(Ph. Eur. monograph 1078)
Ca(OH)2 74.1 1305-62-0
Preparation
Calcium Hydroxide Solution
DEFINITION
Content
95.0 per cent to 100.5 per cent.
CHARACTERS
Appearance
White or almost white, fine powder.
Solubility
Practically insoluble in water.
IDENTIFICATION
A. To 0.80 g in a mortar, add 10 mL of water R and 0.5 mL of phenolphthalein solution R and mix. The suspension turns red. On addition of 17.5 mL of a 103 g/L solution of hydrochloric acid R, the suspension becomes colourless without effervescing. The red colour occurs again when the mixture is triturated for 1 min. On addition of a further 6 mL of a 103 g/L solution of hydrochloric acid R and triturating, the solution becomes colourless.
B. Dissolve about 0.1 g in dilute hydrochloric acid R and dilute to 10 mL with water R. 5 mL of the solution give
reaction (b) of calcium (2.3.1).
TESTS
Matter insoluble in hydrochloric acid
Maximum 0.5 per cent.
Dissolve 2.0 g in 30 mL of hydrochloric acid R. Boil the solution and filter. Wash the residue with hot water R.
The residue weighs a maximum of 10 mg.
Carbonates
Maximum 5.0 per cent of CaCO3.
Add 5.0 mL of 1 M hydrochloric acid to the titrated solution obtained under Assay and titrate with 1 M sodium hydroxide using 0.5 mL of methyl orange solution R as indicator.
1 mL of 1 M hydrochloric acid is equivalent to 50.05 mg of CaCO3.
Chlorides (2.4.4)
Maximum 330 ppm.
Dissolve 0.30 g in a mixture of 2 mL of nitric acid R and 10 mL of water R and dilute to 30 mL with water R.
Sulfates (2.4.13)
Maximum 0.4 per cent.
Dissolve 0.15 g in a mixture of 5 mL of dilute hydrochloric acid R and 10 mL of distilled water R and dilute to 60 mL with distilled water R.
Elemental impurities
Any method that fulfils the requirements of general chapter 2.4.20. Determination of elemental impurities may be used.
| Element | Maximum content (ppm) |
| Cadmium | 1 |
| Lead | 1 |
Magnesium and alkali metals
Maximum 4.0 per cent, calculated as sulfates.
Dissolve 1.0 g in a mixture of 10 mL of hydrochloric acid R and 40 mL of water R. Boil and add 50 mL of a 63 g/L solution of oxalic acid R. Neutralise with ammonia R and dilute to 200 mL with water R. Allow to stand for 1 h and filter through a suitable filter. To 100 mL of the filtrate, add 0.5 mL of sulfuric acid R. Cautiously evaporate to dryness and ignite. The residue weighs a maximum of 20 mg.
ASSAY
To 1.500 g in a mortar, add 20-30 mL of water R and 0.5 mL of phenolphthalein solution R. Titrate with 1 M hydrochloric acid by triturating the substance until the red colour disappears. The final solution is used in the tests for carbonates.
1 mL of 1 M hydrochloric acid is equivalent to 37.05 mg of Ca(OH)2.
