Answer the following questions briefly.
1. Distinguish between homogeneous and heterogeneous mixtures.
2. Mention the appropriate methods for the separation of the following mixtures:
(a) A mixture in which the components have different weights.
(b) A mixture that has components of different sizes.
3. Mary was asked to use sedimentation process to clean rice that her mother had
brought from the mill before cooking. Why?
What is filtration?
Why does the quantity of various substances dissolving in water vary? Give an example.
6. How can the solubility of a solute be increased?
Answers
Answer:
Question 1:
Most of the substances we see around us are
(a) pure elements.
(b) pure compounds.
(c) impure elements.
(d) mixtures.
ANSWER:
(d) mixtures
Most of the substances we see around us are mixtures of different elements and compounds.
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Question 2:
A solution of salt in water is a
(a) compound.
(b) homogeneous mixture.
(c) heterogeneous mixture.
(d) element.
ANSWER:
(b) homogeneous mixture
When salt is dissolved in water, the salt is distributed uniformly in the solution. Thus, the salt solution is a homogeneous mixture.
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Question 3:
The property used in separating a mixture of two solids by winnowing is
(a) difference in colour.
(b) difference in size.
(c) difference in weight.
(d) attraction by magnet.
ANSWER:
(c) difference in weight
Winnowing is used to separate two solids of different weights, such as wheat and chaff.
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Question 4:
The process of settling down of particles of a solid in a liquid is
(a) decantation.
(b) sublimation.
(c) sedimentation.
(d) filtration.
ANSWER:
(c) sedimentation
The process of settling down of particles of a solid in a liquid is known as sedimentation.
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Question 5:
Which method is used to obtain a pure liquid from a solution?
(a) distillation
(b) condensation
(c) filtration
(d) loading
ANSWER:
(a) distillation
Distillation can be used to obtain a pure liquid from a solution.
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Question 6:
The temperature of a saturated solution of sugar in water is raised by 10 °C. Which of these statements is now true?
(a) It will continue to be saturated.
(b) It will become unsaturated.
(c) Whether it remains saturated or becomes unsaturated depends on the amount of water taken.
(d) It will continue to be saturated, but if the temperature is increased beyond 10 °C it will become unsaturated.
ANSWER:
(b) it will become unsaturated
If the temperature of saturated sugar solution is increased by 10 oC, then more sugar can be dissolved in the solution and the solution becomes unsaturated.
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Question 7:
Which of the following can dissolve in water?
(a) only solids
(b) only solids and liquids
(c) solids, liquids and gases
(d) only liquids
ANSWER:
(c) solids, liquids and gases
Solids such as salt, liquids such as alcohol and gases such as nitrogen and oxygen can dissolve in water.
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Question 8:
Sedimentation and decantation are useful to separate
(a) immiscible liquids.
(b) soluble solid from liquid.
(c) insoluble solid from liquid.
(d) insoluble solid from a liquid where the solid is heavier than the liquid.
ANSWER:
(d) insoluble solid from a liquid where the solid is heavier than the liquid
Decantation and sedimentation can be used to separate solids from a liquid when the solid is heavier than the liquid and is insoluble in the liquid.
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Question 9:
A commonly used chemical for loading is
(a) hydrogen.
(b) alum.
(c) sulphur.
(d) common salt.
ANSWER:
(b) alum
Alum is a commonly used chemical for loading to speed up sedimentation.
Explanation:
hope it works.........