How to Identify Calcium Hydroxide
Calcium hydroxide is a white powder with the chemical formula Ca(OH)2. Calcium hydroxide is also known as slaked or hydrated lime. Calcium hydroxide is used in metallurgy, in glass and paper manufacturing and for sewage wastewater treatment. In solution calcium hydroxide is very caustic and basic, with a pH above 12. The presence of calcium ions is usually detected using a chemical reaction with sodium carbonate: reaction Na2CO3 + Ca(OH)2 = CaCO3 + 2NaOH. White precipitant calcium carbonate (CaCO3) turns the solution milky.
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Things You'll Need
- Beaker, 25 ml
- Sodium carbonate solution, 5 to 10 percent
- Plastic pipette
Instructions
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1
Pour about 10 ml of the sample solution into the beaker.
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2
Cut a piece of pH paper about 1.5 inches long.
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3
Dip one end of the pH paper strip into the sample solution for 1 or 2 seconds, and take it out. The pH paper will change color.
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4
Compare the color of the pH paper with the pH scale typically printed on the pH paper pack and assign pH of the solution accordingly. If the sample solution's pH is 12 or higher, the sample is a hydroxide; proceed to the next step.
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5
Fill the plastic pipette with the sodium carbonate solution and add 1 to 3 mL of it to the beaker. If the solution in the beaker turns milky (due to the white precipitant), the sample compound is calcium hydroxide.
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Tips & Warnings
Calcium hydroxide can cause severe skin and eye irritations--always wear gloves and goggles when working with it.
