Note on Indicators

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Indicators are the chemical substances which are used for identifying whether a given substance is acid or base. Indicators cannot take part in chemical reaction and do not affect the chemical reaction but show the end of the chemical reaction.

Litmus, phenolphthalein and methyl orange are the common indicators which determine the acidic and basic nature of a substance by a characteristic change in their colour. The ordinary indicators do not give information about the strength of acidic or basic substances. They show the following change of colour in acidic, alkaline and neutral solutions:

Common Indicators Acidic solution Alkaline solution Salt solution
Red litmus No change in colour Changes into blue colour No change in colour
Blue litmus Changes into red colour No change in colour No change in colour
Methyl orange Changes into red colour Changes into yellow colour Faint orange in colour
Phenolphthalein No change in colour Changes into pink colour No change in colour
Red cabbage juice Changes into red colour Changes into green colour Changes into faint purple colour

Universal indicator is a mixture of simple indicators. It is used for identifying the acidic and basic characters of substances and also indicates the strength of acidic and basic characteristic of substances. It is prepared by the combination of common indicators found in green blue solution or yellow litmus paper. In universal indicator, red or intense red colour indicates acidic nature while light blue or intense blue colour indicates alkaline nature.

Differences between ordinary indicator and universal indicator

Ordinary indicator Universal indicator
It is a weak organic substance made from lichens. It is a mixture of ordinary indicators.
It does not indicate the strength of acid and base. Example: Litmus paper. It indicates the strength of acid and base. Example: PH paper

  • Indicators are the chemical substances which are used for identifying whether a given substance is acid or base.
  • Litmus, phenolphthalein and methyl orange are the common indicators which determine the acidic and basic nature of a substance by a characteristic change in their colour.
  • The ordinary indicators do not give information about the strength of acidic or basic substances.
  • Universal indicator is used for identifying the acidic and basic characters of substances and also indicates the strength of acidic and basic characteristic of substances.
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Very Short Questions

An indicator is a chemical substance that has a capacity to show the termination of a chemical reaction by changing its color without taking part in chemical reaction.

The ordinary indicator indicate the substance as acid or base or salt but cannot meaure its strength while the universal indicator indicate any substance an acid or base and can determine its strength.

Universal indicator is a mixture of ordinary indicators. It can be used to find out pH of any solution along with its acidic and basic characters. But the ordinary indicator like litmus can be used just to find out whether the solution is acidic or basic. So, universal indicator is more efficient than litmus paper.

Those chemical substance which can detect whether the given solution is acid or base or salt is called ordinary indicator.

Universal indicator is a mixture of ordinary indicators which can show the change in colour according to the strength of solution.

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  • The chemical substances which are used for identifying whether a given substance is acid or base are called ______.

    filter paper


    voltmeter


    pH meter


    indicators


  • Which indicator is used for identifying the acidic and basic characters of substances and also indicates the strength of acidic and basic characteristic of substances?

    Basic indicator
    Acidic indicator
    Ordinary indicator
    Universal indicator
  • Litmus paper is an example of ______.

    filter paper


    >ordinary indicator



    universal indicator


  • Which indicators do not give information about the strength of acidic or basic substances?

    none of these


    extra ordinary indicators


    universal indicators


    ordinary indicators


  • ______ is used for identifying the acidic and basic characters of substances.

    phenolphthalein
    ordinary indicators
    litmus
    universal indicators
  • Litmus paper is an example of ______.

    filter paper


    universal indicator


    none of the answers are correct


    ordinary indicator


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