A substance has no mass. Can we consider it as matter?
Ans. No, matter must have mass and occupy space.
Select the substances from the following which do not have the property of sublimation:
Camphor, Potassium permanganate, Copper sulphate, Naphthalene.
Ans. Potassium permanganate and copper sulphate do not have the property of sublimation.
Evaporation causes cooling. Why? Ans. Evaporation needs heat energy which it takes from surrounding and leads to degrees in temperature, i.e cooling take place.
Convert 300 K into Celsius scale and –10°C into Kelvin scale.
Ans.
(i) 300 K – 273 = 27°C
(ii) –10°C + 273 = 263 K
Name the property of gases due to which it is possible to fill CNG in cylinders for using as fuel in cars.
Ans. Gases can be easily compressed.
Rubber band changes its shape. Is it solid?
Ans. Yes, it is solid because it regains its shape.
Does evaporation cause a physical change or a chemical change?
Ans. Evaporation is a physical change.
List any two properties of particles of matter.
Ans.
(i) There is space between particles of matter.
(ii) The particles of matter are extremely small in size which cannot be seen even with a powerful microscope.
Give reasons to explain why it takes longer to dry wet clothes in humid weather?
Ans. It is because air is already saturated with water vapours therefore it will not be able to hold more water vapours easily.
Convert 370 K into Celsius Scale (°C).
Ans. 370 K – 273 = 97°C
Arrange three states of matter in the increasing order of rate of diffusion. Ans. Rate of Diffusion : Solids < Liquids < Gases
How does spreading of wet clothes quicken their drying? Explain.
Ans. It increases exposed surface area due to which water gets evaporated at faster rate.
What is dry ice? What happens when the pressure under which it is stored is decreased to 1 atmosphere? Ans. Dry ice is solid carbon dioxide. If pressure is decreased it will change into vapours.
With which name is the phenomenon of changing of a liquid into its vapours at temperature below its boiling point known? Ans. Sublimation.
The melting points of three solids X, Y and Z are 298 K, 314 K and 398 K respectively. Arrange these in increasing order of their inter particle force of attraction. Ans. X < Y < Z is the order of increasing inter particle attraction. Higher the force of attraction, higher will be melting point.
What is full form of CNG? Mention its one property which makes it so important. Ans. Compressed Natural Gas. It does not create pollution on combustion, it is clean fuel which makes it so important.
Write one important characteristic property of particles of matter. Ans. Particles of matter attract each other.
When camphor is heated in a China dish, it changes into gas without changing into liquid. What is the name given to this change of state? Ans. Sublimation.
Sponge is solid but still it can be compressed. Why? Ans. Sponge has pores which has air, therefore, it can be compressed.
Why is the temperature remain constant during sublimation? Ans. It is because heat of vaporisation and fusion overcome the force of attraction between particles.
What is evaporation? Ans. It is process of converting liquid into vapours.
When a solid melts, its temperature remains constant, so where does the heat energy go? What is the name given to this heat? Ans. The heat energy is used to overcome intermolecular force of attraction. It is called latent heat of fusion.
Convert the following thermometer readings into kelvin –100°C, 200°C. Ans.
–100°C + 273 = 173 K
200°C + 273 = 473 K
Why is light not considered as a matter? Ans. It is because it does not occupy space.
Is smell of clove or cardamom a matter? Ans. No, because it does not have mass and does not occupy space.
What happens to the boiling point of a liquid when atmospheric pressure decreases? Ans. Boiling point of liquid is the temperature at which its vapour pressure becomes equal to external pressure (atmospheric pressure).
Thus, when atmospheric pressure decreases, boiling point of liquid also decreases.
What are heterogeneous mixtures? Ans. Those mixtures whose composition is not same throughout are called heterogeneous mixtures, e.g. sulphur powder and iron filings.
Why mixture does not have a fixed melting or a fixed boiling point? Give two reasons. Ans.
(a) It does not have fixed composition.
(b) It does not have uniform ordered arrangement of particles.
When common salt is dissolved in water, what will be the change in volume and why? Ans. There is no change in volume. It is because common salt particles occupy the spaces between molecules of water.
Write one similarity between three states of matter.
Ans. All the three states of matter are made up of particles.
What is tincture of iodine?
Ans. A solution of iodine in alcohol is known as ‘tincture of iodine’.
On suffering from fever which will lower down your body temperature more, ice or ice cold water? why? Ans. Ice will lower down body temperature more because it will take heat of fusion from our body and feed fever will come down faster.
Define latent heat of vaporisation.
Ans. Latent heat of Vaporisation. It is defined as heat required to convert 1 kg of liquid into vapours completely at its boiling point.
People sprinkle water on open ground or roof on a hot sunny day. Why? Ans. It is because water gets evaporated by taking heat from surface of roof or ground and causes cooling.
Give reason : During summer sitting under a fan makes us comfortable. Ans. Fan takes hot air up and cold air comes down which makes us comfortable. It also helps in evaporation of sweat which causes cooling.
