Sulfuric Acid

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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H₂SO₄ 98.08

Sulfuric acid CAS RN^®: 7664-93-9.

1 DEFINITION

Sulfuric Acid contains NLT 95.0% and NMT 98.0%, by weight, of sulfuric acid (H₂SO₄).

[CAUTION-When sulfuric acid is to be mixed with other liquids, always add it to the diluent, and exercise great caution.]

2 IDENTIFICATION

A. IDENTIFICATION TESTS-GENERAL, Sulfate (191): Meets the requirements

3 ASSAY

PROCEDURE

Sample solution: Place 1 mL of Sulfuric Acid in a weighed, glass-stoppered flask containing 20 mL of water, and weigh again to obtain the weight of the Sulfuric Acid. Dilute with 25 mL of water, and cool.

Titrimetric system

(See Titrimetry (541).)

Mode: Direct titration

Titrant: 1 N sodium hydroxide VS

Blank: 45 mL of water

Endpoint detection: Visual

Analysis: To the Sample solution add methyl orange TS, and titrate with 1 N sodium hydroxide VS. Perform a blank determination. Calculate the percentage of sulfuric acid (H₂SO₄) taken:

Result = {[(V_S − V_B) x N x F]/W} x 100

V_S = Titrant volume consumed by sulfuric acid in the Sample solution (mL)

V_B = Titrant volume consumed by the Blank (mL)

N = Titrant actual normality (mEq/mL)

F = equivalency factor, 49.04 mg/mEq

W = weight of sulfuric acid in the Sample solution (mg)

Acceptance criteria: 95.0% -98.0%

4 IMPURITIES

4.1 RESIDUE ON IGNITION (281)

Sample: 22 mL (40 g)

Analysis: Evaporate the Sample to dryness, and ignite.

Acceptance criteria: NMT 2 mg of residue remains (0.005%).

4.2 CHLORIDE AND SULFATE, Chloride (221)

A dilution of 1.1 mL (2.0 g) in water shows no more chloride than corresponds to 0.15 mL of 0.020 N hydrochloric acid (50 ppm).

Change to read:

4.3 ARSENIC (211), Procedures, Procedure 1 (CN 1-JUN-2023)

Test preparation: Add 1.6 mL (3.0 g) to a mixture of nitric acid and water (3:20). Evaporate the solution until dense fumes of sulfur trioxide form. Cool, and cautiously wash the solution into an arsine generating flask with 50 mL of water.

Analysis: Proceed as directed in the chapter, omitting the addition of the 20 mL of 7 N sulfuric acid.

Acceptance criteria: NMT 1 ppm

5 SPECIFIC TESTS

REDUCING SUBSTANCES

Sample: 4.4 mL (8.0 g)

Analysis: Carefully dilute the Sample with 50 mL of ice-cold water, keeping the solution cold during the addition. Add 0.10 mL of 0.10 N potassium permanganate.

Acceptance criteria: The solution remains pink for 5 min.

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers.