Important Questions for Class 9 Chapter 1 - Matter in Our Surroundings

Important questions based on NCERT syllabus for Chapter 1 - Matter in Our Surroundings:

Question-1: Water stays cool in an earthen pot (matki) during summer. Why?
What will happen if this earthen pot is painted from the outside?

Solution: When the water oozes out of the pores of an earthen pot, during the hot summers, it begins to evaporate rapidly. Water molecules source latent heat of vapourisation from the water inside to achieve this purpose. This heat energy transfer causes the water contained in the pot to cool down.

If the earthen pot is painted from outside, the pores on the outer surface will get covered. This will disable the seeping water to come into direct contact with the dry air. Vapourisation will not take place as water will not be able to escape into the atmosphere. Hence the water will not be able to cool down fast.

Question-2: What are the characteristics of the molecular structure of gas?

Solution: 1. The intermolecular spaces are 1000 times or more than the liquids.This large intermolecular space weakens the intermolecular forces to almost negligible magnitude.
2. The molecules of a gas are free to move about in any direction.
3. This accounts for the fact that gases have no definite shape or volume and occupy all the available space.
4. Largest intermolecular space when compared to the other two physical states that is solids and liquids.
5. They are easily compressible.

Question-3: What are the full forms of CNG and LPG? Write their uses?

Solution: CNG stands for Compressed Natural Gas which is methane stored at high pressure. CNG is used in motor vehicles as an alternative fuel in place of Gasoline (Petrol), Diesel fuel and propane/LPG. CNG combustion produces fewer undesirable gases than these fuels.

LPG stands for Liquefied petroleum gas. It consists of gases like propane or butane which are flammable mixtures of hydrocarbon gases. LPG is used as fuel in heating appliances, cooking equipment, and vehicles. When specifically used as a vehicle fuel it is referred to as an autogas.