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How to Test for Calcium Hydroxide

Calcium hydroxide, commonly called slaked lime, is an inorganic compound with the chemical formula Ca(OH)2. This compound is a base and is widely used in industry--for example, as a cleaning agent. Identifying calcium hydroxide might be a chemistry class assignment that requires two tests. The first one measures the pH (acidity) of the calcium hydroxide solution to ensure it is basic. The second test, using a dilute solution of sulphuric acid, determines the presence of calcium ions.

Things You'll Need

Beaker
pH paper
Plastic pipette
Sulphuric acid solution (5 percent)

Instructions

- 1
  Pour about 5 milliliters of the solution to be tested into the beaker.
- 2
  Dip the strip of the pH paper strip into the solution and then take it out. The pH paper will change its color.
- 3
  Compare the color of the paper with the scale enclosed with the pH paper to assign the pH of the solution. A basic pH value such as 10 to 11 is indicative for calcium hydroxide.
- 4
  Fill a pipette with the sulphuric acid solution.
- 5
  Add five to ten drops of the solution from the pipette to the beaker.
- 6
  Observe the solution in the beaker: If a white precipitate forms, it indicates the presence of calcium ions; this reaction follows the equation Ca(OH)2 + H2SO4 = CaSO4 (precipitate) + 2H2O.

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