2.2 Acids, Bases and Salts

• Indicators are substances that change colour when they are added to acids and alkalis
• Litmus is the most well-known indicator. It turns red in acids and blue in
• Universal indicator is most commonly used in the laboratory. When added to a solution, it changes to a colour that shows the PH of the solution.
• Acids produce hydrogen ions, H+, when they dissolve in water, e.g. for hydrochloric acid
• A base is chemically opposite to an acid. A base that dissolves in water is called an alkali
• Alkalis produce hydroxide ions, OH-, when they dissolve in water, e.g. for sodium hydroxide
• Whilst some acids and alkalis are dangerous, others are in foods like vinegar or lemon juice. Those that are dangerous has the corrosive hazard warning symbol on their containers