Acids and alkalis

·         When we dissolve a substance in water we make an aqueous solution

·         A base is chemical which can neutralise acids

·         Alkalis are bases which can dissolve in water

·         Pure water is neutral

·         All acids are very sour

·         All acids form H+ ions when we add them to water

·         These hydrogen ions make the solution acidic

·         All alkalis form hydroxide (OH-) atoms when they are dissolved in water

·         These ions make the solution an alkaline

·         Indicators are special chemicals that change colours when added to an acid or alkali (litmus paper)

·         We compare the colour to the pH scale. The scale runs from 0 (most acidic) to 14 (most alkaline)

·         Universal indicator is a very special indicator which is made from a number of dyes

·         It turns a different colour at different values of pH

·         Anything in the middle of the pH scale (pH7) is neutral , neither acid nor alkali