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CHEMISTRY [5 Mark Question Answer]

Matter · ICSE STD 8 (ICSE - English Medium). 3 questions.

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[5 Mark Question Answer]

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Question 15 Marks
What do you observe when, barium chloride solution is mixed with sodium sulphate solution ?
Answer
$\underset{\text { (aq.) }}{\mathrm{BaCl}_2}+\underset{\text { (aq.) }}{\mathrm{Na}_2 \mathrm{So}_4} \longrightarrow \underset{\text { (ppt.) }}{\mathrm{BaSO}_4}+\underset{\text { (aq.) }}{2 \mathrm{NaCl}}$
We will observe that a white insoluble solid $($precipitate$)$ of barium sulphate is formed along with a solution of sodium chloride. Wait for ten minutes to complete the reaction and the solid formed to settle down.
Weigh the content again and note the reading.
We will observe that,
total mass of the apparatus $+$ reactants $=$ total mass of apparatus $+$ products
Hence the law of conservation of mass is verified.
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Question 25 Marks
What happens to water if it is heated and Explain the phenomenon of change of state of water.
Answer
Water on heating changes into steam at $100^{\circ} \mathrm{C}$
water $\xrightarrow{\text { heating }} \operatorname{steam}\left(100^{\circ} \mathrm{C}\right)$
Phenomenon of change of state of water:
Water is a liquid under ordinary conditions but, when it is kept in a deep freezer, it changes into ice at $0^{\circ} \mathrm{C}$ and when ice is kept at room temperature again changes back into liquid water.
Similarly, water on heating change into steam at $100^{\circ} \mathrm{C}$, which on cooling changes back into liquid water. But there is no change in the chemical composition of water. When its state changes from liquid to solid or liquid to gaseous state.
$\underset{\text { (solid) }}{\text { Ice }} \stackrel{\text { Heat }}{\stackrel{\text { Cool }}{\rightleftharpoons}} \underset{\text { (liquid) }}{\text { Water }} \underset{\text { Cool }}{\stackrel{\text { Heat }}{\rightleftharpoons}} \underset{\text { (gas) }}{\text { steam }}$
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Question 35 Marks
State the main postulates of kinetic theory of matter.
Answer
The main postulates of the theory are:
  1. Matter is composed of very small particles called atoms and molecules.
  2. The constituent particles of a kind of matter are identical in all respects.
  3. These particles have space or gaps between them which is known as interparticular or intermolecular space.
  4. There exists a force of attraction between the particles of matter which holds them together. This force of attraction is known as interparticular or intermolecular force of attraction.
  5. Particles of matter are always in a state of random motion and possess kinetic energy, which increases with increase in temperature and vice$-$versa.
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[5 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip