Class-8 Dalal New Simplified ICSE Chemistry Matter

Exercise-1

Question 1.

Explain the meaning of the term ‘matter’.
Answer 1
Anything that has mass, occupies space and can be felt by the sense organs are called matter.

Question 2.
Matter in any state is composed of small particles – molecules, atoms or ions. Differentiate the terms above in Italics.
Answer 2
Molecules : the smallest particle of a substance that can exist separately , e.g. N₂, Br₂, Cl₂ are molecules.
Atoms : the smallest particle of an element which can take part in all chemical reaction and is the basic unit of matter, e.g. Fe, Au, Hg are example of atoms.
Ions : atom or a group of atoms which has a charge due to loss or gain of electrons, e.g. Ca^2-, Na¹⁺, Cl^1-– are ions.

Question 3.
Differentiate between the-two characteristics of matter – ‘mass’ & ‘weight’.
Answer 3
Mass :

1. amount of matter in a body and never change place to place
2. It is measured in Kilograms (kg) by beam balance

Weight :

1. It is the force of attraction that pull of gravity on a body.
2. It is measured in Newtons (N)and change value place to place

Question 4.
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 4.

(a) Gases
(b) Solids
(c) Solids
(d) Gases
(e) Gases

Question 5.
State the main postulates of the kinetic theory with special reference to –

(a) Inter-particle space
(b) Inter-particle attraction
(c) Energy possessed by particles of matter.

Answer 5.

(a) Inter-particle space : The particles of matter are arranged in a way such that they have spaces existing between them. i.e. inter molecular space.
(b) Inter-particle attraction : particles of matter attract each other with a force of attraction which is inversely proportional to distance

(c) Energy possessed by particles of matter : particles are in continuous motion, and has mass so they, possess energy called kinetic energy.

Question 6.
State in which of the following examples ie. a piece of wood, water, a light gas is the

(a) Inter-particle space maximum
(b) Inter-particle attraction maximum
(c) Energy possessed by particles of matter, very large.

Answer 6

(a) A light gas
(b) a piece of wood
(c) a light gas

Question 7.
In which of the three states of matter – solids, liquids or gases is the movement of atoms about their own position. Give a reason for the same.
Answer 7

Solid

Reason– because of Minimum Inter Particle space and very strong inter – particle attraction among atoms.

Question 8.
‘Inter-particle attraction between atoms of gases is very weak’. State five properties of gases which correlate as a consequence of the weak inter-particle attraction between particles of gases.
Answer 8
The five properties of gases which correlate as a consequence of the weak inter-particle attraction between particles of gases are :

• Gases have no definite volume.
• It have no definite shape.
• They have enough space between molecules
• they are compressible
• they have low density
• the diffuse faster

Question 9.

What is inter-conversion of matter. Give the meaning of the terms involved in inter-conversion of matter

(a) Melting
(b) Vaporisation
(c) Liquefaction or condensation,
(d) Solidification or freezing
(e) Sublimation.

Answer 9
Interconversion of matter :
“Change of state of matter from one state to another state and back to its original state is called inter-conversion of matter.”

(a) Melting–Conversion of a solid into a liquid on heating ex–. ice to water.

(b) Vaporisation–Conversion of a liquid into vapours (or gas) on heating ex–. water to water vapour.

(c) Liquefaction or condensation– Conversion of vapor (or gas) into a liquid on cooling ex-. water vapour to water.

(d) Solidification or freezing– Conversion of a liquid into a solid ex-. water to ice.

(e) Sublimation.–Conversion of a solid directly into gas state ex-. Naphthalene sublimes at room temperature.

Question 10.

Draw a labelled schematic diagram representing the terms (a) to (e) involved in the inter-conversion of matter.
Answer 10
(a) Melting

(b) Vaporisation

(c) Liquefaction or condensation

(d) Solidification or freezing

(e) Sublimation

 

Question 11.
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 & inter particle attraction at the different stages of conversion.
Answer 11
(a) when A solid convert into a liquid :

• Inter-particle space-increases.
• Force of attraction -decreases.
• Collision-increases .
• Kinetic energy increases
• Heat energy is absorbed by the molecules and stored in the form of potential energy.

(b) When A liquid change into vapour

1. Kinetic energy increase.
2. Inter-particle space-increases.
3. Force of attraction-decreases
4. Collision-increase

(c) When a Vapour change into a liquid :

 

1. Kinetic energy decrease
2. Inter-particle space-decreases considerably.
3. Force of attraction -increases.
4. Collision-decrease

(d) When A liquid change into a solid :

1. Kinetic energy decrease.
2. Inter-particle space-decreases.
3. Force of attraction-increases. Particles are not in position to be free.
4. Collision-decreases.

Question 12.

