Orthophosphoric acid is a clear, colourless, odourless mineral acid with the chemical formula H3PO4 that is soluble in water at all concentrations. The most common commercial concentrations are 75% to 85% where it is a viscous, syrupy liquid.
Polyphosphoric acid refers to concentrated grades of phosphoric acid containing more than 95% H3PO4 . All grades of polyphosphoric acid are highly viscous, colourless or slightly tinted liquids.
Essentially liquified sulphur dioxide (SO2) kept under pressure, sulphur dioxide takes the form of a clear, colourless liquid with a suffocating odour. It is used as a bleaching and sterilising agent, a food preservative and an industrial chemical.
Oleum is a solution of sulphur trioxide in concentrated sulphuric acid. Used in the manufacture of mixed acids, detergents and for other industrial purposes, it takes the form of off‑white to grey or light brown, slightly turbid, oily, fuming liquid which may contain sediment.
Aluminium sulphate, Al2(SO4)3, is essentially an aqueous solution in the form of a reddish‑brown, slightly opalescent liquid. It is principally used for water treatment.
Sulphuric acid is a strong mineral acid that is soluble in water at all concentrations. A central substance in the chemical industry, it takes the form of a colourless to dark grey, light yellow or light purple, slightly turbid, oily, corrosive liquid. Principal uses for sulphuric acid include lead-acid batteries for vehicles, ore processing, fertiliser manufacturing, oil refining, wastewater processing and chemical synthesis.