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

Litmus (reliable)

o   ACIDS: turns red
o   NEUTRAL: purple

o   ALKALIS: blue

·      Comes in:

o   RED litmus paper

§  ACIDS: stays red
§  NEUTRAL: stays red

§  ALKALIS: turns blue

o   BLUE litmus paper

§  ACIDS: turns red
§  NEUTRAL: stays blue

§  ALKALIS: stays blue

·      
PPhenolphthalein

o   ACIDS: colourless

o   ALKALIS: pink

§  Is insoluble in water

§  Colour changes sharply around ph of 8

·      Methyl orange

o   STRONG ACIDS: Red (3)

o   WEAK ACIDS: Orange/yellow (4-14)

o   ALKALIS: Yellow

o   NEUTRAL: Yellow

§  Is yellow in both neutral and base solutions as they fall after its colour change