On the basis of kinetic theory explain why, ammonium chloride sublimes and goes from solid state directly into vapour state.
Answer 12
Ammonium Chloride sublimes and It convert from solid state directly into vapour state because if low inter-particle attraction.
Question 13.

State the ‘law of conservation of mass’. State the main points of Landolt’s experiment for experimental evidence of the law.
Answer 13
Law of Conservation of Mass : “Mass can not be created nor destroyed during reaction.”

Landolt’s experiment : To explain the law of conservation of mass. Two solutions – NaCl in limb A and AgNO₃ sol. in limb B were taken in U-shaped tube and weighed.

Now tube was tilted so that two solutions get mixed and react with each other to form new products. Tube is weighed again after cold

Conclusion-
Weight after reaction was found to be same as before reaction.

Hence confirming the Law of Conservation of Mass

OBJECTIVE TYPE QUESTIONS

Matter Class-8 Dalal New Simplified ICSE Chemistry Middle School Allied Publishers Solutions

Q.1. Select the correct answer from A, B, C, D & E for each statement given below:
A: Solid
B: Vaporization
C: Ion
D: Gases
E: Heat

Question 1.
An atom or group of atoms – having a resultant charge.
Answer 1
C : Ion

Question 2.
The state of matter which has – least density & no free surfaces.
Answer 2
D : Gases

Question 3.
In Landolt’s experiment – the form in which the chemical energy stored up in the reactants – is released.
Answer 3
E : Heat

Question 4.
The process of change of a liquid into vapour, [gas] on heating.
Answer 4
B : Vaporization

Question 5.
The state of matter, where the inter-particle attraction between particles is maximum.
Answer 5
A : Solid

 

Q.2. With reference to the liquid state of matter – answer the following

Question 1.

On heating the liquid, do the particles gain or lose energy.
Answer 1
Gain energy.

Question 2.
The heat energy supplied to the liquid is absorbed by its molecule & stored as which form of energy.
Answer 2
Potential energy.

Question 3.
How does the stored energy, have effect on inter-particles space.
Answer 3
Stored potential energy increases the space.

Question 4.
State why the inter-particles attraction decreases to negligible.
Answer 4
because distance between particles increases, hence force of attraction decreases resulting to Inter-particle attraction to almost negligible.

Question 5.
At what point will the particles become free and escape as gas.
Answer 5
on boiling point particles become free and escape as gas

 

Q.3. Complete the statement by filling the blanks with the correct word from the brackets.

Question 1.
In naphthalene, the inter-particle attraction is __ [high/low].
Answer 1
In naphthalene, the inter-particle attraction is low.

Question 2.
The law of conservation of mass, is strictly valid if mass and __ [energy/volume] are considered together.
Answer 2
The law of conservation of mass, is strictly valid if mass and energy are considered together.

Question 3.
When inter-particle space increases, the inter-particle attractive force __ [decreases/increases].
Answer 3
When inter-particle space increases, the inter-particle attractive force decreases.

Question 4.
Kinetic energy of molecules in helium is __ [large / very large] compared to the kinetic energy of molecules in water.
Answer 4
Kinetic energy of molecules in helium is large compared to the kinetic energy of molecules in water.

Question 5.
Conversion of vapour [or gas] into a liquid is termed __ [liquefaction/vaporization].
Answer 5
Conversion of vapour [or gas] into a liquid is termed liquefaction.

Q.4. Give reasons for the following

Question 1.

Particles of matter possess energy called kinetic energy.
Answer 1
Due to continuous motion of particle moving, hence they possesses kinetic energy.

Question 2.
Solids cannot be compressed, but gases are highly compressible.
Answer 2

Solid has least space among them while gas has most space hence Solids cannot be compressed, but gases are highly compressible.

Question 3.
Kinetic energy of molecules of gases is very large & of solids, the least.
Answer 3
The Kinetic Energy of molecules of gases is very large because its particle moves fastest due to least force of attraction

Question 4.

On heating a sublimable solid, the molecules break free & escape from surface of the solid directly into vapour.
Answer 4
heating a sublimable solid the inter-particle attraction is overcome and the molecules break-free and escapes from the surface of the solid directly into the vapour.

Question 5.
Particles of matter move more rapidly on application of heat.
Answer 5
On Application of heat.force increases the K.E. of particles and space increases and inter-particle attraction decreases. Thus particles move rapidly.

Q.5. Complete the blanks with reference to inter conversion of matter on basis of kinetic theory-with the word ‘increase’, ‘decreases’, ‘gain’, ‘lose’ or ‘overcome’ in each case.

1. During melting of solids, the inter-particles space increases.
2. During vaporization, the liquid particles gain energy.
3. During liquefaction, the particles lose energy.
4. During solidification, the inter-particle space decreases gently.
5. During sublimation the inter-particle attraction is overcome.