Ch – 5 Acids, Bases And Salts

  • 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.

Published by Priya Prakash

In the midst of winter, i found there was within me an invincible summer ~ Albert Camus

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