Some chemicals are acids or alkalis. Vinegar, lemon juice and sour milk are all weak acids. They all have a similar sharp, sour taste. Oven cleaner, washing soda and toothpaste are all alkalis. Alkalis taste bitter and feel soapy.
Our stomachs contain hydrochloric acid. This acid kills some of the bacteria in our food and helps us to digest our meals. Too much stomach acid causes indigestion. Medicines used to cure stomach pains are often alkalis. When you mix an alkali with an acid, you make a ‘neutral’ solution — neither acidic nor alkaline. Many plants thrive in a soil which is not very acid, so farmers may add lime to the soil. Lime (an alkali) ‘neutralizes’ acidic soil.
Indicators
An ‘indicator’, such as litmus, is a substance that changes colour when it is mixed with an acid or an alkali.
When litmus paper is dipped into lemon juice, it turns red. Alkaline stomach medicine turns it blue. When the acid and the alkali are mixed, a neutral solution is formed which does not colour the litmus.
Car batteries contain a very strong acid solution. Never touch a car battery with bare fingers.
Farmers and gardeners use an alkali – lime – to neutralize acidic soil before planting.
Picture Credit : Google