Sulfuric Acid

Sulfuric Acid Sulphuric acid; H₂SO₄ = 98.08 (7664-93-9)

Content, 95.0% m/m to 97.0% m/m.

Colourless, caustic liquid with an oily consistency, highly hygroscopic, miscible with water and with ethanol (96%) producing intense heat.

, 1.834 to 1.837.

A 10 g/L solution is strongly acid and gives the reactions of sulfates (2.3.1).

Appearance It is clear (2.2.1) and colourless (2.2.2, Method II).

Oxidisable substances Pour 20 g cautiously, with cooling, into 40 mL of water. Add 0.5 mL of 0.002 M potassium permanganate. The violet colour persists for at least 5 minutes.

Chlorides Maximum 0.5 ppm.

Pour 10 g, carefully and while cooling, into 10 mL of water and after cooling dilute to 20 mL with the same solvent. Add 0.5 mL of silver nitrate solution R2. Allow to stand for 2 minutes protected from bright light. The solution is not more opalescent than a standard prepared at the same time using a mixture of 1 mL of chloride standard solution (5 ppm Cl), 19 mL of water and 0.5 mL of silver nitrate solution R2.

Nitrates Maximum 0.5 ppm.

Pour 50 g or 27.2 mL, carefully and while cooling, into 15 mL of water. Add 0.2 mL of a freshly prepared 50 g/L solution of brucine in glacial acetic acid. After 5 min any colour is less intense than that of a reference mixture prepared in the same manner and containing 12.5 mL of water, 50 g of nitrogen-free sulfuric acid, 2.5 mL of nitrate standard solution (10 ppm NO₃) and 0.2 mL of a 50 g/L solution of brucine in glacial acetic acid.

Ammonium Maximum 2 ppm.

Pour 2.5 g, carefully and while cooling, into water and dilute to 20 mL with the same solvent. Cool, and add dropwise 10 mL of a 200 g/L solution of sodium hydroxide, followed by 1 mL of alkaline potassium tetraiodomercurate solution. The colour of the solution is less intense than that of a mixture of 5 mL of ammonium standard solution (1 ppm NH₄), 15 mL of water, 10 mL of a 200 g/L solution of sodium hydroxide and 1 mL of alkaline potassium tetraiodomercurate solution.

Arsenic (2.4.2, Method A) Maximum 0.02 ppm.

To 50 g add 3 mL of nitric acid and evaporate carefully until the volume is reduced to about 10 mL. Cool, add to the residue 20 mL of water and concentrate to 5 mL. Prepare the standard using 1.0 mL of arsenic standard solution (1 ppm As).

Iron (2.4.9) Maximum 1 ppm.

Dissolve the residue on ignition with slight heating in 1 mL of dilute hydrochloric acid and dilute to 50.0 mL with water. Dilute 5 mL of this solution to 10 mL with water.

Heavy metals (2.4.8) Maximum 2 ppm.

Dilute 10 mL of the solution obtained in the test for iron to 20 mL with water. 12 mL of the solution complies with test A. Prepare the reference solution using lead standard solution (2 ppm Pb).

Residue on ignition Maximum 0.001%, determined on 100 g by evaporating cautiously in a small crucible over a naked flame and igniting the residue to redness.

Assay Weigh accurately a ground-glass-stoppered flask containing 30 mL of water, introduce 0.8 mL of the sulfuric acid, cool and weigh again. Titrate with 1 M sodium hydroxide, using 0.1 mL of methyl red solution as indicator.

1 mL of 1 M sodium hydroxide is equivalent to 49.04 mg of H₂SO₄.

Store in a ground-glass-stoppered container made of glass or other inert material.

When no molarity is indicated use analytical reagent grade of commerce containing about 96% w/w of sulfuric acid and about 18m in strength.

When solutions of molarity xm are required, they should be prepared by carefully adding 54x mL of sulfuric acid to an equal volume of water and diluting to 1000 mL with water.

When 'sulfuric acid' is followed by a percentage figure, an instruction to add, carefully, sulfuric acid to water to produce the specified percentage v/v (or, if required, w/w) proportion of sulfuric acid is implied.