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CNMS ICSE - 7 Std
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Chapter: 07. Air And Atmosphere

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Why does acid rain reduce soil fertility?
Acid rain reduces soil fertility by making the soil highly acidic, which directly impairs plant growth and destroys vital nutrients.
Why is liquid nitrogen used in the food industry?
Liquid nitrogen is used as a refrigerant for the rapid freezing of food items.
What are the approximate percentages of oxygen in the air by volume and by mass?
Oxygen constitutes 21% of air by volume and 23.2% of air by mass.
What is the chemical difference between fast oxidation and slow oxidation?
Fast oxidation is a rapid reaction releasing both heat and light energy (such as burning), whereas slow oxidation takes place gradually and releases minimal heat with no light energy (such as respiration).
What is the approximate percentage of carbon dioxide present in the atmosphere?
Carbon dioxide makes up approximately 0.03% of the air by volume.
What is the function of putrefying bacteria and fungi in the nitrogen cycle?
Putrefying bacteria and fungi break down animal waste and dead proteins into ammonium compounds through the process of ammonification.
How does respiration differ from combustion regarding temperature?
Respiration occurs naturally at body temperature (37°C), whereas combustion is an artificial process that occurs only at much higher temperatures.
What is the ratio of nitrogen and oxygen in air by volume as concluded from Lavoisier’s experiment?
Lavoisier’s experiment concluded that the ratio of nitrogen and oxygen in air is 4:1 by volume.
What are noble gases, and which is the most abundant one in our air?
Noble gases are chemically inert gases present in traces in the air, with argon being the most abundant of them.
How can oxygen be prepared on a large scale from water?
Oxygen is prepared on a large scale by passing an electric current through acidulated water to decompose it into hydrogen and oxygen.
What observations are made when sulfur is burnt in a jar of oxygen and tested with blue litmus?
Sulfur burns with a brilliant blue flame to produce sulfur dioxide gas, which dissolves to turn the blue litmus solution red, indicating its acidic nature.
Why does lime water turn milky when air from an air pump is blown through it?
Limewater turns milky because carbon dioxide in the blown air reacts with calcium hydroxide to form an insoluble white precipitate of calcium carbonate.
How is nitrogen fixed in nature during lightning?
At the high temperatures of lightning, nitrogen and oxygen react to form nitric oxide, which further oxidizes to nitrogen dioxide and reacts with water vapour to form nitrous and nitric acids that reach the soil as nitrates.
What is particulate matter (PM) and why is it dangerous?
Particulate matter is a mixture of tiny solid particles or liquid droplets suspended in the air that can bypass respiratory defenses and cause severe lung and heart problems.
Who was the first person to prepare oxygen gas, and how was it done?
Carl Wilhelm Scheele was the first person to prepare oxygen gas in 1772 by heating mercuric oxide.
What is rust chemically, and what conditions are required for its formation?
Rust is chemically hydrated ferric oxide (
math
⁠
), and its formation requires the simultaneous presence of both oxygen and moisture.
Why does the composition of air vary between industrial cities and coastal areas?
The composition of air varies because the air in industrial cities has higher percentages of carbon dioxide and dust, while the air in coastal areas contains more water vapour.
Why is potassium chlorate avoided for the routine laboratory preparation of oxygen gas?
Potassium chlorate is avoided because it requires high temperatures that can crack glass apparatus and carries an explosion risk if combustible impurities are present.
In Lavoisier’s experiment, what name was given to the active portion of air that supported burning?
Lavoisier called the one-fifth active portion of air in the bell jar “active air,” which he later named oxygen.
Why does magnesium gain weight when it is burnt in a crucible?
Magnesium gains weight because it chemically combines with oxygen from the air to form solid magnesium oxide.
How does a catalytic converter help in preventing air pollution?
A catalytic converter is installed in automobiles to chemically convert harmful toxic exhausts into harmless gases before they are released.
Define nitrogen fixation.
Nitrogen fixation is the process of converting free atmospheric nitrogen into soluble nitrates that plants can easily absorb from the soil.
What is the biological importance of the process of photosynthesis?
Photosynthesis uses carbon dioxide and water in the presence of sunlight and chlorophyll to produce glucose and oxygen, thereby renewing the oxygen supply in the atmosphere.
Who proved that air is a mixture of many gases rather than a single substance?
The French scientist Antoine Lavoisier conducted experiments that proved air is a mixture of many gases.
Why is manganese dioxide added during the laboratory preparation of oxygen from hydrogen peroxide?
Manganese dioxide is added to act as a catalyst that speeds up the decomposition of hydrogen peroxide without being consumed itself.
State two physical properties of nitrogen gas.
Nitrogen is a colourless, odourless, tasteless, non-poisonous, and non-combustible gas that is slightly soluble in water.
What is precipitation in the context of the water cycle?
Precipitation is the process where condensed water vapour in the atmosphere falls back to the earth’s surface as rain, hail, snow, dew, or mist.
How does denitrification return nitrogen gas to the atmosphere?
Pseudomonas bacteria in the soil convert a portion of soil nitrates back into nitrogen gas, which then escapes into the atmosphere.
What is the primary role of nitrogen in the growth of living organisms?
Nitrogen is an essential component of proteins, vitamins, and nucleic acids, which are necessary for the growth and development of all living organisms.
What is the nature of the oxide formed when magnesium burns in oxygen?
Magnesium burns with a dazzling white flame to form magnesium oxide, which is basic in nature and turns red litmus solution blue.
How is oxygen gas separated from nitrogen gas during the fractional distillation of liquid air?
During fractional distillation, nitrogen gas boils off first at -195.5°C, leaving behind liquid oxygen which changes to gas at -183°C.
How does solid carbon dioxide act as an effective refrigerant?
Solid carbon dioxide, or dry ice, acts as a refrigerant because it sublimes directly from solid to gas, keeping food items cold and dry without melting.
How does oxygen gas affect a glowing wooden splinter?
A glowing wooden splinter bursts into a bright flame when introduced into a jar of oxygen gas, demonstrating that oxygen supports combustion.
What chemical reactions lead to the formation of acid rain?
Acid rain is formed when acidic oxides of sulfur and nitrogen in polluted air react with water vapour, oxygen, and other chemicals to produce sulfuric, sulphurous, nitric, and nitrous acids.
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