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What it is. This sulfuric acid solution is a 0.5 N (0.25 M) volumetric standard, supplied in a 1 L size. It is a clear, colorless acid titrant for determining bases, alkalinity, and nitrogen, and for acidifying samples and permanganate titrations.
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Normality versus molarity. Sulfuric acid releases two hydrogen ions per molecule, so its normality is twice its molarity. A 0.5 N solution is therefore 0.25 M, containing about 24.52 g of H2SO4 per liter, and each milliliter neutralizes 0.5 milliequivalent of base, equal to 20.00 mg of sodium hydroxide (calculated).
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A strong, non-oxidizing titrant at working strength. Dilute sulfuric acid behaves as a strong acid in titrations of bases. Unlike hydrochloric acid, it is not volatile, so standard solutions hold their strength well, and it is the preferred acid for permanganate titrations, where chloride would interfere.
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Kjeldahl and ammonia work. Standard sulfuric acid is used to trap distilled ammonia in Kjeldahl nitrogen methods or to back-titrate excess acid after distillation, giving total nitrogen in foods, feeds, soils, and waters.
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Calculating results. Base content equals the titrant volume in milliliters multiplied by the standardized normality and by the base's milliequivalent weight. For sodium hydroxide, each milliliter of 0.5 N sulfuric acid corresponds to 20.00 mg.
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Preparing working strengths. Diluting 200 mL of 0.5 N sulfuric acid to 1 liter gives 0.1 N, and 20 mL to 1 liter gives 0.01 N (calculated). Standardize each new working solution before critical use.
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Permanganate titrations. Permanganate and dichromate titrations require sulfuric acid, since hydrochloric acid can be oxidized and nitric acid is itself an oxidizer. A defined 0.5 N acid provides consistent acidity for those methods.
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Standardization. Verify concentration against a primary standard base such as dried sodium carbonate, using methyl orange or a mixed indicator, or against standardized sodium hydroxide with phenolphthalein.
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Where it is used. Laboratories use 0.5 N sulfuric acid for titrating bases and alkalinity, Kjeldahl nitrogen determinations, acidifying samples for permanganate and dichromate titrations, preparing weaker acid standards, and teaching titration.
Technical Specifications
| Chemical Name |
Sulfuric acid, aqueous solution |
| CAS Numbers |
7664-93-9 (sulfuric acid); 7732-18-5 (water) |
| EC Number (H2SO4) |
231-639-5 |
| Synonyms |
Oil of vitriol (concentrated), battery acid (dilute), H2SO4 solution |
| Formula (active) |
H2SO4 |
| Molecular Weight (active) |
98.08 g/mol |
| Equivalent Weight |
49.04 (diprotic; normal = 2 x molar) |
| Concentration |
0.5 N (0.25 M) |
| H2SO4 Content |
About 24.52 g/L (calculated) |
| Neutralizing Capacity |
1.00 mL = 0.5 meq; 20.00 mg NaOH (calculated) |
| Appearance |
Clear, colorless liquid |
| Physical State |
Liquid, aqueous solution |
| Exposure Limit (mist) |
OSHA PEL and NIOSH REL: 1 mg/m³ TWA |
| Package Size |
1 L |
Applications / Common Uses
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Base titration: Titrates bases and alkaline samples.
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Kjeldahl nitrogen: Traps or back-titrates distilled ammonia.
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Permanganate methods: Supplies acidity without interfering ions.
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Alkalinity: Titrates carbonate and hydroxide alkalinity.
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Standard dilutions: Prepares weaker acid standards.
Storage, Handling & Shipping
Store tightly closed in a corrosives cabinet away from bases, reactive metals, organic materials, and water-reactive substances. When diluting, always add acid slowly to water, never water to acid, since dilution releases heat.
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Incompatible materials: Bases, reactive metals (release hydrogen), organic materials, oxidizers and reducers, and cyanides or sulfides.
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Exposure limit (sulfuric acid mist): OSHA PEL and NIOSH REL: 1 mg/m³ TWA.
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Spill response: Contain and neutralize with sodium bicarbonate or an acid spill kit, then rinse with water.
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First aid: Skin or eyes: flush with water for at least 15 minutes and seek medical attention.
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GHS signal word: Danger or Warning depending on concentration; .
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DOT / shipping: UN2796, Sulfuric acid, Class 8.
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