Consider the following statements:
(a) Both acids and bases change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator.
Which of these statements are correct?
(i) All four
(ii) (a) and (d)
(iii) (b) and (c)
(iv) only (d)
Correct answer: (ii) (a) and (d)
Explanation: Both acids and bases change colour of all indicators and the change of colour in an acid and a base depends on the type of the indicator. Hence, both statements are true.
The different colours showed by some indicators are given below:
| Acids | Bases |
a. Acids remains colourless in phenolphthalein indicator b. Acids turn blue litmus to red. c. Acids do not change the colour of turmeric (yellow). d. Acids give a pH of 1-7. | a. Bases gives pink colour in phenolphthalein indicator. b. Bases turn red litmus to blue. c. Bases turn turmeric from yellow to red. d. Bases give a pH of 7-14.
|
[Extra information: Indicators are substances that show acidic or basic behaviour of other substances by showing a change in colour. There are different types of indicators. These are :
Natural indicators like turmeric and litmus.
Synthetic indicators like Methyl orange and phenolphthalein.
Olfactory indicators like onion and vanilla extract.
Universal indicators like pH.]
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