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Question

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Give the properties of plaster of Paris.

Solution

On heating gypsum at 373K, it loses water molecule and becomes calcium sulphate hemihydrate(CaSO₄.1/2H₂O).

Properties of plaster of Paris:
(i) It is a white powder.
(ii) Setting property: When wetted with water, this forms a solid plastic mass and heat is given out during this process and finally a hard porous mass results within 10-15 minutes. This involves two steps. Firstly, water is absorbed to form orthorhombic dihydrate and change to monoclinic, when the plaster hardens, thus setting takes place.

${CaSO}_{4} . \frac{1}{2} H_{2} O \to_{setting}^{H_{2} O} {CaSO}_{4} . 2 H_{2} O \underset{Hardening}{\to} {CaSO}_{4} . 2 H_{2} O Orthohombic Monoclinic dihydrate dihydrate$

Some More Questions From Control and Coordination Chapter

Give two physical characteristics each of acids and bases.

What are indicators? Name four acid-base indicators and mention their colour change.

What are antacids?

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.

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