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When most people hear "salt," they think of seasoning or french fries. To a chemist, however, salt refers to an ionic compound created when an acid reacts with a base. As you might imagine, there are many different bases you could mix with hydrochloric or sulphuric acid, so there are many different salts you could produce. Some of these salts are common household and industrial products.
Sulphuric Acid Salts
Sulphuric acid is the most widely produced inorganic industrial chemical in the world. Its chemical formula is H2SO4, so when it reacts with a base like sodium hydroxide, it forms a salt called a sulphate, which contains the sulphate ion (SO4, with a charge of -2). There are many different sulphate salts. Combining sodium hydroxide with sulphuric acid, for example, produces sodium sulphate or sodium bisulfate. Potassium hydroxide and sulphuric acid yield potassium sulphate. Ammonia and sulphuric acid produce ammonium sulphate. Copper (II) oxide and sulphuric acid make copper (II) sulphate. Magnesium sulphate and calcium sulphate are common salts of sulphuric acid as well.
Hydrochloric Acid Salts
The salts of hydrochloric acid are numerous -- just as with sulphuric acid, you can probably find some of them around your home. The most common is sodium chloride -- table salt -- which is formed in the lab by combining sodium hydroxide with hydrochloric acid. Other common salts include calcium chloride, potassium chloride, magnesium chloride, lithium chloride, ammonium chloride and barium chloride; these can be produced from bases like calcium carbonate, potassium hydroxide, magnesium hydroxide, lithium hydroxide, ammonia and barium hydroxide, respectively.
Nature always prefers to go from stronger acid + stronger base ---> weaker acid + weaker base. Consequently, if you combine a strong acid with a weak base, you'll typically get an acidic salt, i.e., a salt that is weakly acidic. Mix hydrochloric acid (a strong acid) with ammonia (a weak base) and you get ammonium chloride, a weakly acidic salt. If you mix hydrochloric acid with sodium hydroxide (a strong base), by contrast, you get a neutral salt, NaCl, which does nothing to the pH of its solution. Adding hydrochloric acid to the weak base sodium bicarbonate, or baking soda, makes sodium chloride; it also makes carbonic acid, but because carbonic acid is in equilibrium with dissolved CO2, much of the excess carbonic acid breaks down into CO2 and bubbles out of the solution.
Applications of Common Salts
Calcium chloride is a popular de-icer for roads, sidewalks and driveways. Magnesium sulphate is available at your local supermarket, where you'll probably find it labelled as Epsom salt. Some sulphate salts find use as fertilisers, most notably potassium sulphate and ammonium sulphate; the latter is also useful in biochemistry as a way to precipitate proteins from a solution by increasing salt concentration. Potassium chloride is useful for making fertilisers and also for pharmaceuticals; its most unusual application is as a lethal injection in executions.
- Georgia State University: Common Salts
- "Chemical Principles, the Quest for Insight, 4th Edition"; Peter Atkins, et al.; 2008
- "Scientific American"; Bad Drugs: Lethal Injection Does Not Work as Designed; David Biello; April 2007
- ChemicalLand21: Potassium Chloride
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