If a base is slowly added to an acidic solution, in which direction can the colour of universal indicator change?
Answer and explanation
Correct answer: From more acidic colours towards neutral colour
The governing concept is neutralisation and the corresponding movement of pH. An acidic solution initially has a pH below 7. As a base is added gradually, hydroxide ions react with hydrogen ions to form water, so acidity decreases and the pH moves toward 7. The universal-indicator colour can therefore shift from acidic colours, such as red or orange, toward green or another neutral colour. It may later become basic if excess base is added, but A correctly describes the initial direction.
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What is the correct answer to this question?
From more acidic colours towards neutral colour
Why is this the correct answer?
The governing concept is neutralisation and the corresponding movement of pH. An acidic solution initially has a pH below 7. As a base is added gradually, hydroxide ions react with hydrogen ions to form water, so acidity decreases and the pH moves toward 7. The universal-indicator colour can therefore shift from acidic colours, such as red or orange, toward green or another neutral colour. It may later become basic if excess base is added, but A correctly describes the initial direction.
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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