Page 26 - Understanding NCERT Science 09
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colour of the solutions of the two
groups. Though both the groups have
obtained copper sulphate solution but
the intensity of colour of the solutions
is different. This shows that a
homogeneous mixture can have a
variable composition.
• Groups C and D have obtained
mixtures, which contain physically
distinct parts and have non-uniform
compositions. Such mixtures are called
heterogeneous mixtures. Mixtures of Fig. 2.2: Filtration
sodium chloride and iron filings, salt Now, we shall learn about solutions,
and sulphur, and oil and water are suspensions and colloidal solutions in the
examples of heterogeneous mixtures.
following sections.
Activity ______________ 2.2 uestions
• Let us again divide the class into four 1. What is meant by a substance?
groups— A, B, C and D. Q 2. List the points of differences
• Distribute the following samples to between homogeneous and
each group: heterogeneous mixtures.
− Few crystals of copper sulphate
to group A.
− One spatula full of copper
sulphate to group B. 2.2 What is a Solution?
− Chalk powder or wheat flour to
group C. A solution is a homogeneous mixture of two
− Few drops of milk or ink to or more substances. You come across various
group D. types of solutions in your daily life. Lemonade,
• Each group should add the given soda water, etc., are all examples of solutions.
sample in water and stir properly Usually we think of a solution as a liquid that
using a glass rod. Are the particles contains either a solid, liquid or a gas dissolved
in the mixture visible? in it. But, we can also have solid solutions
• Direct a beam of light from a torch (alloys) and gaseous solutions (air). In a
through the beaker containing the solution there is homogeneity at the particle
mixture and observe from the front. Was level. For example, lemonade tastes the same
the path of the beam of light visible? throughout. This shows that particles of sugar
• Leave the mixtures undisturbed for or salt are evenly distributed in
a few minutes (and set up the the solution.
filtration apparatus in the meantime).
Is the mixture stable or do the
Alloys: Alloys are mixtures of two or
particles begin to settle after some
time? more metals or a metal and a non-metal
• Filter the mixture. Is there any and cannot be separated into their
residue on the filter paper? components by physical methods. But
still, an alloy is considered as a mixture
• Discuss the results and form an More to know because it shows the properties of its
opinion. constituents and can have variable
Groups A and B have got a solution. composition. For example, brass is a
Group C has got a suspension. mixture of approximately 30% zinc and
Group D has got a colloidal solution. 70% copper.
IS MATTER AROUND US PURE? 15
Rationalised 2023-24
