K2CO3
DEFINITION
Content: 99.0 per cent to 101.0 per cent (dried substance).
CHARACTERS
Appearance: White or almost white granular powder, hygroscopic.
Solubility: Freely soluble in water, practically insoluble in ethanol (96 per
cent).
IDENTIFICATION
A. Dissolve 1 g in 10 ml of water. The solution is strongly alkaline.
B. 2 ml of the solution prepared for identification test A gives the reaction of
carbonates and bicarbonates.
C. 1 ml of the solution prepared for identification test A gives reaction of
potassium.
TESTS
Solution S: Dissolve 10.0 g in 25 ml of distilled water. Slowly add 14 ml of
hydrochloric acid. When the effervescence has ceased, boil for a few minutes. Allow
to cool and dilute to 50 ml with distilled water.
Appearance of solution: Solution S is not more opalescent than reference
suspension and not more intensely coloured than reference solution.
Chlorides: Maximum 100 ppm.
Sulphates: Maximum 100 ppm.
Calcium: Maximum 100 ppm.
Iron: Maximum 10 ppm.
Heavy metals: Maximum 20 ppm.
Loss on drying: Maximum 5.0 per cent, determined on 0.300 g by drying in an
oven at 120-125°C for 5 h.
ASSAY
Dissolve 0.500 g in 50 ml of carbon dioxide-free water. Carry out a potentiometric
titration, using 1 M hydrochloric acid . Read the volume added at the 2nd point of
inflexion.
1 ml of 1 M hydrochloric acid is equivalent to 69.1 mg of K2CO3.
K2CO3 (anhydrous) 138.21
Carbonic acid, dipotassium salt.
Dipotassium carbonate [584-08-7].
Sesquihydrate 165.23
Potassium Carbonate contains not less than 99.5 percent and not more than 100.5 percent of K2CO3, calculated on the dried basis.
Identification: It responds to the tests for Potassium and for Carbonate.
Loss on drying: Dry it at 180 for 4 hours: it loses not more than 0.5% of its
weight.
Insoluble substances: Dissolve 1 g in 20 mL of water: the solution is
complete, clear, and colorless.
Heavy metals: Dissolve 4.0 g in 10 mL of water, add 15 mL of 3 N hydrochloric
acid, and heat to boiling. Add 1 drop of phenolphthalein TS, and neutralize with 1 N
sodium hydroxide until the solution is faintly pink in color. Cool, and dilute with
water to 25 mL: the limit is 0.0005%.
Assay: Transfer the dried potassium carbonate obtained in the test for Loss
on drying to a flask with the aid of 150 mL of water, add 4 drops of methyl orange
TS, and titrate with 1 N hydrochloric acid VS. Each mL of 1 N hydrochloric acid is
equivalent to 69.11 mg of K2CO3.
K2CO3 Formula wt, anhydrous 138.21
K2CO3·1½H2O Formula wt, hydrated 165.23
INS: 501(i) CAS: [584-08-7]
DESCRIPTION
Potassium Carbonate is anhydrous or contains 1.5 molecules of water of
crystallization. The anhydrous form occurs as a white, granular powder, and the
hydrated form as small, white, translucent crystals or granules. It is very
deliquescent, and its solutions are alkaline. One gram dissolves in 1 mL of water at
25° and in about 0.7 mL of boiling water. It is insoluble in alcohol.
Function: pH control.
REQUIREMENTS
Identification: A 1:10 aqueous solution gives positive tests for Potassium
and for Carbonate.
Assay: Not less than 99.0% and not more than 100.5% of K2CO3 after
drying.
Insoluble Substances: Passes test.
Lead: Not more than 2 mg/kg.
Loss on Drying Anhydrous: Not more than 1%; Hydrated: Between 10.0% and
16.5%.
K2CO3
Formula Wt 138.21
CAS Number 584-08-7
REQUIREMENTS
Assay: 99.0% K2CO3 min
MAXIMUM ALLOWABLE
Insoluble matter: 0.01%
Chloride (as Cl): 0.003%
Nitrogen compounds (as N): 0.001%
Phosphate (PO4): 0.001%
Silica (SiO2): 0.005%
Sulfur compounds (as SO4): 0.004%
Ammonium hydroxide precipitate: 0.01%
Heavy metals (as Pb): 5 ppm
Iron (Fe): 5 ppm
Calcium: 0.005%
Magnesium: 0.002%
Sodium (Na): 0.02%
