An indicator is a dye that changes colour when it is added into acid or base solutions an indicator gives different colours in acidic and basic solution. An indicator tells us whether the substance we are testing or analysing is acidic or basic by changing colour. There are three most common indicators to test for acids and bases they are

  1. Litmus paper
  2. Phenolphthalein
  3. Methyl orange

Litmus paper test

  1. An acid solution turns blue litmus to red
  2. A base solution turns red litmus to blue

Phenolphthalein

  • The neutral colour of Phenolphthalein is colourless
  • Phenolphthalein indicator is colourless in acids
  • Phenolphthalein gives pink colour with bases

Methyl orange

  1. The neutral colour of methyl orange is orange
  2. Methyl orange indicator gives red colour in acid solution
  3. Methyl orange indicator gives yellow colour in basic solution

About indicators:

  • Litmus is a natural indicator
  • It is extracted from a plant name lichen which belongs to the thallophyte family
  • In neutral status, litmus is purple in colour
  • Turmeric is also a natural indicator, it contains a yellow dye, it turns to red colour in basic solution (soap solution turns turmeric into the red due to the presence of a base)
  • Red cabbage extract is also a natural indicator it is red in colour, it shows red colour in acidic solution and turns green in a basic solution
  • There are certain coloured petals of flowers such as Hydrangea, petunia, geranium which changes their colour in the presence of acids and bases which are also known as indicators.
  • Hydrangea plants turn pink in basic soil and red in acidic soil
Lichen

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