NCERT Solutions for class 9 Chemistry Matter in our surroundings

In-text question and answers

Q1: Give reason for why the smell of hot sizzling food reaches you several meters away, but to get the smell of cold food you have to go close?

Ans: Since the particles of matters are continuously moving and with the rise in temperature they move even faster (i.e they possess more kinetic energy). Hence, we’re able to get the smell of hot sizzling food several meters away.

Q2: A diver is able to cut through water is a swimming pool. Which property of matter does this observation show?

Ans: The particles of fluid (ex: water) are loosely packed; it means that they have more space between them. Hence, it becomes easy to cut through it. It shows the property of “Particles of matter have space between them”.

Q3: Tabulate the difference in the characteristics of state of matter.

Ans:

Property	Solid state	Liquid state	Gas state
Rigidity	Highly rigid	Less rigid	No rigidity
Shape	Definite shape	No fixed shape	No fixed shape
Volume	Fixed volume	Fixed volume	No fixed volume
Compressibility	None	High as compared to solids	Maximum
Intermolecular space	Less	More as compared to solids	Highest
Fluidity	Do not flow	Less flowable as compared to gas	Highest flowability
Density	High density	Less density as compared to solids	Very less density

 

*Density: The mass per unit volume is called density.

Q4: Comment on the following:

Rigidity: It defines the hardness of a matter.

Compressibility: The ability of a matter that allows to get compressed is called its compressibility.

Fluidity: The ability of a matter to flow is called fluidity.

Filling a gas container:

Q5: Give reasons

-> A gas fills completely the vessels in which it is kept

Ans: A gas has no fixed shape and volume. It has high inter-molecular space between its particles and less force of attraction, that is why a gas completely fill inside a vessel.

-> A gas exerts pressure on the walls of the container

Ans: The gas has the tendency to expand and it possess high kinetic energy that is why is exerts pressure on the walls of the container.

-> A wooden table should be called a solid

Ans: The wooden table is a solid because it has rigid shape, fixed size, and volume and has less compressibility.

-> We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert

Ans: The inter-molecular space in air and the force of attraction between its particles is less as compared to wooden block. Hence, we can easily move our hands inside air whereas to do the same we need a karate expert.

Q6: Convert the following temperature to Celsius scale:

(a)  300K

Ans: 300K – 273K = 27^oC

(b) 573K

Ans: 573K – 273K = 300^oC

Q7: For any substance, why does the temperature remain constant during the change of state?

Ans: After reaching certain temperature it becomes constant and doesn’t show any further rise even if we increase the heat because it is believed that the heat is hidden inside the vessel which is also known as latent heat of fusion.

Q8: Why does a desert cooler cool better on a hot dry day?

Ans: A desert cooler cools better on a hot dry day because the humidity is less on a dry day which increases the rate of evaporation that leads to faster and more cooling.

Q9: How does the water kept in an earthen pot become cool during summer?

Ans: Evaporation causes cooling. And in summer season,  the rate of evaporation increases, so when the hot air strike the walls of earthen pot it causes evaporation and leads to cooling of water.

Q10: Why we are able to sip hot tea or milk from the saucer rather than a cup?

Ans: The surface area of saucer is more as compared to cup, which leads to faster evaporation that cools the hot tea faster in saucer and slower in cup. Hence, we are able to  sip the hot tea or milk from the saucer rather than a cup.

Q11: What type of clothes should we wear in summer?

Ans: We should wear cotton clothes in summer season because they are better at absorbing the sweat of our body and when the hot air strike its surface the process of evaporation happens which leads to cooling and we feel better.

*Latent heat of fusion:

Latent heat of fusion is the amount of heat required to convert 1kg of a solid into liquid at its melting point.

*Latent heat of vaporization:

Latent of vaporization is the amount of heat required to convert 1kg of liquid into gas at its boiling point.

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