Publication No. 12980
Determination of the Ksp of Ca(OH)2
Student Laboratory Kit
Materials Included In Kit
Calcium nitrate solution, Ca(NO3)2, 0.10 M, 250 mL
Sodium hydroxide solution, NaOH, 0.10 M, 250 mL
Pipets, Beral-type, with micro tips, 45
Plastic toothpicks, 30
Reaction strips, 12-well, 15
Additional Materials Required
Water, distilled, 250 mL
Beakers, 50-mL, 45
Paper, blank white, 15 sheets
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Reaction solutions may be disposed of according to Flinn Suggested Disposal Method #26b. Unused sodium hydroxide solution may be disposed of according to Flinn Suggested Disposal Method #10. The unused calcium nitrate solution may be disposed of according to Flinn Suggested Disposal Method #26b.
Answers to Prelab Questions
Calcium Ion Serial Dilutions
First well with no precipitation: Well 6
Concentration of Ca2+: 1.6 x 10–3 mol/L
Concentration of OH–: 5.0 x 10–2 mol/L
Ksp[Ca(OH)2]= 4.0 x 10–6 M3
Hydroxide Ion Serial Dilutions
First well with no precipitation: Well 4
Concentration of Ca2+: 5.0 x 10–2 mol/L
Concentration of OH–: 6.3 x 10–3 mol/L
Ksp[Ca(OH)2]= 2.0 x 10–6 M3
Answers to Questions
Determination of the Ksp of Ca(OH)2
This experiment uses microscale techniques to determine the solubility product, Ksp, of calcium hydroxide.
The solubility product constant, Ksp, is an equilibrium constant. The equilibrium is formed when an ionic solid dissolves in water to form a saturated solution. The equilibrium exists between the dissolved ions and the undissolved solid. A saturated solution contains the maximum concentration of ions of the substance that can dissolve at the temperature of the solution.
For any solid in equilibrium with its ions in solution the general chemical equation is
The equation for its solubility product constant, Ksp, is
For example, the equilibrium equation showing the ionic solid lead chloride dissolving in water is:
The solubility product expression is:
where square brackets refer to molar concentrations of the ions. A knowledge of the Ksp of a salt is useful, since it is used to determine the concentration of ions of the compound in a saturated solution. Understanding the maximum concentration is important to determine when a compound will precipitate out of solution and when it will stay in solution.
The solubility product to be determined in this experiment is that of calcium hydroxide, Ca(OH)2. Calcium hydroxide is a strong base, but is not very soluble in water.
This experiment uses a microscale technique to determine the solubility product of calcium hydroxide, Ca(OH)2. Serial dilutions of the solution of calcium nitrate are placed in separate wells of a reaction strip. The diluted solutions are combined with an equal volume of the sodium hydroxide solution. Calcium hydroxide precipitates in the wells where the concentrations of calcium and hydroxide ions exceed the solubility product. The first well where no precipitate is present is assumed to be a saturated solution, and the ion concentrations are used to calculate the solubility product. The process is repeated using serial dilutions of the sodium hydroxide solution and equal volumes of the 0.10 M calcium nitrate solution.
Calcium nitrate solution, Ca(NO3)2, 0.10 M, 10 mL
Sodium hydroxide solution, NaOH, 0.10 M, 10 mL
Water, distilled, 10 mL
Beakers, 50-mL, 3
Paper, blank, white, 1 sheet
Pipets, Beral-type, with micro tips, 3
Plastic toothpick, 2
Reaction strip, 12-well
Calcium nitrate solution is slightly toxic by ingestion. Sodium hydroxide solution is a corrosive liquid. Avoid contact with skin and especially the eyes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.
Part I. Prepare a series of diluted calcium ion solutions.
Part II. Precipitation reaction.
Part III. Check using serial dilutions of sodium hydroxide solution.
Student Worksheet PDF