Why is Plaster of Paris written as CaSO 4 . 1 2 H 2 O ? How is it possible to have half a water molecule attached to CaSO 4 ?

Plaster of Paris is prepared by heating gypsum at 373 K . The balanced equation is as follows: CaSO 4 . 2 H 2 O Gypsum → 373 k CaSO 4 . 1 2 H 2 O Plaster of paris + 3 2 H 2 O Water . It is not possible to have half a molecule of water. Therefore, actual formula must be 2 CaSO 4 . H 2 O . This means that, two molecules of calcium sulphate shares one molecule of water. Thus, the effective number of water molecules for one calcium sulphate is half. However, for the sake of simplicity, the plaster of Paris is shown as CaSO 4 . 1 2 H 2 O . That is, only half water molecule is shown as the water of crystallisation.

E M B I B E

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 23

MEDIUM

10th CBSE

IMPORTANT

Earn 100

What are olfactory indicators? Explain.

Important Questions on Acids, Bases and Salts

MEDIUM

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 24

Dry

HCl

gas does not change the colour of dry blue litmus paper, why?

MEDIUM

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 24

Antacid tablets are used by a person suffering from stomach pain, why?

HARD

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 25

Why is Plaster of Paris written as

{CaSO}_{4} . \frac{1}{2} H_{2} O

? How is it possible to have half a water molecule attached to

{CaSO}_{4}

?

MEDIUM

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 25

Why is sodium hydrogen carbonate an essential ingredient in antacids?

MEDIUM

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 26

Why does bee sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How?

HARD

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 27

A substance

X

used as an antacid reacts with hydrochloric acid to produce a gas

Y

which is used in fire extinguishers.
(a) Name the substances

X

and

Y

.
(b) Write a balanced equation of the reaction between X and hydrochloric acid.

MEDIUM

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 28

The blue colour of crystals of a substance changed to white on heating in a closed test tube but the colour was regained after sometime on cooling. Name the substance and write its chemical formula. Explain the phenomenon involved.

MEDIUM

10th CBSE

IMPORTANT

SUPER SIMPLIFIED SCIENCE CHEMISTRY CLASS X>Chapter 2 - Acids, Bases and Salts>Test Your Knowledge>Q 29

While diluting a mineral acid why is it recommended to add acid slowly to water and not water to acid. Explain.