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Control and Coordination
Indicators are chemical substances which give different colours in acidic or basic solutions.
(i) Methyl orange gives pink colour with acid solution and yellow colour with base solution.
(ii) Phenolphthalein is colourless in acid solution while it turns into pink colour in base solution.
(iii) Litmus solution turns red in acid solution and blue in base solution.
(iv) Bromothymol blue is blue in base solution and is yellow in acid solution.
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You are given the following solutions:
Hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), sodium hydroxide (NaOH), calcium hydroxide [(Ca(OH)2], potassium hydroxide (KOH), magnesium hydroxide [Mg(OH)2] and ammonium hydroxide (NH4OH). Give the colour change for each of these solutions with red litmus, blue litmus, phenolphthalein and methyl orange solutions.
Choose the olfactory indicators and give their characteristics: red cabbage extract, onion, vanilla extract, litmus, clove oil.
Take 5 ml hydrochloric acid in a boiling tube or a conical flask. Add a few pieces of zinc granules to it.
(a) What do you observe on the surface of zinc granules?
(b) Name the gas evolved.
(c) What happens when the above gas is passed through soap solution?
(d) What happens when a burning candle is brought near the gas filled tube?
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