Sulfuric acid

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Sulfuric acid (also spelled sulphuric acid or in old texts as oil of vitriol) is one of the strong mineral acids and has a number of practical uses in refining. The acid differs from hydrocloric acid and nitric acid in that it contains two hydrogen atoms that can be ionized in water. This means that concentrated sulfuric acid and diluted can appear as two different acids.

Strong sulfuric acid is is so powerful that it will rob hydrocarbons of the water in the molecules, leaving carbon as a byproduct. A famous experiment is to add sulfuric acid to sugar and getting a pillar of carbon.

WARNING!

Do not pour water into concentrated sulfuric acid when diluting. Always pour sulfuric acid in water and use protective gear.

If water is poured into concentrated sulfuric acid it will turn to steam and can create a steam explosion, throwing acid out of the vessel.

Dilution of acids

Contents

Uses in refining

Removing lead in solution

When dissolving gold in aqua regia any lead will also dissolve. Some of the lead chloride will dissolve and follow the gold chloride through filters. If some sulfuric acid is added to the gold chloride the lead will form unsoluble lead sulfate and precipitate. It can be filtered off from the gold chloride and leave the gold virtually lead free. Traces of lead in gold will make it brittle and impossible to work with.

It will also make it easier to denox the solution by evaporation.

Making copperas for precipitating gold

Copperas is used to precipita te gold from gold chloride. It is easy to make from soft iron and sulfuric acid.

Inquarting gold with silver

If gold is inquarted with silver, the silver can be removed with hot sulfuric acid as long as the copper level is under 10%.

Reverse plating cell

(Main article : Reverse plating cell)

An electrical cell with concentrated sulfuric acid (>90%) as electrolyte can dissolve gold from base metals without attacking the base metal. The gold is recovered as a black sludge at the end of the run.

Converting silver chloride to metal

(Main article : Silver chloride conversion with sulfuric acid)

One way to convert silver chloride back into metal is with weak sulfuric acid and some iron, zinc or aluminum.

Rhodium refining

(Main article : Rhodium refining)

Rhodium can be dissolved in hot concentrated sulfuric acid.

Making nitric acid

Sulfuric acid can be used for making "homemade nitric acid". The principle is that mixing sulfuric acid with a nitrate salt, the resulting mix will contain nitric acid. If the nitrate salt corresponds to a low solubility sulfate salt then the sulfate will precipitate and nitric acid will remain. As there will be traces of sulfate in the nitric acid it is unsuitable for working with silver unless the nitric acid is purified by distillation.

Sources

  • Some brands of drain cleaner is almost pure sulfuric acid.
  • Battery acid is diluted sulfuric acid. It can be concentrated by evaporating the water off by heating.

Distilling sulfuric acid

If you have contaminated or weak sulfuric acid the acid can be brought back to a pure concentrated state by distilling. Be aware that hot concentrated sulfuric acid is very dangerous.

Making sulfuric acid

There are several ways that a weak sulfuric acid can be made. One easy and quite cheap way is by electrolysis of copper sulfate.

References

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