A 20.00 ml sample of calcium hydroxide is titrated with 0.0100 M HCl until the color of the phenolphthalein indicator just disappears. The following readings were made on the buret: Initial reading = 2.77 ml Final reading = 30.23 ml What is the calculated Ksp of the calcium hydroxide?

Explanation:

We have to start with the ionization reaction of so:

Reaction 1

With this equation we can write the Ksp expression:

So, if we want to calculate the Ksp of we have to know the and concentrations. These concentrations can be calculate using the titration procedure. So, we have to start with the ionic reaction between HCl and Ca(OH)2, so:

 Reaction 2

Reaction 3

Reaction4

The volume of HCl used in the experiment is the substraction between the inital and final reading:

With this volume (27.46 mL = 0.02746 L) we can calculate the moles with the molarity equation, so:

The molar ratio between H+ and OH- is 1:1, therefore:

Finally we have to calculate the concentration of OH- using the volume (20 mL= 0.02 L) and moles of OH-

We already have the concentration of OH-the next step is the calculation of the concentration of . To do this, we have to use the molar ratio between and (reaction 1), the molar ratio is 1:2 therefore:

With these values now we can calculate the Ksp:

The Ksp value for the is