Case Study Based Questions: Combustion & Flame | Science Class 8 PDF Download

Case Study

The air that we breathe today is more polluted than it was before. More factories more vehicles greater use of aerosols and sprays, increasing number of refrigerators and air conditioners that release CFC gases, have all contributed toward pollution. When certain chemicals from the smoke and fumes rise up into the air they mix with the water vapour in the clouds and make it acidic. When rain or snow falls from such polluted clouds, it is also acidic in nature. This acidic rain falls on the leaves of trees, on the fertile soil and also runs into lakes and rivers. The effects of the rain are disastrous. Trees slowly lose their leaves and die. Fertile soil turns acidic and damages the plants and crops. The fish and animals living in lakes or seas are killed. Even our drinking water can be affected. Many forests all over the world have suffered severe damage on account of acid rains. Before it is too late, we must try and put a stop to the millions of vehicles and chimneys pouring harmful fumes into the air.

Q1: Which gas is released by the incomplete combustion of fuels?
(a) Oxygen
(b) Hydrogen
(c) Carbon monoxide
(d) None of the above
Ans: (c)
Sol: Carbon monoxide is a poisonous gas, which is produced by the incomplete combustion of fuels.

Q2: Emissions of sulphur dioxide and nitrogen oxide cause:
(a) Pollution
(b) Acid rain
(c) Deforestation
(d) None of the above
Ans: (b)
Sol: Acid rains are caused by emissions of sulphur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acid. It has a very harmful effect on plants, land and aquatic animals, and infrastructure.

Q3: What is the fire triangle?
Ans: For the generation of fire, we need three things to be present simultaneously:

• Some sort of fuel or combustible material.
• A heat source to raise the temperature of the fuel to its ignition temperature.
• Enough oxygen to sustain combustion.

If we remove any one of these resources, the fire can be controlled.

Q4: How is carbon dioxide responsible for global warming?
Ans: Molecules of carbon dioxide gas have a tendency to absorb heat. The carbon dioxide molecules present in the atmosphere absorb this heat energy and do not allow it to escape into space. Therefore, the more carbon dioxide molecules in the atmosphere, the higher the temperature, which eventually causes global warming.