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CHEMISTRY [5 Mark Question Answer]

Matter · ICSE STD 8 (ICSE - English Medium). 4 questions.

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[5 Mark Question Answer]

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4 questions · timed · auto-graded

Question 14 Marks
State the ‘law of conservation of mass’. State the main points of Landolt’s experiment for experimental evidence of the law.
Answer
Law of Conservation of Mass :
"In any chemical reaction, the total mass of the reacting substances is equal to the total mass of the products of the reaction provided masses are measured under similar conditions."
Landolt's experiment :
To illustrate the law of conservation of mass. Two solutions $- \ce{NaCl}$ in limb $A$ and $\ce{AgNO_3}$ sol. in limb $B$ were taken in $U-$shaped tube and weighed
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Now tube was tilted so that two solutions get mixed and react with each other to form new products. Tube is weighed again Weight after reaction was found to be same as before reaction.
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Total mass of reactants $=$ Total mass of products This verifies the law.
Two other examples are :
$(i)$ We can take two solutions of lead acetate $\ce{Pb \left(CH_3OO\right)_2}$ in limb $A$ and sodium sulphate $\ce{Na_2SO_4}$ in limb $B$ in the $U$-shaped tube.
$\ce{Pb \left(CH_3COO\right)_2 + Na_2SO_4 \rightarrow PbSO _4+2 CH _3 COONa}$
$(ii)$ We can also take two solutions of iron $\ce{[II]}$ sulphate $\ce{FeSO_4}$ in limb $A$ and silver sulphate $\ce{Ag_2SO_4}$; in limb $B$ in $U-$shaped tube still the result is found to be same.
$\ce{2FeSO_4 + Ag_2 SO_4 \rightarrow 2 Ag \downarrow+ Fe_2\left(SO_4\right)_3}$
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Question 24 Marks
With reference to inter-conversion of matter $–$ on the basis of kinetic theory $–$ explain in brief the conversion of:
$(a)$ A solid into a liquid
$(b)$ A liquid into vapour $[$or gas$]$
$(c)$ Vapour [or gas] into a liquid
$(d)$ A liquid into a solid
With special reference to inter$-$particle space $\&$ interparticle attraction at the different stages of conversion.
Answer
$(a)$ A solid into a liquid : Kinetic energy increases
  • Heat energy is absorbed by the molecules and stored in the form of potential energy.
  • Inter$-$particle space-increases.
  • Inter$-$particle attraction-decreases.
  • Collision$-$increases and push apart.
  • Solid changes into liquid.
$(b)$ A liquid into vapour $[$or gas$]$ :
  • Heat energy absorbed $-$stored as potential energy.
  • Inter-particle space$-$increases.
  • Inter-particle attraction$-$decreases $($almost negligible$)$.
  • Collision$-$increase and particles push apart become free and escape gas.
  • Liquid changes into vapours.
$(c)$ Vapour $[$or gas$]$ into a liquid :
  • Potential energy released in the form of heat energy.
  • Inter$-$particle space$-$decreases considerably.
  • Inter$-$particle attraction-increases.
  • Collision$-$decrease to negligible particles are not in a position to be free.
  • Vapours changes into liquid state.
$(d)$ A liquid into a solid :
  • Potential energy $($stored$)$ is$-$released.
  • Inter$-$particle space-decreases.
  • Inter$-$particle attraction-increases. Particles are not in position to be free.
  • Collision$-$decreases.
  • Liquid changes into solid.
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Question 34 Marks
Draw a labelled schematic diagram representing the terms $(a)$ to $(e)$ involved in the inter-conversion of matter.
Answer
$(a)$ Melting $–$
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$(b)$ Vaporisation $–$
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$(c)$ Liquefaction or condensation $–$​​​​​​​
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$(d)$ Solidification or Freezing $–$​​​​​​​
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$(e)$ Sublimation $–$​​​​​​​
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Question 44 Marks
State which of the three states of matter Le. solids, liquids or gases $–$ have
$(a)$ No definite volume
$(b)$ A definite shape
$(c)$ High density
$(d)$ No free surfaces
$(e)$ Particles $–$ which diffuse very easily.
Answer
$(a)$ Gases
$(b)$ Solids
$(c)$ Solids
$(d)$ Gases
$(e)$ Gases
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[5 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip