What does the word ‘salt’ mean?

The word salt has two meanings in chemistry, a general meaning and a specific meaning.

General meaning
Salt = a chemical compound (made in a chemical reaction, for example, by reacting an acid with a base).

Specific meaning
Salt = sodium chloride (‘common salt’)

So, one way to make a salt is to react an acid with a base. The word equation for this is:
acid + base -> salt + water (general meaning of the word salt)

An example of this kind of reaction would be to react hydrochloric acid with sodium hydroxide:
hydrochloric acid + sodium hydroxide -> sodium chloride + water (and in this example the salt made is salt! So you could say the word salt has both the general and the specific meaning here. Two meanings in one go.)

At school, students often make salts by chemical reactions. And most of the salts featured in the June 2014 post are examples of salts commonly made by students. However, at GCSE level students are typically only required to learn the structure of one salt and the structure that they learn is that of salt (sodium chloride) itself.

Sodium chloride has a cubic structure.

Here is an animation illustrating the build up of a cubic structure from sodium ions, Na+ shown as yellow spheres and chloride ions, Cl shown as green spheres.

Building a sodium chloride crystal lattice

Building a sodium chloride crystal lattice

NaCl in 2D

NaCl in 2D

NaCl in 3D

NaCl in 3D

Our students also learn three other crystal structures at GCSE, but none of them are salts. They are the structures of diamond, quartz and graphite.

Can you identify the crystals in the two pictures below? One of them appears as golden cubes, but it is neither salt nor gold.

Quiz crystal 1

Quiz crystal 1

Quiz crystal 2

Quiz crystal 2

Third quiz question: what is the name of the type of reaction that takes place when an acid reacts with a base? Answers next post.


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