Solubility Product of Ca(OH)2

Problem: Experimentally validate the solubility product of Ca(OH)2

Process: The value of Ksp is validated using titration – Volumetric experiment

Procedure: Prepare a saturated solution of Ca(OH)2 by dissolving CaO in water. Allow the liquid to settle overnight and filter the supernatant solution. The solution should be preferably kept in a container filled to the brim and closed never leave the solution exposed to air for long.(Why do we have to do it?)

Prepare a standard solution of HCl 0.05M. (If a standard solution is not given to you, you may have to prepare the solution and standardize it) – Today you are provided a standard solution.

Clean the following glassware needed for titration prior to starting the experiment, Burette, pipette – 10 mL, Erlenmeyer flask-100 – 200 mL. Proper rinsing is to be done – demonstrated.

The other equipments needed are burette stand, clamps etc. Set them up before filling the reagents.

Indicator that is to be used in this titration is phenolphthalein – add 2 drops to the appropriate reagent.

Pipette out 10 mL of calcium hydroxide into a clean Erlenmeyer flask, add 2 drops of the indicator, titrate it with the acid taken in the burette. The titration should be stopped at the end point. The end point is when the color changes form pale pink to clear by the addition of a single drop of acid from the burette. Proper techniques like washing down the flask with distilled water etc. are to be performed appropriately. During titration there should be proper swirling of the mixture to ensure uniform mixing of the liquids.The titration should be performed real quick once you obtain the Ca(OH)2 , do not leave the solution open for too long and exposed to the atmosphere.

For evaluation students are to show the pale pink color or the point prior to the end point to the teacher, the volumes of the solutions obtained should be attested by the teacher, this value should be used for calculation.

Students are to repeat the titration for concordant values (same value should be obtained at least twice – that would be your right volume of the acid consumed – do not average your readings)Once the titration is complete, wash glassware and put all equipments away and work on you calculations.

Calculate the Ksp, solubility product of CaOH2 and calculate the % error for the experiment by comparing it to the literature value for Ksp of CaOH2and include in your report.

Note: Experimental values for Ksp using this method gives a value between 3.5 E-5 to 4.0 E -5. This is a reasonable value. Probably if activity coefficients are used instead of molarity the values may be better.

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