Note on Indicators

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An indicator is a substance which changes color in the presence of acids or alkalis. In the laboratory, we use three indicators. These are litmus, phenolphthalein, and methyl orange.

Indicator Acid Base
Red litmus No change in color Blue in color
Blue litmus Red in color No change in color
Phenolphthalein Colorless Rose color
Methyl orange Red in color Yellow in color

Turmeric powder mixed with water is a bright orange-yellow which turns a brick red in the presence of alkali. Indicator can be prepared by boiling, mashing and straining a finely chopped beetroot. Many red or blue colored flowers contain natural dyes which can be used as indicators.

pH Scale

The pH scale is a standard scale, which is used for measuring the approximate strength of an acid or an alkali solution.

The pH scale has ranged from 1 to 14. Acidic solutions have a pH value less than 7 while alkaline solutions have a pH value greater than 7. Distilled water has pH value 7 and is called neutral substance. Strong acids have pH value 1 or 2 while strong alkali's have pH value 13 or 14.

From the pH scale, we can say that higher the hydrogen ion concentration, lower is the pH value and vice versa.

  • An indicator is a substance which changes color in the presence of acids or alkalis.
  • In the laboratory, we use three indicators. These are litmus, phenolphthalein and methyl orange.
  • Many red or blue colored flowers contain natural dyes which can be used as indicators.
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Very Short Questions

An indicator is a chemical substance which has capacity to show the termination of a chemical reaction by changing its colour.

The types of indicators are: litmus paper, phenolphthalein, methyl orange and turmeric.

An indicator is used to test whether a substance is acid or base.

Blue litmus turns into red in an acidic medium.

Red litmus turns to blue in basic medium.

The pH scale is a standard scale, which is used for measuring the approximate strength of an acid or an alkali solution. The pH scale has ranged from 1 to 14.

Turmeric powder mixed with water is a bright orange-yellow which turns a brick red in the presence of alkali.

The pH scale is a standard scale, which is used for measuring the approximate strength of an acid or an alkali solution.The pH scale has ranged from 1 to 14. Acidic solutions have a pH value less than 7while alkaline solutions have a pH value greater than 7. Distilled water has pH value 7 and is called neutral substance. Strong acids have pH value 1 or 2 while strong alkali's have pH value 13 or 14.

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  • Which of these is not a natural indicator?

    china rose


    methyl orange


    turmeric solution


    litmus


  • Blue litmus when gets in contact with acid changes to ______.

    red


    pink


    no change in color


    orange


  • Red litmus when gets in contact with acid changes to ______.

    dark red colour.
    There is no change in color.
    pink colour.
    blue colour.
  • Blue litmus when gets in contact with base changes to ______.

    nothing. There is no change in color.


    pink


    orange


    dark red


  • Red litmus when gets in contact with base changes to ______.

    pink


    blue


    orange


    nothing. There is no change in color.


  • Which one of these is an olfactory indicator?

    turmeric solution
    blue litmus
    Onion
    red litmus
  • Methyl orange when comes in contact with acid changes to ______.

    orange


    remain colorless


    blue


    red


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Dixu

How is indicators different from the ordinary indicator?


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Mina

give the name of more indicators.


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