Matter in Our Surroundings

Matter in our Surroundings
Class:IX / Unit:1

1. When a gas jar full of air is placed upside down on a gas jar full of bromine vapours, the red-brown vapours of bromine from the lower jar go upward into the jar containing air. In this experiment

Air is heavier than bromine
Bromine cannot be heavier than air because it is going upwards against gravity
Bromine is heavier than air
Both air and bromine have the same density

2. A form of matter has no fixed shape but it has a fixed volume. An example of this form of matter is

Carbon steel
Carbon dioxide
Kerosene
Krypton

3. Which one of the following statements is not true

The molecules in a solid vibrate about a fixed position
The molecules of a gas occupy all the space available
The molecules in a gas exert negligibly small forces on each other, except during collisions
The molecules in a liquid are arranged in a regular pattern

4. The correct procedure of heating iron-sulphur mixture to prepare iron sulphide is

Heat the iron filings-sulphur mixture at 3/4 quarters of the test tube using a red flame throughout
Heat the powder mixture at the base of the test tube using a blue flame throughout
Heat the iron filings and sulphur mixture in the middle of the test tube using yellow flame throughout
Heat the powder mixture at the top of the test tube using an orange flame throughout

5. When water at 0°C freezes to form ice at the same temperature of 0°C, then it

Absorbs some heat
Absorbs exactly 3.34 x 105J/kg of heat
Neither absorbs nor releases heat
Releases some heat

37. Why do trees acquire more leaves during summer ?
Answer: During summer, trees need to keep them cool by more transpiration. Leaves are the Location for transpiration that's why trees aquire more leaves for more transpiration.

38. Why do we feel comfortable under a fan when we are perspiring ?
Answer: Wefeel comfortable under a fan because air from fan helps in evaporation of sweat from our body and we feel cool and comfortable.

39. Why do people sprinkle water on the roof after a hot sunny day ?
Ans. People sprinkle water on the roof becouse it provides a cooling effect by causing evaporation. The water molecules absrorb heat from surrounding and changes to vapour and hence cause cooling effect.

40. Sponge, though compressible, is a solid ?
Answer: Solids have less compressibility but sponge can be compressed easily due to presence of air spaces. In these air spaces, air is filled .When we apply force, air is expelled out and sponge can be compressed and again after removal of force it regain its shape.

41. Under what conditions gases can be liquefied ? In which form LPG is filled in gas cylinder ?
Ans. Gases can be liquified by applying pressure and by reducing temperature.
LPG is filled in liquid state.

42. Liquid generally have lower density as compared to solids, but ice floats on water. Find out, why.
Answer: This is due to open cage like structure of ice . When water freezes to ice volume increases so, density decreases and hence ice floats.

43. Give reason to explain why it takes longer time to dry wet clothes in humid weather ?
Answer: In humid weather, there is already plenty of water present in air so, air will not take as much water as it takes on hot day Therefore, rate of evaporation will slow down and hence it takes longer time to dry wet clothes in humid weather.

44. Why mixture does not have a fixed melting point or a fixed boiling point? Give reason.
Answer: Mixtures don't have fixed composition of various components So, they don't have sharp or fixed melting and boiling points.

45. On suffering from fever which will lower down your body temperature, more ice or ice cold water ?
Answer: Ice will lower down body temperature more because of latent heat of fusion . Ice will absorb more heat from the body and hence can be used effectively.