Types of Compounds Acids, Bases and Indicators

  • Any compound can be classified based on its chemical properties
  • On the basis of their chemical properties, all the compounds can be classified into three groups :
  •  Acids,
  •  Bases, and
  •  Salts
  • An indicator is used to detect the chemical properties of that compound
  • Natural Indicator
  • Turmeric is also a natural indicator
  • The red cabbage extract (obtained from red cabbage leaves) is also a natural indicator
  • The red cabbage extract remains red in acidic solutions but turns green on adding to basic solutions
  • The flowers of Hydrangea plant are usually blue which turn pink in the presence of a base.
  • The three most common indicators to test for acids and bases are : Litmus, Methyl orange and Phenolphthalein
  • Litmus PaperLitmus is a natural indicator (whose neutral colour is purple).
  • Litmus is a natural indicator
  • Litmus Is obtained from Lichen a plant from thallophyte
  • An acid turns blue litmus to red.
  • A base (or alkali) turns red litmus to blue
  • The neutral colour of methyl orange is ‘orange
  •  Methyl orange indicator gives red colour in acid solution.
  •  Methyl orange indicator gives yellow colour in basic solution
  • The neutral colour of phenolphthalein is ‘colourless’.
  • Phenolphthalein indicator is colourless in acid solution.
  •  Phenolphthalein indicator gives pink colour in basic solution
use of litmus paper to detect acid and base
use of litmus paper to detect acid and base
  • Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators
  • Exampls – Onion , vanilla, Clove
  • Onion ,Vanilla Loose its smell when it is added to a base like NaOH ,And does not loose its smell when added to a acid like HCL
examples of olfactory indicators
examples of olfactory indicators
  • You have been provided with three test-tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test-tube ?
  • Acid : An acid is a substance which dissociates (or ionises) on dissolving in water to produce hydrogen ions [H+(aq) ions
  • Acids Do Not Show Acidic Behaviour in the Absence of Water
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