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Chemistry-Topic 3 ((Indicator Acidic Neutral Alkaline, Litmus…
Chemistry-Topic 3
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Acid-alkali indicators can show whether a solution is acidic, neutral (pH 7) or alkaline.
The pH scale measures the acidity or alkalinity of a solution. The pH of a solution can be measured using a pH probe, or estimated using universal indicator and a colour chart.
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Reactions of acids
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Acids take part in reactions in which salts are produced. In these reactions, the salt is formed by replacing the hydrogen ions in the acids with metal ions or ammonium ions.
Neutralisation
Bases and alkalis
A base is any substance that reacts with an acid to form a salt and water only. This means that metal oxides and metal hydroxides are bases.
Bases that are soluble in water are called alkalis and they
dissolve in water to form alkaline solutions. For example:
copper oxide is a base, but it is not an alkali because it is insoluble in water
sodium hydroxide is a base, and it dissolves in water so it is also an alkali
Neutralisation reactions
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acids in solution are sources of hydrogen ions, H+
alkalis in solution are sources of hydroxide ions, OH-
In acid-alkali neutralisation reactions, hydrogen ions from the acid react with hydroxide ions from the alkali.
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Now remove the spectator ions, Cl-(aq) and Na+(aq). This leaves:
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Pure water is neutral (its pH is 7). A neutral solution can be produced if the correct amounts of acid and alkali react together. The change in pH during a neutralisation reaction can be measured using a pH probe and meter, or estimated using universal indicator solution and a pH colour chart.
