The substances which taste sour are acidic in nature and they contain acids.
The word acid is derived from the Latin word “acere” which means sour.
The substances which taste bitter and are soapy in touch are basic in nature and they contain bases.
Special types of substances are used to test whether a substance is acidic or basic. These substances are known as indicators.
The indicators change their colour when added to a solution containing an acidic or a basic substance.
Some of the examples of acids are :
Acetic Acid – Vinegar
Formic Acid – Ant’s sting
Citric Acid – Citrus fruits
Lactic Acid – Curd
Oxalic Acid – Spinach
Ascorbic Acid – Amla, Citrus fruits
Tartaric Acid – Tamarind, Grapes, Unripe mangoes
Some of the examples of bases are :
Calcium hydroxide – Lime water
Ammonium hydroxide – Window cleaner
Sodium hydroxide / Potassium hydroxide – Soap
Magnesium hydroxide – Milk of Magnesia
The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. Eg: water, table salt, cooking oil, sugar solution.
Turmeric, litmus, china rose petals (Gudhal), etc., are some of the naturally occurring indicators.
The most commonly used natural indicator is litmus, which is extracted from lichens. It has a mauve (purple) colour in distilled water.
Litmus paper when added to an acidic solution, it turns red and when added to a basic solution, it turns blue.
Turmeric yellow colour in acidic and neutral substances while it turns bright red in basic substances.
China rose ( gudhal ) turns acidic solutions into dark pink ( magenta ) and basic solutions to green.
Phenolphthalein remains colourless in acidic solutions while it gives a pink colour in basic solutions.
The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
When an acid solution and a base solution are mixed in suitable amounts, both the acidic nature of the acid and the basic nature of the base are destroyed.
Accumulation of too much acidic substances cause indigestion, to neutralise this one can take an antacid such as milk of magnesia which contains magnesium hydroxide.
To neutralise formic acid released during an ant’s sting, one can rub baking soda ( sodium hydrogen carbonate ) or calamine solution which contains zinc carbonate.
To neutralise acidic soil, quick lime ( calcium oxide ) or slaked lime ( calcium hydroxide ) is added.
To neutralise basic soil, oraganic matter is added to it.
The factory wastes containing acidic substances are neutralised by adding basic substances.
The pollutants like carbon dioxide, nitrogen dioxide and sulphur dioxide mix with rain and forms acidic acid.
