OCR AS Chemistry F332: Ions in Solids and Solutions

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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
The ions build up into a giant ionic lattice, in which very large numbers of ions are arranged
in fixed positions.
Cl- ion
Na+ ion
An example of a giant ionic lattice is sodium chloride, Na +Cl- (s).
In the sodium chloride lattice, each Na+ ion is surrounded by six Cl- ions, and each Cl- ion is
surrounded by six Na+ ions.
Each Na+ ion is attracted to the six Cl- round it, but repelled by other Na+ ions which are a bit
further away, and attracted to the next lot of Cl- ions which are further away still and so on.
It adds up to an infinite series of attractions and repulsions but overall the attractions are
stronger than the repulsions, which is why the lattice holds together.
It holds very strongly, which is why ionic solids are hard and have high melting and boiling
Sodium Chloride
Melting point High
Can conduct electricity when solid No
Can conduct electricity when molten liquid Yes
Can conduct electricity when dissolved in Yes

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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 in the same regular way as the ions.…read more

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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 water at random.
Now the Na+ and Cl- ions are separated they behave independently of each other.
Each ion solution is surrounded by water molecules.
Water is a polar molecule.…read more

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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 to form a solid, a precipitation reaction is said to have occurred.
If you add a solution of sodium chloride to silver nitrate solution, you get a white precipitate
of silver chloride.…read more

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Write an ionic equation for the reaction of barium chloride solution with sodium sulfate
A precipitation of barium sulfate is formed.…read more

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Sometimes, when solutions of ions are mixed, a covalent compound is formed.
This happens when an acid is neutralised by an alkali.…read more


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