Precipitation - Water droplets falling as snow, rain, mist, hail or fog.
Acid Rain - precipitation that is more acidic that normal.
Acid - a hydrogen compound, turning Universal Indicator yellow, orange or red
Alkali - a soluble base, turning Universal Indicator blue or purple
Neutralisation - a reaction of an acid with a alkali forming a salt and water
Indicator - a dye that has different colours in acid and alkaline solutions
pH - a number that shows the strength of the acid or alkali. Also indicates neutral
Salt - a compound formed when a metal replaces the hydrogen in an acid