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Chemistry : Indicators, pH & Litmus

apid Theory you need to know!

Indicators are chemical substances that are used to find out whether a given solution is acidic or alkaline by showing a color change.

pH Indicator

The pH indicator indicates the nature as well as the strength of the given medium (solution).

Examples of pH Scale Readings

A pH scale reading of less than 7 indicates an acidic medium.

A pH scale reading of more than 7 indicates a basic medium.

A pH scale reading equal to 7 indicates a neutral medium or solution (pure distilled water).

A pH scale reading of 2 indicates a strong acid.

A pH scale reading of 13 indicates a strong base.

A pH scale reading of 6 indicates a weak acid.

A pH scale reading of 8 indicates a weak base.

Litmus Indicator

Acids turn blue litmus paper red.

Bases turn red litmus paper blue.

Examples of Litmus Paper Color Changes

Sulfuric acid is obviously acidic in nature. It turns blue litmus paper red.

Sodium hydroxide is a base. It turns red litmus paper blue.

Other Indicators

Phenolphthalein solution is a colorless indicator.

Methyl orange solution is obviously an orange-colored indicator.

Bromothymol blue solution is an indicator.

Examples of Color Changes using Other Indicators

Phenolphthalein solution causes no color change in acids whereas it turns bases pink.

Methyl orange solution turns acids pink whereas it turns bases yellow.

Bromothymol blue solution turns acids yellow whereas it turns bases blue.



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