Class 9 Science Chapter 1 Case Based Questions - Matter in Our Surroundings

(I) Read the given passage and answer the questions that follows based on the passage and related studied concepts.
Matter is anything that occupies space and has mass. Matter is classified into solid, liquid and gas. In solid state particles are closely packed and have very strong force of attraction, particles can only vibrate and rotate around fixed positions. In liquid state, particles are less closely packed and have strong force of attraction but less than solids, particles can move throughout the liquid.
In Gaseous state, particles are far apart with weak force of attraction and are in state of constant random motion. Gases can be easily compressed where as solids and liquids are incompressible.
Q1: An inflated balloon is placed in refrigerator, what will happen?
(a) Balloon will shrink and particles will move faster and become closer.
(b) Balloon will expand and particles will move faster and become far apart.
(c) Balloon will shrink, particles will move slower and become close together.
(d) Balloon will expand, particles will move slower and come closer therefore, volume of balloon will decrease.
Ans: (c) Balloon will shrink, particles will move slower and become close together.

When an inflated balloon is placed in the refrigerator, the temperature decreases. This causes the gas particles inside the balloon to move slower and come closer together, resulting in the balloon shrinking. 

Q2: When solid changes into vapours, the process is called.
(a) Evaporation
(b) Boiling
(c) Sublimation
(d) Vapourisation
Ans: (c)

Sublimation is the process by which a solid changes directly into a gas without passing through the liquid state.

Q3: A substance melts at 5°C and boils at 150°C. What will be its physical state at room temperature? 
Ans: Room temperature (around 25°C) is between the melting point (5°C) and the boiling point (150°C) of the substance. Therefore, the substance will be in the liquid state at room temperature. 

Q4: Why do we feel more cold after taking bath with hot water?
Ans: We feel more cold after taking a bath with hot water because when we step out of the hot water, the water on our skin starts to evaporate. The evaporation process requires heat, which is taken from our body, causing a cooling effect and making us feel colder. 

(II) Boiling occurs when the particles in a liquid state absorb enough energy to overcome the forces holding them together and begin to move apart to form a gas. A liquid is being heated, a graph is plotted between time and temperature in °C. Answer the questions based on graph.
Q1: What does OA represent?
Ans: It represents liquid is being heated and absorbing energy, therefore, particles move more energetically.

Q2: What does AB represent?
Ans: It represents a mixture of liquid and vapours at the boiling point of the liquid.

Q3: Why does temperature remain constant at boiling point?
Ans: The temperature remains constant at the boiling point because the heat of vaporization is used to overcome the force of attraction between liquid particles.

Q4: What does BC represent?
Ans: It represents a vapour state, and particles absorb heat and become more energetic. The temperature of the gas will rise.

(III) Read the following information and answer the questions based on information and related studied concepts
Substance – 1. is brittle.
Substance – 2. melts at 5°C and boils at 150°C.
Substance – 3. has high melting point of 800°C.
Substance – 4. has melting point –169°C and boiling point –104°C.

Q1:  What is physical state of substance – 4 at –150°C and –100°C?
Ans:  

• At –150°C: Substance – 4 will be in the solid state.
• At –100°C: Substance – 4 will be in the gaseous state.

The melting point of Substance – 4 is –169°C, and its boiling point is –104°C. Therefore, at –150°C (which is above its melting point but below its boiling point), Substance – 4 will be a solid. At –100°C (which is above its boiling point), it will be a gas.

Q2: What is physical state of substance – 1 and 3 at room temperature?
Ans: 

• Substance – 1: The physical state cannot be determined solely based on the information that it is brittle. However, substances that are brittle are often solids at room temperature.
• Substance – 3: Solid.

Substance – 1: Brittle substances are typically solid (e.g., certain metals, minerals, and salts).

Substance – 3: With a high melting point of 800°C, it will be in the solid state at room temperature (~25°C).

Q3: What is physical state of substance – 2 at 100°?
Ans: It will be in a liquid state.

The melting point of Substance – 2 is 5°C, and its boiling point is 150°C. Therefore, at 100°C, Substance – 2 will be in the liquid state.

Q4: Out of substances – 1, 2, 3, 4 which one has strongest force of attraction?
Ans: Substance 3 has strongest forces of attraction.

The strength of the force of attraction between particles can be inferred from the melting point. Substance – 3 has the highest melting point (800°C), indicating that it has the strongest force of attraction between its particles.