SCH4U
November 2014
LAB #___: Ksp of Ca(OH)2
Pre-lab Questions:
1. The Solubility of Ca(OH)2
Solid calcium hydroxide is added to water and mixed until it is saturated. Some solid calcium hydroxide
remains on the bottom of the flask it has been mixed in.
a) Write out the chemical equation that represents the equilibrium mixture.
b) What is the relationship between the concentration of calcium ions and hydroxide ions?
c) If you were told the concentration of hydroxide ions in this mixture how would this help you
determine the Ksp for calcium hydroxide?
d) Write out the equilibrium expression for calcium hydroxide.
2. Titration of calcium hydroxide
The easiest way to determine the concentration of a base is by titrating it with an acid of known
concentration.
a) Write out the chemical equation for the titration of calcium hydroxide with hydrochloric acid.
b) If 25.6 mL of 0.10M HCl(aq) is required to neutralize 10.0 mL of Ca(OH)2
i)
what is the concentration of Ca(OH)2?
ii)
What is the concentration of OH-?
iii)
What is the concentration of Ca2+?
LAB INSTRUCTIONS:
1. Titrate 10.0 mL of saturated calcium hydroxide with 0.020 M HCl using phenolphthalein as the
indicator.
2. Repeat the titrations until 3 trials are within 1 mL of each other. Record all data in the following
chart.
OBSERVATIONS:
Trial #
1
2
3
4
Initial buret reading
Final buret reading
Volume of HCl added
Average Volume:
Calculations:
1. Calculate the average volume of HCl required to neutralize calcium hydroxide.
2. Using this average volume and the balanced chemical equation, calculate the concentration of
calcium hydroxide in the saturated solution.
3. Using the concentration of calcium hydroxide, calculate the concentration of hydroxide and
then the calcium ion concentration in the saturated solution.
4. Create an ICE chart that reflects the solubility of calcium hydroxide. Calculate Ksp for calcium
hydroxide.
5. Look up the accepted value for Ksp for Ca(OH)2. Account for any discrepancies between your
value and the accepted value.