Page 47 - Understanding NCERT Science 09

Exercises

1. A 0.24 g sample of compound of oxygen and boron was found
by analysis to contain 0.096 g of boron and 0.144 g of oxygen.
Calculate the percentage composition of the compound by
weight.
2. When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of
carbon dioxide is produced. What mass of carbon dioxide will
be formed when 3.00 g of carbon is burnt in 50.00 g of
oxygen? Which law of chemical combination will govern your
answer?
3. What are polyatomic ions? Give examples.
4. Write the chemical formulae of the following.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.
5. Give the names of the elements present in the following
compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
6. Calculate the molar mass of the following substances.
(a) Ethyne, C H
2 2
(b) Sulphur molecule, S
8
(c) Phosphorus molecule, P (Atomic mass of phosphorus
4
= 31)
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO
3

Group Activity

Play a game for writing formulae.
Example1 : Make placards with symbols and valencies of the
elements separately. Each student should hold two
placards, one with the symbol in the right hand and
the other with the valency in the left hand. Keeping
the symbols in place, students should criss-cross their
valencies to form the formula of a compound.

36 SCIENCE

Rationalised 2023-24