Universal indicator is red in a solution. After adding water, the colour becomes orange. What does this show?
Answer and explanation
Correct answer: Acidity decreased but the solution is still acidic
The governing concept is dilution of an acid and the colour scale of a universal indicator. Red indicates a strongly acidic solution. Adding water increases the volume, so the concentration of hydrogen ions per unit volume decreases and the acidity becomes weaker. However, dilution does not automatically remove all hydrogen ions or create a base. The orange colour therefore indicates that the solution is still acidic, but less acidic than before. Hence option A is correct; B, C, and D contradict the indicator change.
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What is the correct answer to this question?
Acidity decreased but the solution is still acidic
Why is this the correct answer?
The governing concept is dilution of an acid and the colour scale of a universal indicator. Red indicates a strongly acidic solution. Adding water increases the volume, so the concentration of hydrogen ions per unit volume decreases and the acidity becomes weaker. However, dilution does not automatically remove all hydrogen ions or create a base. The orange colour therefore indicates that the solution is still acidic, but less acidic than before. Hence option A is correct; B, C, and D contradict the indicator change.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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