Question

What are the limitations of litmus paper and phenolphthalein indicators? Name two other indicators that can be used that do not have such limitations.

Answer 1

Explanation:

It can only detect the difference between strongly acidic and basic solutions. Litmus paper turns red below pH < 4.5 and turns blue at pH > 8.3. It cannot test changes in pH between this range which is where neutral pH is located (pH 7).

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Answer 2

Answer:

What is litmus paper and phenolphthalein?

Litmus paper and phenolphthalein are the indicators to indicate the acidity and basicity of a chemical.

Litmus paper

• Blue litmus paper turns red in acidic conditions.
• Red litmus paper turns blue in basic conditions.

Phenolphthalein

• It is pink in colour.
• It turns colourless in an acidic medium.
• It turns purple in basic medium.

Limitations of litmus paper and phenolphthalein:

• They do not give the numerical pH value.
• Can differentiate only between a very strong acid and base.
• The colour change can be for reasons other than acid- base reactions.

Two other indicators are:

1. Universal indicator
2. Methyl orange

             These indicators give a characteristic colour corresponding to different pH value therefore, numerical value can be determined.