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Physical & Chemical properties

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The majority of the available data on the physical and chemical properties of sulphuric acid is taken from public domain reviews including the OECD SIDS (2001) and the 1998 review by the UK Pesticides Safety Directorate. The physical and chemical properties of sulphuric acid are well characterised due to the extensive industrial use and are summarised in the table below.

Sulphuric acid is a strong mineral acid that has a high affinity for (and is miscible with) water. It dissociates in water to form sulphate and hydrogen (hydronium) ions. The dissolution and dissociation of sulphuric acid in water is strongly exothermic and occurs with a vigorous reaction.

While pure (100%) sulphuric acid can be manufactured, this material loses some SO3 and the stability of the 98% grade acid and below is much greater. Sulphuric acid (95-98%) is the most common form and is referred to as concentrated sulphuric acid.

A number of the physical and chemical properties of sulphuric aicd are highly influenced by its purity (water content). Waivers are proposed (based on the nature of the substance and its reactivity with water) for granulometry, partition coefficient and surface tension.



Substance type

Inorganic compound

Appearance/physical state/colour

Colourless to brown, viscous liquid.

Melting/freezing point

10.4 to 10.9°C (100% sulphuric acid)

-1.11 to 3.0°C (98% sulphuric acid)

-13.89 to -10°C (96% sulphuric acid)

7.56°C (83% sulphuric acid)

Boiling point (at 1013 hPa)

290°C (100% sulphuric acid)

310-335°C (98% sulphuric acid)

330°C (96% sulphuric acid)

360°C (77% sulphuric acid)

Density at 20°C

1.8144-1.8305 kg/L (90-100% sulphuric acid)

Particle size distribution

Not required for a liquid

Vapour pressure
at 148.5°C

130 Pa (97% sulphuric acid)

Vapour pressure
at 20°C

214 Pa (65% sulphuric acid)

6 Pa (90% sulphuric acid)

Partition Coefficient

Not relevant for ionisable substances

Water solubility at 20°C


Surface Tension at 25°C

Not expected to be surface active

Flash point


Self ignition temperature





Not expected to possess explosive properties.

Oxidising properties

Does not meet the criteria for classification as an oxidiser

Stability in organic solvents and identity of relevant degradation products

Not considered critical for an inorganic acid

Dissociation constant

pKa= 1.92


A viscosity of 22.5 cP (0.0025 PaS; 22.5 mPaS) is reported for 95% sulphuric acid at 20 degrees Celsius.