NCERT Solutions class 9 Science 1. Matter in Our Surroundings Questions-Answers

Questions: NCERT Text Book/Chapter -1 /Page No.- 3

 

Q1. Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.

Ans : Chair, air, almonds, cold drink are matter.

Q2. Give reasons for the following observation:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

Ans : It is the property of matter that increasing the temperature, the particles of matter spread very faster. Thus the smell of hot food spread faster than cool food.

Q3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Ans : This observation shows that the particles of matter have space between them.

Q4. What are the characteristics of the particles of matter?

Ans: The characteristics of the particles of matter are the following.

1. Particles of matter have space between them.
2. Particles of matter are continuously moving.
3. Particles of matter attract each other.

Questions: NCERT Text Book/Chapter -1 /Page No.- 6

Q1. The mass per unit volume of a substance is called density. (density = mass/volume).

Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.

Ans : air, exhaust from chimneys, cotton, water, honey, chalk, iron

Q2.        

(a) Tabulate the differences in the characterisitcs of states of matter.

Ans :

Solid:

1. Solid have a definite shape.
2. Solid have a fixed volume.
3. It cannot be changed its shape.
4. Inter molecular force are strongest in solid.

Liquid;

1. Liquids have no fixed shape.
2. Liquids flow and change shape so they are not rigid.
3. They are not compressed.
4. Inter molecular force are less strong in liquids.

Gas:

1. Gases neither have a definite.
2. They can do compressed.
3. Gas can also flow.
4. Inter molecular force are large space than solid and liquid.

(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Ans :

1. Rigidity - Rigidity is the property of solid. It means unbending (hardness). It cannot be changed its shape.                          
2.  Compressibility – The particles of matter have space between them. So the gases have more compressibility.
3. Fluidity – it is a property of matter. In which matters spread on the surface.
4. Filling a gas container – The state of matter which has a space between particles and property of compressibility that fills a gas container completely.
5. Shape – Shape is a physical view of matter in which they acquire their size.
6. Kinetic energy and density – having kinetic energy the states of matter in increasing order such as solid, liquid and gas has more kinetic energy. But in density solid is most than other and gas is lowest than all.

Q3. Give reasons;

(a)  A gas fills completely the vessel in which it is kept.

Ans : Due to its high compressibility, a gas fills completely the vessels in which it is kept.

(b)  A gas exerts pressure on the walls of the container.

Ans :  gases show the property of diffusing very fast into other gases. In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container.

(c)  A wooden table should be called a solid.

Ans : A wooden table has the properties of a definite shape, fixed volume and intermolecular space is strong, so it should be called a solid.

(d) 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 intermolecular space between the particles of air is more and therefore intermolecular force is too weak so we can easily move our hands in air. Whereas intermolecular space in solid is very strong so we need a karate expert. 

Q4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Ans: The particles of ice far away from each other while water is stronger due to hydrogen bonding. So the volume of ice is more and density is less. This make ice to float on water.

Questions: NCERT Text Book/Chapter -1 /Page No.- 9

Q1. Convert the following temperature to celsius scale:

1.  300 K
2.  573 K.

Ans :  { changing in Celsius scale 273 is subtracted form given Kelvin value}

1. 273 k = 0^oC

300 k – 273 = 27^o C                

Hence 300k = 27^o C

1. 573 k – 273 = 300^o C

Hence 573k = 300^o C

Q2. What is the physical state of water at:

1. 25 ºC
2. 0ºC
3. 100ºC

Ans :     

1. Water is liquid at 25^oC.
2. Water is solid at 0^oC.
3. Water is gas at 100^oC.

Q3. For any substance, why does the temperature remain constant during the change of state?

Ans : because the heat supply is used up in changing the state by overcoming the force of attraction between the particles.

Q4. Suggest a method to liquefy atmospheric gases.

Ans : To liquefy atmospheric gases we apply pressure and reduce temperature.

Questions: NCERT Text Book/Chapter -1 /Page No.- 10

Q1. Why does a desert cooler cool better on a hot dry day?

Ans : On a hot day temperature is higher. This temperature increases the rate of evaporation cause better cooling by desert cooler. 

Q2. How does the water kept in an earthen pot (matka) become cool during summer?

Ans : an earthen pot (matka) has many fine pores in it through which evaporation takes place and it absorbs heat from outside of Matka this causes increasing rate of evaporation resulting in cooling water.

Q3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Ans : When we put some acetone or petrol or perfume on our palm it spread over palm in a large area. We know evaporation increases due to increasing surface area. It gains energy and gets evaporated cause cooling.

Q4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Ans : The surface area of saucer is more than the surface area of cup. The rate of evaporation is faster in saucer and therefore, cooling is also faster than cup.

Q5. What type of clothes should we wear in summer?

Ans : we should cotton clothes during summer season. 

Exercise: NCERT Text Book/Chapter -1 /Page No.- 12 

Q1. Convert the following temperatures to the Celsius scale.

(a)   300 K        

(b)    573 K.

Ans :  { changing into Celsius scale 273 is subtracted form given Kelvin value}

273 k = 0^oC

300 k – 273 = 27^o C

Hence 300k = 27^o C

573 k – 273 = 300^o C

Hence 573k = 300^o C

Q2. Convert the following temperatures to the Kelvin scale.

(a)     25°C          

(b)     373°C.

Ans:    { changing into keivin scale 273 is added to given Celsius value}

273 k = 0^oC

(a) 25°C = 25 + 273 K

   = 298 k

(b) 373°C. = 373 + 273 K

    = 646 K

Q3. Give reason for the following observations.

(a)  Naphthalene balls disappear with time without leaving any solid.

Ans : Naphthalene is a sublimely agent which get sublimed and change directly from solid to gas. Hence   Naphthalene balls disappear with time without leaving any solid.

(b)  We can get the smell of perfume sitting several metres away.

Ans : It is due to diffusion. The particles of perfume move at random motion in all directions and mix with air molecules so We can get the smell of perfume sitting several metres away.

Q4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.

Ans :  sugar, water, oxygen.

Q5.  What is the physical state of water at—

(a)     25°C  

(b)    0°C    

(c)    100°C 

Ans :     

1. Water is liquid at 25^oC.
2. Water is solid at 0^oC.
3. Water is gas at 100^oC.

Q6. Give two reasons to justify—

(a) water at room temperature is a liquid.

Ans :  The room temperature is less than the boiling point of water and more than the temperature at this solidifies. Therefore water is liquid at room temperature.

(b) an iron almirah is a solid at room temperature.

Ans :  The room temperature is not more than the its melting point. While melting point of iron is much higher. So an iron almirah is a solid at room temperature.

Q7.  Why is ice at 273 K more effective in cooling than water at the same temperature?

Ans : water at 273 k takes heat during increasing in temperature but do not change it state but ice at same temperature takes heat and changes its state due to this ice is more effective in cooling than water at the same temperature

Q8. What produces more severe burns, boiling water or steam?

Ans : Steam , it boils at 373 K and has more quantity of heat due to its gaseous form it has more compression than the liquid form of water.