Determination of the Solubility Product Constant for Calcium Hydroxide

SCH4UName: /40 Determination of the Solubility Product Constant for Calcium Hydroxide

The solution process can be considered as an equilibrium process and as a result, an equilibrium constant can be assigned. It is given a special designation, Ksp.

In this investigation, you will determine the value of the Ksp for calcium hydroxide. You will be given a saturated solution of calcium hydroxide with an excess of crystals on the bottom. The solution will be at room temperature. To calculate the Ksp value, the concentration of hydroxide ions and calcium ions in the equilibrium solution are needed. The [OH-] will be found by titrating a sample of the saturated solution with acid of known concentration.

Pre-lab

1. Write an introduction for this lab, as if you were writing a formal lab report. You MUST have references and they MUST be written in APA format. [ /5]

2. Make a check-list for this lab. Make sure that each term in the check-list has only ONE task.

3. Make a chemical safety table for all the chemicals used in this experiment. Refer to the Esters lab for an example. [ /2]

4. Find the Ksp value for Ca(OH)2 [ /1]

Materials

Burette Pipette SCH4UName: /40 Distilled water Saturated calcium hydroxide solution

Pipette bulb Methyl orange indicator

Erlenmeyer flasks 0.05 M HCl

Procedure

1. The saturated solution of calcium hydroxide has already been prepared for you. It has been “equilibrating” for at least six days

2. Prepare a 50 mL burette for titration. Rinse the clean burette and tip with 5 mL portions of standardized 0.05 M HCl solution and discard the washing. Repeat this procedure again.

3. Fill the burette with HCl and record the initial volume

4. Try to keep the undissolved calcium hydroxide so that it remains on the bottom of the flask. With minimum disturbance, carefully decant the saturated solution into a second flask. Take approximately 50 mL of saturated solution

5. Record the temperature of the sample taken

6. Rinse the 10 mL pipette with 2 mL of the saturated hydroxide solution and discard. Pipette 10 mL of the saturated hydroxide solution into another clean Erlenmeyer flask. Add two drops of methyl orange indicator

7. Titrate with the standard 0.05 M hydrochloric acid solution. Record the volume needed to just turn the yellow colour to a permanent pink.

8. Repeat the process until the numbers are within 0.2 mL

9. All waste is to be discarded in the container provided for this purpose.

Questions

1. Calculate the moles of acid used in the titration [ /3] SCH4UName: /40

2. From a balanced chemical equation for the titration reaction, determine the moles of OH- ion used in the reaction [ /2]

3. Calculate the concentration of OH- ions and Ca2+ ions in the saturated solution, in mol/L

4. Why does the reactant not appear in the equilibrium law for this equilibrium? [ /1]

5. Calculate the value of Ksp for Ca(OH)2 [ /6]

6. 200 mL of 1.500 M CaI2 was added to 100.0 mL of the saturated Ca(OH)2 solution. Calculate the equilibrium concentration of the OH- ion [ /4]

Lab Skills

- All equipment was used properly

- All chemicals were used and disposed of properly

- The lab area was cleaned properly

- The results were accurate