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Primary Standards used in Standardization of Volumetric Solutions

Learn how to use and dry the primary standards used in standardization of volumetric solutions.
These are materials which, after drying under the specified conditions, are recommended for use as primary standards in the standardization of volumetric solutions. The following are recommended for use as primary standards.
Arsenic Trioxide: Sublime arsenic trioxide in an appropriate apparatus and stored over silica gel.
Benzoic Acid: Sublimed benzoic acid in an appropriate apparatus and store in a tightly- closed container.
Potassium Bromate: Recrystallize potassium bromate from boiling water. Collect the crystals and dry to constant weight at 180°. Store in a tightly-closed container.
Potassium Dichromate: Heat potassium dichromate to 140° to 150° in an oven, cool in a desiccator and powder in a glass mortar.
Potassium Hydrogen Phthalate: Recrystallize potassium hydrogen phthalate from boiling water, collect the crystals at a temperature above 35°and dry to constant weight at 110°. Store in a tightly-closed container.
Potassium Iodate: Recrystallize potassium iodate from boiling water. Collect the crystals and dry to constant weight at 120°. Store in tightly-closed container.
Sodium Carbonate, Anhydrous: Filter at room temperature a saturated solution of sodium carbonate. Introduce slowly into the filtrate a stream of carbon dioxide, with constant cooling and stirring. After about 2 hours, collect the precipitate on a sintered glass filter. Wash the filter with ice-cold water saturated with carbon dioxide. After drying at 100° to 105°, heat to constant weight at 270° to 300°, stirring from time to time. Store in a tightly-closed container.
Sodium Chloride: To 1 volume of a saturated solution of sodium chloride add 2 volumes of hydrochloric acid. Collect the crystals formed and wash with hydrochloric acid. Remove the hydrochloric acid by heating on a water-bath and dry the crystals to constant weight at 300°. Store protected from moisture.
Sulphanilic Acid: Recrystallize sulphanilic acid from boiling water. Filter and dry to constant weight at 100° to 105°.
Zinc Granulated: Wash granulated zinc with dilute hydrochloric acid, followed by water, ethanol (95%) and finally acetone. Dry at 100° for 5 minutes and cool in a desiccator over silica gel.

Also see: SOP for Preparation and Standardisation of Volumetric Solution

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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