Punjab State Board PSEB 9th Class Science Book Solutions Chapter 1 Matter in Our Surroundings Textbook Exercise Questions and Answers.
PSEB Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings
PSEB 9th Class Science Guide Matter in Our Surroundings Textbook Questions and Answers
Question 1.
Convert the following temperature to the Celsius scale:
(a) 293 K
(b) 470 K.
Answer:
(a) 293 K = 293 – 273 = 20°C
(b) 470 K = 470 – 273 = 197°C
Question 2.
Convert the following temperatures to the Kelvin scale:
(a) 25°C
(b) 373°C.
Answer:
(a) 25°C – 25 + 273 = 298 K
(b) 373°C = 373 + 273 = 646 K
Question 3.
Give reason for the following observations:
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Answer:
(a) This is because naphthalene sublimes i.e. it directly changes into vapour without melting.
(b) This is because the molecules of perfume are moving with very high velocities (i.e. diffusion) in all the directions.
Question 4.
Arrange the following substances in increasing order of forces of attraction between the particles-water, sugar, oxygen.
Answer:
The increasing order of intermolecular forces of attraction is Oxygen < Water < Sugar.
Question 5.
What is the physical state of water at:
(a) 25°C
(b) 0°C
(c) 100°C?
Answer:
(a) At 25° C, water is liquid.
(b) At 0° C, water is solid (Ice).
(c) At 100° C, water is gas (Steam).
Question 6.
Give two reasons to justify that:
(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.
Answer:
(a) At room temperature water is liquid because the attractive forces between the molecules of water are small and can move from one point to another.
(b) An iron almirah is solid because the molecules are held together by strong intermolecular attractive forces and the molecules or particles are very close to each other.
Question 7.
Why is ice at 273 K more effective in cooling than water at the same temperature ?
Answer:
Ice at 273 K is more effective in cooling than water at 273 K, this is because in ice, the molecules have lower energy as compared to the particles in the liquid water at the same temperature (273 K) and require latent heat of fusion for melting.
Question 8.
What produces more severe bums: boiling water or steam?
Answer:
Steam produces severe burns as compared to boiling water. This is because in steam the molecules have higher kinetic energy than in boiling water.
Question 9.
Name A, B, C, D, E and F in the following diagram showing state change-
Answer:
A – Fusion
B – Vaporisation
C – Condensation
D – Solidification
E – Sublimation
F – Sublimation
Science Guide for Class 9 PSEB Matter in Our Surroundings InText Questions and Answers
Question 1.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Answer:
Chair, air, almonds, cold drink, smell of perfume.
Question 2.
Give reasons for the following observations:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer:
The smell of hot sizzling food reaches us several metres away, but to get the smell from cold food we have to go close. This is because the rate of diffusion of a gas increases with the increase in temperature. In hot food, the rate of diffusion is large but in cold food, the rate of diffusion is slow.
Question 3.
A diver is able to cut through water in a swimming pool, which property of matter does this observation show?
Answer:
The diver is able to cut through water in a swimming pool because in water the attractive forces between the molecules are small.
Question 4.
What are the characteristics of the particles of matter?
Answer:
The characteristics of the particles of matter are:
- The particles of matter have vacant spaces between them.
- The particles of matter are always in motion.
- There are attractive forces between the particles of matter.
Question 5.
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.
Answer:
The increasing order of density is
Exhaust from chimneys < air < cotton < chalk < honey < iron.
Question 6.
(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following:
rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Answer:
(a) Differences in the characteristics of states of matter:
| Characteristics | Solid | Liquid | Gas |
| 1. Vacant spaces | Very small | Small | Very large |
| 2. Attractive forces between particles | Very large | Small | Negligible |
| 3. Compressibility | Negligible | Low | High |
| 4. Rigidity | High | Low | Not rigid |
| 5. Density | High | Low | Very Low |
| 6. Energy | Small | Large as compared to solid | Very high |
(b) Rigidity: It is the property by virtue of which a substance can retain its shape when a force is applied to it. Solids possess the property of rigidity.
- Compressibility: The property by virtue of which the volume of a substance can be decreased by applying force or pressure on it. Gases have high compressibility because of large vacant spaces between the molecules of a gas.
- Fluidity: It is the property by virtue of which the molecules of one substance can flow from one point to another. Liquids and gases possess fluidity.
- Filling a gas container: A gas fills the container because there are negligible attractive forces between the molecules of a gas and the molecules of a gas move with very high velocities in all possible directions.
- Shape: It is the definite geometrical arrangement of constituent particles of a substance. Solids have definite shapes.
- Kinetic energy: It is the energy possessed by a particle due to its motion.
- Density: Density of a substance is the mass per unit volume. Its units are g/cc or kg/m3.
Question 7.
Give reasons:
(a) A gas fills completely the vessel in which if is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same in solid block of wood we need a Karate expert.
Answer:
(a) This is because in a gas the attractive forces between the molecules are negligible and molecules of a gas move with very high speeds in all possible directions.
(b) This is due to the hits or bombardments of the molecules of a gas against the walls of a container.
(c) This is because it has a definite mass, volume and shape.
(d) This is because in air, the attractive forces between the particles are negligible but in a solid block of wood, there are large attractive forces between the constituent particles.
Question 8.
Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Answer:
Ice floats over water because ice has lower density than liquid water. This is because in ice for a given mass volume is more as compared to in liquid water.
Question 9.
Convert the following temperature to Celsius scale:
(a) 300 K
(b) 573 K?
Answer:
(a) 300 K = 300 – 273 = 27°C.
(b) 573 K = 573 – 273 = 300°C.
Question 10.
What is the physical state of water at:
(a) 250°C
(b) 100°C?
Answer:
(a) Gas
(b) Gas
Question 11.
For any substance, why does the temperature remain constant during the change of state?
Answer:
This is because the heat supplied is used to overcome the attractive forces between the particles i.e., there is change in potential energy.
Question 12.
Suggest a method to liquefy atmospheric gases.
Answer:
The atmospheric gases can be liquefied by cooling under pressure.
Question 13.
Why does a desert cooler cool better on a hot dry day?
Answer:
On a hot dry day due to increase in temperature and lesser humidity the evaporation of water will be faster.
Question 14.
How does the water kept in an earthen pot (matka) become cool during summer?
Answer:
This is because the water comes out from the pores of earthen pot (matka) and it evaporates. Due to evaporation it causes cooling.
Question 15.
Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer:
This is because the particles of acetone or petrol or perfume gain energy from our palms and surroundings and evaporate causing cooling.
Question 16.
Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer:
Because a saucer provides more surface area than a cup for evaporation of liquid into vapour and it causes a more cooling effect.
Question 17.
What type of clothes should we wear in summer?
Answer:
White cotton clothes.
