If damp red litmus paper turns blue, which gas is present?

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Study for the IGCSE Edexcel Chemistry Test. Access flashcards and multiple choice questions with hints and explanations. Get ready for your exam!

Multiple Choice

If damp red litmus paper turns blue, which gas is present?

Explanation:
Red litmus paper turns blue in basic conditions. Ammonia gas dissolves in water to form hydroxide ions (NH3 + H2O ⇌ NH4+ + OH−), making the solution alkaline and turning the damp red litmus blue. Oxygen and hydrogen are neutral and don’t make the paper blue, while chlorine would produce acidity in water, turning the red litmus back toward red. So the gas present is ammonia.

Red litmus paper turns blue in basic conditions. Ammonia gas dissolves in water to form hydroxide ions (NH3 + H2O ⇌ NH4+ + OH−), making the solution alkaline and turning the damp red litmus blue. Oxygen and hydrogen are neutral and don’t make the paper blue, while chlorine would produce acidity in water, turning the red litmus back toward red. So the gas present is ammonia.

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