Page 233 - Chemistry ICSE Class IX

Chemistry Practicals 221
y Weigh a clean and dry beaker precisely. Record its mass in your notebook.
y Transfer the given mixture (~10 g)* into a beaker and weigh it precisely. Record its mass in your
notebook.
y Add distilled water (about 50 mL) and stir it to dissolve the salt present in the mixture. Allow the
beaker to stand undisturbed for some time.
y When the sand settles down, filter the solution through a filter paper set into a funnel.
y Collect all the sand on the filter paper.
y Wash the sand with a fire spray of distilled water until it is free from salt.
y Dry the sand (residue left on the filter paper) and weigh it. Record its mass in your notebook.

Observations

Mass of the beaker = m g
1
Mass of beaker + mixture = m g
2
Mass of mixture = (m g – m g) = (m – m ) g
2 1 2 1
Mass of washed and dried sand = m g
3

Calculations

Mass of sand × 100 m g × 100 m
Mass percent of sand in the mixture = = 3 = 3
Mass of the mixture (m – m )g (m – m )
2 1 2 1
m
So, Mass percent of salt in the mixture = 100 – 3 = .......................% (by mass)
(m – m )
2 1
Results

The given mixture contains .......................% (by mass) of sand and .......................% (by mass) of salt.

VIVA VOCE

1. Give two examples of heterogeneous mixtures.
Ans. (a) Salt + Sugar
(b) Iron powder + Sulphur
2. Give three examples of homogeneous mixtures.
Ans. (a) Solution of sugar in water
(b) Solution of common salt in water
(c) Kerosene
3. Is air a mixture or a chemical compound? Is it homogeneous or heterogeneous?
Ans. Air is a mixture. Commonly air contains dust, smoke particles and other suspended impurities. So, air is a heterogeneous
mixture. However, pure and clean air is a homogeneous mixture of gases, mainly nitrogen, oxygen, carbon dioxide and
argon.
4. Which of these has a fixed composition — a mixture or compound?
Ans. A compound has a fixed composition.

Note for the laboratory instructor
The solubility of salt at 20°C is 37 g per 100 g of water. Therefore, the mixture should contain such a quantity of salt that it dissolves in the water
added. As a typical case, 10 g of mixture may be prepared by using 6 g salt and 4 g sand.