Gypsum (CaSO4.2H2O), also known as calcium sulfate dihydrate, is a mineral found as a bed, in association with sedimentary rocks. Solid calcium sulfate occurs naturally in three forms depending on the number of water molecules within the crystal structure: anhydrite (CaSO4), plaster of paris (CaSO4•½H2O) and gypsum (CaSO4•2H2O). Gypsum can be used as a plaster ingredient, a fertilizer, an ingredient to harden water and in traditional Chinese medicines. Gypsum has been used as a construction material since ancient times. In the laboratory, calcium sulfate is prepared by the action of sulfuric acid on calcium chloride, calcium carbonate or calcium oxide.
- Sulfuric acid
- Calcium hydroxide
- Sodium chloride
- PH electrode
- Thermometer
- Stirrer
- 4-neck flask
- Air oven
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Instructions
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1
Install a four-neck flask with a PH electrode, a thermometer and a stirrer. Add 0.3 molar of sulfuric acid at 100 degree reaction temperature, and stir the solution at 400 rotations per minute (rpm) for 10 to 20 minutes. You can observe on the PH indicator a value around 0.7 to 0.8 at this point.
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2
Add sodium chloride catalyst in the ration 0 to 20 percentage by weight of sulfuric acid. Twenty minutes later, charge calcium hydroxide slurry to this mixture. Gypsum forms in the solution as colorless or white precipitate.
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3
Filter gypsum by means of suction filtration. Since water is a byproduct of this reaction, dry the solid obtained in step 2 in an air oven at 100 degrees.