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CHEMISTRY [5 Mark Question Answer]

Water · ICSE STD 8 (ICSE - English Medium). 7 questions.

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[5 Mark Question Answer]

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7 questions · timed · auto-graded

Question 15 Marks
Match the statements in column $A$ with that in column $B$
Column $A$ Column $B$
$(a)$ deliquescent substance $(1)$ sodium bicarbonate
$(b)$ hygroscopic substance $(2)$ magnesium chloride
$(c)$ efflorestance substance $(3)$ conc. sulphuric acid
$(d)$ substance causing temporary hardness $(4)$ washing soda
Answer
Column $A$ Column $B$
$(a)$ deliquescent substance $(2)$ magnesium chloride
$(b)$ hygroscopic substance $(3)$ conc. sulphuric acid
$(c)$ efflorestance substance $(4)$ washing soda
$(d)$ substance causing temporary hardness $(1)$ sodium bicarbonate
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Question 25 Marks
Why is water very precious for all living being ?
Answer
Water is one of the most precious substances for the existence of life. Since life on the earth began in the oceans, and since no living thing can survive without water, it is rightly called the source of life.
Water forms a large part of the body mass of all living organisms $— 90\%$ of human blood is water. Water has the ability to dissolve a number of substances. Therefore, it serve as the liquid medium in which all reactions within the living body take place.
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, beans, grams, etc., contain some amount of water.
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Question 35 Marks
Define water of crystallization. Give two examples with formulae.
Answer
The fixed amount of water which is in loose chemical combination with a salt in its crystal is called water of crystallization.
Examples:
Common name Chemical name Formulae
Blue vitroil Copper sulphate pentahydrate $\ce{CuSO_4\ 5H_2O}$
Green vitriol Iron $(2)$ sulphate heptahydrate $\ce{FeSO_4\ 7H_2O}$
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Question 45 Marks
Differentiate between Suspension and colloid.
Answer
Suspension
  1. Heterogeneous
  2. Particle size greater than $10^{-7} m.$
  3. Opaque.
  4. Particles are visible.
  5. Particles of suspension settle at the bottom of the container.
  6. Particles of suspension do not pass through filter paper.
Colloid
  1. Heterogeneous.
  2. Particles size between $10^{-10}$ to $10^{-7} m.$
  3. Translucent.
  4. Particles can be seen with the help of a powerful microscope.
  5. Particles of colloids do not settle.
  6. Colloidal particles pass easily through ordinary filter paper but do not pass through ultra filters.
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Question 55 Marks
Differentiate between Solution and suspension
Answer
Solution
  1. It is an example of homogeneous mixture.
  2. Particle size less than $10^{-10}m$
  3. Transparent
  4. Solute particles can not be filtered. Solution pass easily through filter paper.
Suspension
  1. It is an example of heterogeneous mixture.
  2. Particle size greater team $10^{-7} m$
  3. Opaque
  4. Particles of suspension do not pass through filter paper.
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Question 65 Marks
What are the main causes of water pollution ? How can it be controlled ?
Answer
Main causes of water pollution are:
  • Chemical waste, industrial waste and agricultural processes.
  • Thermal waste from nuclear and thermal power plants.
  • Sewage and garbage.
Prevention of water pollution:
  • Domestic sewage should be treated before being discharged into rivers.
  • Using of non$-$biodegradable substances like detergents should be stopped.
  • Trees and plants must be planted along the banks of rivers.
  • Purification of water bodies should be carried out.
  • The waste products of industries should be treated before they are discharged into rivers.
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Question 75 Marks
Suggest one method for the removal along with the reaction for permanent hardness of water.
Answer
Removal of hardness of permanent hardness of water$-$
By Adding sodium carbonate $($washing soda$)$
Permanent hardness of water is removed when water is treated with a small quantity of sodium carbonate.
It reacts with the soluble chlorides and sulphates of calcium and magnesium to form their insoluble carbonates. These can be removed by filtration and then the water becomes soft. Sodium sulphate or sodium chloride formed after the reaction does not affect the soap.
$\underset{\text { (sodium carbonate) }}{\mathrm{Na}_2 \mathrm{CO}_3}+\underset{\text { (calcium sulphate) }}{\mathrm{CaSO}_4} \longrightarrow \underset{\text { (insoluble calcium carbonate) }}{\mathrm{Na}_2 \mathrm{SO}_4}$
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[5 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip