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Ions in Solids and Solutions

Ionic Solids
In ionic solutions, ions are held together by their opposite electrical charges.

Each positive ion, called a cation, attracts several negative ions, called anions, and vice
versa.

The ions build up into a giant ionic lattice, in which very large numbers of ions…

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Hydrated Crystals
The crystals of some ionic solids include molecules of water.

For example, the formula of magnesium chloride crystals is MgCl 2·6H2O.

The water is not just mixed with the magnesium chloride crystals because this would just
make them damp.

Instead, the H2O molecules are fitted in the lattice…

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Ionic Substances in Solution
Many ionic substances dissolve readily in water.

When they do, the ions become surrounded by water molecules and spread out through
the water.



This illustrates this for sodium chloride




The dissolved ions, Na+ and Cl-, are no longer regularly arranged ­ they are scattered
through the…

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Ionic Equations
Ions in solutions behave independently ­ and this includes their chemical reactions.

The reactions of an ionic substance, such as sodium chloride, quite often involve only one of
the two types of ion ­ the other ion does not get involved in the reaction.

If two solutions react…

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Example
Write an ionic equation for the reaction of barium chloride solution with sodium sulfate
solution.

A precipitation of barium sulfate is formed.



Step 1: Write down symbols for the ions in each solution and the ions in the product

Ba2+ (aq) + 2Cl- (aq) + 2Na+ (aq) + SO42-…

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Neutralisation
Sometimes, when solutions of ions are mixed, a covalent compound is formed.

This happens when an acid is neutralised by an alkali.



For example, hydrochloric acid contains H+ (aq) and Cl- (aq), so we write:

H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq) Na+ (aq) +…

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