25
Section
a) A beam of light is passed through three samples of mixtures and the
observations are noted down as follows:
Solution A - scatters beam of light excessively
IL Solution 3-path of light is not visible
III. Solution C-path of light is visible as a beam of light
Identify samples A, B and C and write another characteristic property
each sample
Answers
Types of Mixtures
Depending upon the nature of the components that form a mixture, we can have different types of mixtures.
Activity : 1
Let us divide the class into groups A, B, C and D.
• Group A takes a beaker containing 50 mL of water and one spatula full of copper sulphate powder.
• Group B takes 50 mL of water and two spatula full of copper sulphate powder in a beaker.
• Groups C and D can take different amounts of copper sulphate and potassium permanganate or common salt (sodiumchloride) and mix the given components to form a mixture.
• Report the observations on the uniformity in colour and texture.
Observations:
• Groups A and B have obtained a mixture which has a uniform composition throughout. Such mixtures are called homogeneous mixtures or solutions. Some other examples of such mixtures are: (i) salt in water and (ii) sugar in water. Compare the colour of the solutions of the two groups. Though both the groups have obtained copper sulphate solution , 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 sodium chloride and iron filings, salt and sulphur, and oil and water are examples of heterogeneous mixtures.
Activity: 2
Let us again divide the class into four groups – A, B, C and D.
Distribute the following samples to each group:
Few crystals of copper sulphate to group A.
One spatula full of copper sulphate to group B.
Chalk powder or wheat flour to group C.
Few drops of milk or ink to group D.
Each group should add the given sample in water and stir properly using a glass rod. Are the particles in the mixture visible?
Direct a beam of light from a torch through the beaker containing the mixture and observe from the front. Was the path of the beam of light visible?
Leave the mixtures undisturbed for a few minutes (and set up the filtration apparatus in the meantime). Is the mixture stable or do the particles begin to settle after some time? Filter the mixture. Is there any residue on the filter paper?
Inference:
Groups A and B have got a solution.
Group C has got a suspension.
Group D has got a colloidal solution.
Explanation:
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