solution. Our percent error was really high and our prof. said that is what we have to try to figure out. Basically, I am asking why the percent error of Ksp would be so high in a calcium hydroxide titration. THANKS!

[fafalone]

Did you overshoot the equivalence point and not back-titrate?

[wolfson]

The inaccuracy is more likely to occur with salts that are fairly soluble. The reason is the assumptions made in the Ksp model (that interactions between water molecules themselves and between water molecules and ions are of roughly the same strength; that the water molecules are 100% effective in decreasing the attraction of positive ions for negative ions). In fact, especially with fairly soluble salts, ion pairs form (ion pairs are not true molecules but ions which are moving together because of the attractions of opposite charges). When Ksp is large that means that the reaction favors the dissociated. More dissolved in. When Ksp is small that means that the reaction favors the non-dissociated part of the equation.

 

(APP 2002 & Chem 7's 2nd ed 2004)

[wolfson]

Dolphinlovr22, if you want you can show me all the calculations and equations you used, and i could see if there was a problem there, but the most likley is posted above. Welcome to the SFN