CHEMISTRY [2 Mark Question Answer]

1. The composition of air varies from place to place and from time to time.
2. The components of air retain their individual properties.
3. Liquid air has no definite boiling point.
4. No energy exchange occurs when the components of air are mixed with each other.

1. Painting with red lead.
2. Oil paint is applied on doors and windows.
3. Enamel coating. Enamel is a mixture of iron, and steel with silicates.
4. Coal tar it is used for coating the lower parts of ships and bridges.

1. Oxygen is used by firemen, miners, aviators, sea divers and even by every living being.
2. Oxygen is necessary for burning of fuels.
3. Oxygen mixed with hydrogen as fuel produces.a flame with a very high temperature about 2800°C.
4. As a fuel in spacecraft.

1. Spontaneous oxidation
2. Rapid oxidation
3. Slow oxidation

Out of the above said three types, rapid oxidation produces large amount of heat and light energy.

1. Oxygen is only slightly soluble in water. Therefore, it can be collected over water without fear of excessive dilution.
2. Oxygen is slightly heavier than air, so it cannot be collected over air.

1. Donot collect the first-few bubbles of the gas produced as it is the air in the delivery tube which is driven out
2. Method of collection of gas should be appropriate Arundeep’s M.S. Chemistry-7th 126
3. Keep all inflammable and bummg apparatus away as oxygen is j a supporter of conbustion.

1. Helium :It is used for filling weather observation balloons.
2. Argon :It is used for filling electric bulbs at low pressure.
3. Neon :It is used for making advertising glow tubes, used on big shops, hotels etc. at night.

1. Presence of water vapour in air determines the climatic conditions. Excessive water vapour causes rain. They also produce snow, fog, mist, hails and other phenomenon, depending upon the temperature.
2. The presence of water vapour controls the rate of evaporation from the plants and animals.
3. The presence of water vapour is very essential for the growth of plants.
4. It is very essential for the health and comfort of animals.

1. In the thermal power plants, steel plants etc., electric precipitators should be used to reduce the smoke and ash entering the air.
2. Efficient internal combustion engines should be used in vehicles.
3. Improved chulha or stoves should be used to minimise the production of smoke and carbon-monoxide.
4. We must grow more trees as they absorb harmful gases.

1. Large amount of coal burnt in thermal plants throw out huge amounts of smoke and ash in the atmosphere.
2. Vehicles using petrol or diesel give out a lot of smoke and harmful gases like carbon-dioxide, lead, carbon- monoxide.
3. Burning of garbage causes a lot of pollution due to the formation of carbon-monoxide, sulphur dioxide and nitrogen dioxide.
4. Pesticides spread in the fields also cause air pollution.

• During forest fire, a large amount of carbon particles (smoke) and carbon-monoxide pollute the air.
• When volcanoes erupt, a huge amount of ash and sulphur-dioxide is added in the air as pollutants.

1. Variable composition at different places
2. Lacks distinct properties of its own
3. Has no definite boiling point
4. Components of air cannot be easily separated by physical means.
5. Formation of air does not involve any energy change.
6. Cannot be represented by a chemical formula.

1. Photosynthesis by green plants
2. Combustion of various compounds
3. Respiration by living organisms
4. Plants- during photosynthesis.

1. Provides moisture for plant and animal growth.
2. Determines climatic conditions by providing rain, snow, mist etc.
3. Prevents undue drying up of the plant and animal bodies.

1. nitrogen
2. oxygen
3. carbon dioxide
4. water vapour
5. inert or noble gases

1. fire
2. air
3. wood
4. earth

1. Oxygen is a colourless, odourless and tastless gas.
2. Under laboratory conditions, oxygen is practically insoluble ip water.
3. Oxygen is slightly heavier than air.
4. Under high pressure and low temperature, oxygen can be changed to liquid state. Liquid oxygen is slightly bluish in colour.

1. The white crystals of potassium nitrate slowly melt to form a colourless liquid.
2. The glowing splint bursts into flame, showing that molten potassium nitrate gives off oxygen gas.

1. Galvanising– iron metal is coated with zinc.
2. Enamelling– iron surface is baked with mixutre of silicates at high temperature.
3. Coating with red lead oxide paint or tar on iron surface.
4. Oils and grease coating on iron surface cuts off moist air and prevents rusting.

• It rekindles glowing wooden splinter.
• If mixed with colourless nitric oxide gas, it forms reddish brown fumes of nitrogen dioxide.
• It dissolves in alkaline pyrogallol solution and turns it brown.