CAS No.: 16731-55-8,
Molecular Weight: 222.3,
Chemical Formula: K2S2O5
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Potassium Metabisulfite
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Potassium
Metabisulphite BP
K2S2O5 - 222.3 - 16731-55-8DEFINITION
Potassium metabisulphite
(potassium disulphite).
Content
95.0 per cent to 101.0 per cent.
CHARACTERS
Appearance
White or almost white powder, or
colourless crystals.
Solubility
Freely soluble in water, slightly soluble in
ethanol (96 per cent).IDENTIFICATION
A. pH
(see Tests).
B.
To
5 ml of solution S (see Tests), add 0.5 ml of 0.05 M iodine. The
mixture is colourless and gives reaction of
sulphates.
C. Solution S gives reaction of
potassium.
TESTS
Solution S
Dissolve 5.0 g in
carbon dioxide-free water R and dilute to
100 ml with the same solvent.
Appearance of solution
Solution S is clear and colourless.
pH
3.0 to 4.5 for solution S.
Thiosulphates
To 2.00 g add 25 ml of a 42.5 g/l solution of
sodium hydroxide
and 75 ml of water. Shake until dissolved and add 10 ml of formaldehyde
and 10 ml of acetic acid. After 5 min, titrate
with 0.05 M iodine using 1 ml of starch solution. Carry
out a blank titration. The difference between the volumes consumed in
the 2 titrations is maximum 0.15 ml.
Iron
Maximum 10 ppm.
Selenium
Maximum 10 ppm.
Zinc
Maximum 25 ppm.
Heavy metals
Maximum 10 ppm.
Potassium Metabisulfite
USP
Potassium Metabisulfite
K2S2O5 222.33
Disulfurous
acid, dipotassium salt.
Dipotassium
pyrosulfite [16731-55-8].
Potassium
Metabisulfite
contains an amount of K2S2O5 equivalent to not less than 51.8 percent
and not more than 57.6 percent of SO2.
Identification—
A solution (1 in 20)
responds to the tests for Potassium and for Sulfite.
Iron— Dissolve 1.00 g in 14 mL of
dilute hydrochloric acid (2 in 7), and evaporate on a steam bath to
dryness. Dissolve the residue in 7 mL of
dilute hydrochloric acid (2 in 7), and again evaporate to dryness.
Dissolve the resulting residue in a mixture of 2 mL
of hydrochloric acid and 20 mL of water, add
3 drops of bromine TS, and boil to expel the bromine. Cool, and dilute
with water to 47 mL: the limit is 0.001%.
Heavy metals— Dissolve 2 g in 20
mL
of water, add 5 mL of hydrochloric acid,
evaporate on a steam bath to about 1 mL, and
dissolve the residue in 25 mL of water: the
limit is 0.001%.
Potassium Metabisulfite
FCC
Potassium Pyrosulfite
K2S2O5 Formula wt 222.31
INS: 224 CAS: [16731-55-8]
DESCRIPTION
Potassium
Metabisulfite occurs as white
or colorless, free flowing crystals,
crystalline powder, or granules. It gradually oxidizes in air to the
sulfate. It is soluble in water, but it is insoluble in alcohol. Its
solutions are acid to litmus.
Function: Preservative; antioxidant; bleaching agent.
REQUIREMENTS
Identification: A 1:10 aqueous solution gives positive tests for
Potassium and for Sulfite.
Assay: Not less than 90.0% of K2S2O5.
Lead: Not more than 2 mg/kg.
Iron: Not more than 10 mg/kg.
Selenium: Not more than 5 mg/kg.
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