Bases

Bases are the chemical opposites of acids. Strong bases are corrosive substances with a greasy slippery feel.

Bases contain ions that can neutralise (react with and cancel out) the H+ ions of the acids, such as the hydroxide ion, the oxide ion and the carbonate ion.

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Neutralisation

Just as acids neutralise bases, so bases neutralise acids by reacting with the H⁺ ions of the acidic solution. In all neutralisation reactions water is formed:

Base	neutralisation
hydroxide	OH- + H+ H2O
oxide	O2- + 2H+ H2O
carbonate	CO32- + 2H+ H2O + CO2
hydrogen carbonate	HCO3- + H+ H2O + CO2
sulfate(IV)	SO32- + 2H+ H2O + SO2

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Alkalis

Alkali is simply the term given to a soluble base, such as sodium hydroxide, potassium hydroxide or barium hydroxide.

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Ammonia

Ammonia has the molecular formula NH₃. It is a pungent (sharp) smelling gas that is used in household cleaners. It is very soluble in water giving a solution of about pH 10.

Ammonia gas dissolves in water to give a solution that behaves as a base in that it neutralises acids producing a salt and water. The reason for this is that the ammonia molecule partially removes some of the hydrogen ions from water leaving the solution with an excess of OH´(hydroxide ) ions. These ions can then react with acids.

ammonia	+	water		ammonium ions	+	hydroxide ions
NH3		H2O		NH4+		OH-

This equilibrium reaction lies very much to the left hand side, meaning that there is much more of the molecular form of ammonia in the solution than there is of the ions.

However, any reaction of the hydroxide ions removes them from the equilibrium which responds (Le Chatelier, take from the right hand side, make more of the right hand side) by making more. Thus, any reaction which neutralises the OH^- ions goes all the way to completion.

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Ammonia reactions

sulfuric acid	+	ammonia		ammonium sulfate
H2SO4		2NH3		(NH4)2SO4
hydrochloric acid	+	ammonia		ammonium chloride
HCl		NH3		NH4Cl
nitric acid	+	ammonia		ammonium nitrate
HNO3		NH3		NH4NO3
ethanoic acid	+	ammonia		ammonium ethanoate
CH3COOH		NH3		CH3COONH4

Note: There is no water formed in the reaction. Some textbooks refer to a solution of ammonia in water as 'ammonium hydroxide' solution, NH₄OH, in which case there will be water formed when it reacts with acids.

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Indicators

Indicators may be used to test for bases in the same way as they are used to test for acids (only with different colours of course)

Common indicator colour changes are:

Bases register values from 7 (neutral) to 14 on the pH scale.

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