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Acids and Alkalis

Salts made from an Acid and a Base.

Metal oxides are bases. A base will neutralise an acid.
If the metal oxide dissolves in water
it forms hydroxide ions and is called an alkali.

Any chloride or sulfate can be safely made by reacting the
correct metal
oxide with hydrochloric acid to make the chloride
or sulfuric acid to make the sulfate.

This is the balanced chemical equation for the reaction of
sulfuric acid and iron oxide.

sulfuric acid  +  iron(II) oxide      arrow     iron(II) sulfate  +  water
  H2SO4(aq)   +      FeO(s)         arrow         FeSO4(aq)    +  H2O(l)

This is the balanced chemical equation for the reaction of
hydrochloric acid and copper oxide.

hydrochloric acid copper(II) oxide  arrow  copper(II) chloride  +  water
    2HCl(aq)              +           
CuO(s)      arrow          CuCl2(aq)       +   H2O(l)

The base can be added a little bit at a time to the acid
and it will dissolve to form the soluble salt.
When no more base dissolves, the acid has been neutralised.
The undissolved base can be removed from the solution by filtration.
Pure salt crystals can then be crystallised from the neutral solution.

You can also use a carbonate to make salts in the same way.

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