Acids and Bases - Key facts to learn

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acid

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A solution with a pH of less than 7 and that contains an excess of hydrogen (H+) ions.

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alkali

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A solution with a pH of more than 7 and that contains an excess of hydroxide (OH–) ions. A soluble base.

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aqueous solution (aq)

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A solution with water as the solvent.

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concentration

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A measure of how much solute is dissolved in a solvent such as water. (Units g dm-3 or mol dm-3)

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indicator

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A substance that changes colour depending on the pH of a solution.

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neutral

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A substance that is neither an acid nor an alkali. Neutral solutions have a pH of 7 and the same concentrations of hydrogen (H+) and (OH–) ions.

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pH scale

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A numerical scale up to 14 that measures the acidity or alkalinity of a solution based on the concentrations of hydrogen (H+) and (OH–) ions.

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universal indicator

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An indicator, containing a mixture of different pH indicators, designed to produce a range of colours depending on the pH.

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concentrated

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Containing a large amount of solute dissolved in a small volume of solvent.

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dilute

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Containing a small amount of solute dissolved in a large volume of solvent.