4.1 describe the use of the indicators litmus, phenolphthalein and methyl orange to distinguish between acidic and alkaline solutions

The dye in these indicator changes colour depending on whether the substance you are testing is alkaline or acidic (above or below pH7).

Litmus - red in acidic solutions (under pH7), blue in alkaline solutions(above pH7), purple in neutral solutions (pH7)

Phenolphthalein - colourless in acidic solutions (under pH7), bright pink in alkaline solution (above pH7)

Methyl orange - red in acidic solutions (under pH7), yellow in alkaline solutions (above pH7)