Neutralisation
Bases and alkalis
A baseA substance that reacts with an acid to neutralise it and produce a salt. is any substance that reacts with an acidSubstance producing more hydrogen ions than hydroxide ions when dissolved in water. to form a saltThe substance formed when the hydrogen ion in an acid is replaced by a metal ion. and water only. This means that metal oxides and metal hydroxides are bases.
Some bases are solubleAble to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. in water. An alkaliSubstance producing more hydroxide ions than hydrogen ions when dissolved in water. is a soluble base - it dissolveWhen a substance breaks up and mixes completely with a solvent to produce a solution. in water to form an alkalineHaving a pH greater than 7. solutionMixture formed by a solute and a solvent.. For example:
- copper oxide is a base but it is not an alkali because it is insolubleUnable to dissolve in a particular solvent. For example, sand is insoluble in water. in water
- sodium hydroxide is a base and it dissolves in water, so it is also an alkali
Example
Explain why all alkalis are bases but not all bases are alkalis.
Alkalis are soluble bases, but only some bases are soluble in water, so these are not alkalis.
Neutralisation reactions
neutralisationThe reaction between an acid and a base to form a salt plus water. involves an acid reacting with a base or an alkali, forming a salt and water.
Reactions with metal oxides
In general:
acid + metal oxide 鈫 salt + water
For example:
sulfuric acid + copper(II) oxide 鈫 copper(II) sulfate + water
H2SO4(aq) + CuO(s) 鈫 CuSO4(aq) + H2O(l)
Reactions with metal hydroxides
In general:
acid + metal hydroxide 鈫 salt + water
For example:
nitric acid + sodium hydroxide 鈫 sodium nitrate + water
HNO3(aq) + NaOH(s) 鈫 NaNO3(aq) + H2O(l)
Aqueous neutralisation reactions
Remember:
- acids in solution form hydrogen ionElectrically charged particle, formed when an atom or molecule gains or loses electrons., H+
- solutions of alkalis contain hydroxide ions, OH-
Acid-alkali neutralisation reactions involve the reaction between hydrogen ions from the acid, and hydroxide ions from the alkali:
H+(aq) + OH-(aq) 鈫 H2O(l)
Pure water is neutralWhen a substance is neither acidic nor alkaline, and has a pH of 7. (its pHScale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline. is 7). A neutral solution can be produced if the correct amounts of acid and alkali react together.