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Control And Coordination

Question

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${CaSO}_{4} . \frac{1}{2} H_{2} O$ is used as plaster of Paris but CaSO₄ is used as a drying agent and cannot replace plaster of Paris. Explain.

Solution

Anhydrous calcium sulphate (CaSO₄) takes up water readily and forms hydrated salt and so is used as a drying agent,

CaSO₄ + 2H₂O → CaSO₄ · 2H₂O

${CaSO}_{4} . \frac{1}{2} H_{2} O$ has a particular crystal structure which imparts property of setting and hardening on mixing with water. CaSO₄ cannot replace plaster of paris because on mixing with water it does not acquire the property of setting and hardening.

Some More Questions From Control and Coordination Chapter

What are olfactory indicators?

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.

What do you understand by concentrated and dilute acids?

How do metals react with bases?

What is a neutralization reaction? Give some examples.

What are non-metallic oxides? Substantiate your answer.

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?

Name four acids and bases. Write their formulae.

Name the various kind of oxides and mention their properties.

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