Ions are charged particlescharged particle: A particle that carries an electric charge. which are formed when atoms [atom: All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. ], or groups of atoms, lose or gain electrons [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ]. For the examination, you need to know which ions are produced by acids, and which are produced by alkalis. You will also need to know the ionic equation for neutralisationneutralisation: Neutralisation is the reaction between an acid and a base to form a salt plus water..
State symbols are used in symbol equations:
- (s) means solid
- (l) means liquid (not the same as dissolved in water - see below)
- (g) means gas
- (aq) means aqueous (dissolved in water)
When acids dissolve in water they produce aqueous hydrogen ions, H+(aq). For example, looking at hydrochloric acid:
HCl(aq) → H+(aq) + Cl–(aq)
When alkalis dissolve in water they produce aqueous hydroxide ions, OH–(aq). For example, looking at sodium hydroxide:
NaOH(aq) → Na+(aq) + OH–(aq)
Ammonia is slightly different. This is the equation for ammonia in solution:
NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq)
Be careful to write OH– and not Oh– or oh–.
When the H+(aq) ions from an acid react with the OH–(aq) ions from an alkali, a neutralisation reaction occurs to form water. This is the equation for the reaction:
H+(aq) + OH–(aq) → H2O(l)
For example, hydrochloric acid and sodium hydroxide solution react together to form water and sodium chloride solution. The acid contains H+ ions and Cl– ions, and the alkali contains Na+ ions and OH– ions. The H+ ions and OH– ions produce the water, and the Na+ ions and Cl– ions produce the sodium chloride, NaCl(aq).
Back to Acid, bases and salts index
When an alkali is added to an acid, the pH of the mixture rises as the alkali reacts with it forming neutral products. An acid added to an alkali causes the pH to fall because the alkali is removed by reaction with the acid.
A reaction in which acidity or alkalinity is removed is called neutralisation. A neutralisation involving an acid and a base (or alkali) always produces salt and water (and nothing else).
Acid + base → salt + water
The name of the salt produced can be predicted.
If the acid is hydrochloric acid, the salt will be a chloride.
If the acid is nitric acid, the salt will be a nitrate.
If the acid is sulfuric acid, the salt will be a sulfate.
The first part of the name is always the metal that is part of the base.
|Acid||Base||Salt + water|
|hydrochloric acid||+ copper oxide||→ copper chloride + water|
|sulfuric acid||+ sodium hydroxide||→ sodium sulfate + water|
|nitric acid||+ calcium hydroxide||→ calcium nitrate + water|
Carbonates and acids
Carbonates also neutralise acids. As well as a salt and water, carbon dioxide is also produced. The name of the salt can be predicted in just the same way.
Potassium carbonate + hydrochloric acid → potassium chloride + water + carbon dioxide
The uses of sulfuric acid
Sulfuric acid is used to clean metal surfaces before they're painted. It's also an important starting material in the production of fertilisers and is used in car batteries.
Now try a Test Bite.
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