Chemical of the Week 12 – Sulfuric Acid


Sulfuric acid is referred to as the king of chemicals. It’s one of the first acids we meet in chemistry class.  156 Million tons are produced world wide annually and it is considered a barometer of industrial activity. It was called “oil of vitriol” by medieval European alchemists because it was prepared by roasting “green vitriol” -iron (II) sulfate. Today the industrial manufacture of sulfuric acid is by the Contact process, which is studied at GCSE ( unfortunately a list of  equations to memorise with a wee bit of Le Chatelier thrown in !) We use sulfuric acid in just about everything including batteries, paint, fertilizer, ore processing, paper processing, steel production and water treatment. Oh and don’t forget a more macabre use. The Mafia are quite fond of getting rid of corpses in vats of concentrated acid, but it seems this may just be the stuff of legend. Recent research suggest that the disappearance of a body in couple of minutes as reported by the Mafia informants just does not happen when scientists set up trials with pig carcasses.

Pure sulfuric acid is a colourless, odourless, oily liquid. It freezes at 10.5°C. When dilute it displays typical acid reactions but when concentrated it can act as a catalyst, an oxidising agent and a dehydrating agent- everyone loves the video clip of the dehydration of sugar. Concentrated sulfuric acid is 98% by weight as when it is distilled from an aqueous solution it forms an azeotrope (constant boiling mixture). An azeotrope is a mixture of two or more chemicals ( in this case sulfuric acid and water ) that cannot be separated by basic distillation processes because they share a common boiling point and vaporisation point. When diluting concentrated acid always remember acid to water – I do love a mnemonic “Always do things as you oughta, add the acid to the water, if you think your life’s too placid, add the water to the acid’


But why pick sulfuric acid this week ? Some fantastic photos have been taken recently on the Indonesian island of Java showing amazing jets of sulfuric acid being released from a volcano. Ijen is one of Indonesia’s most famous volcanoes and is of economic importance as it provides sulfur. Described as one of the worlds most dangerous jobs, miners access the crater in the middle of the volcano to access the deposits. Within the crater is a lake called Kawah Ijen that contains 600,000 tonnes of hydrogen chloride, 550,000 tonnes of sulfuric acid, 200,000 tonnes of aluminium sulphate and 170,000 tonnes of iron sulphate. Check out this website with some fantastic pictures of the lake.


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