ICSE Solutions for Chapter 7 Air and Atmosphere Class 7 Chemistry Selina Publisher
A. Air: A Mixture of Gases
Exercise- I
1. Give one use for each of the following inert gases :
(a) argon
(b) helium
(c) neon
(d) radon
(e) krypton
(f) xenon
Answer
(a) Argon: Argon is filled into electric bulbs to prevent the oxidation of their filaments.
(b) Helium: It is used in filling up weather observation balloons.
(c) Neon: Neon is used for making advertisement sign boards.
(d) Radon: It is used for treatment of Cancer.
(e) Krypton: It is used in photography.
(f) Xenon: It is also used in photography.
2. Answer the questions put against each of the following constituents of air :
(a) Nitrogen : Explain its significance for plants and animals.
(b) Oxygen : What is the percentage proportion of oxygen in air ? Why is oxygen called active air.
(c) Carbon dioxide: “Although carbon dioxide plays no role in respiration, all life would come to an end if there is no carbon dioxide in air.” Support this statement with relevant facts.
(d) Water vapours: Explain their role in modifying the earth’s climate.
Answer
(a) Plants convert nitrogen into protein. It is an important constituent of proteins, which are necessary for the growth of animals, plants and human beings. Plants convert nitrogen into proteins.
(b) 20.9%, oxygen is called active air because it supports life on earth. It is essential for the process of combustion.
(c) Carbon dioxide is essential for photosynthesis by which green plants prepare their food. It minimises heat loss by radiation. Thus, it balances the temperature on earth.
(d) Water vapour determine the earth’s climate conditions. It causes rain. It controls the rate of evaporation from the bodies of plants and animals.
3. Define the following terms :
(a) pollutants
(b) acid rain
(c) Global warming
(d) smog
Answer
(a) Pollutants : Air contains substances which are harmful to plants and animals. These harmful substances are called pollutants.
(b) Acid rain : When sulphur trioxide and nitrogen oxide present in the air mix with rainwater they form sulphuric acid and nitric acid respectively. Rainwater containing these acids is called acid rain.
(c) Global warming : An increase in the percentage of carbon dioxide, methane, nitrous oxide and chlorofluorocarbon traps the heat causing the temperature of the earth and its surroundings to rise. This is known as global warming.
(d) Smog : Oxides of nitrogen form a mixture of smoke and fog known as smog which affects our eyes too.
4. “Air is a mixture”. Support this statement citing at least three evidences.
Answer
“Air is a mixture” The following are in evidences which prove that air is a mixture.
- The composition of air varies from place to place and from time to time.
- The components of air retain their individual properties.
- Liquid air has no definite boiling point.
- No, energy exchange occurs when the components of air are mixed with each other.
5. What is air pollution ? What are the harmful effects of sulphur dioxide, nitrogen dioxide and hydrogen sulphide present in the air ?
Answer
Air Pollution : Air is polluted by natural processes like volcanic eruption, crop pollination, etc. mostly it is polluted by human activities like burning of coal, wood, diesel oil, kerosene, petrol etc.
Fossil fuels contain sulphur and nitrogen as impurities. When fuels bum these substances combine with air to produce gasses like sulphur dioxide, nitrogen oxide and hydrogen sulphide. They cause many serious respiratory problems. They can destroy the ozone layer, which protects us from the ultra violet radiations of the Sun. They also cause acid rain, which damages crops and buildings.
6. (a) What are the causes of air pollution ?
(b) Suggest five measures to prevent air pollution.
Answer
(a) When fuels bum they produce sulphur dioxide, sulphur trioxide, nitrogen dioxide, hydrogen sulphide when these gases mix with rain water. They produce sulphuric and nitric acid. These acids mix with rain water to form acid rain.
(b) Five measures for the prevention of air pollution are:
- By using smokeless sources of energy, like solar energy and electrical energy, in place of conventional fossil fuels.
- By using filters for the. smoke coming out of the chimneys of factories and power plants.
- By using internal combustion engines in vehicles for complete and efficient burning of fuel.
- By locating industries away from residential areas.
- By growing more trees.
7. (a) What is nitrogen-fixation ?
(b) What are the two ways in which nitrogen fixation occurs?
(c) Explain the conversion of nitrogen into nitrates during lightning.
Answer
(a) Nitrogen fixation : Symbiotic bacteria living in the root nodules of leguminous plants like peas, beans, absorb nitrogen directly from air and convert into nitrates. Thereafter, the plants convert it into proteins. Nitrogen is returned to the soil when plant and animal matter decays. This decomposition work is done by organisms called denitrifying bacteria which reconvert dead organic tissue into its constituent nitrogen.
(b) 1. Natural process.
2. Non-biological fixation.
(c) During lightning, temperatures often reach as high as 3000°C. At such high temperatures, nitrogen and oxygen present in the air combine to form nitric oxide, which further react with oxygen to form nitrogen dioxide
B. Oxygen
Exercise- II
1. Name :
(a) The most abundant element in the earth’s crust.
Answer
Oxygen.
(b) A chemical called oxygenated water.
Answer
H2O2 (Hydrogen peroxide)
(c) A metal highly resistant to rusting.
Answer
Tin
(d) A mixture of oxygen and carbon dioxide used for artificial respiration.
Answer
Carbogen
(e) Two substances from which oxygen can be obtained at a large scale.
Answer
Air, water.
(f) An oxide and a carbonate containing oxygen.
Answer
Mercuric oxide and potassium chlorate.
(g) Two substances which undergo rapid oxidation.
Answer
Sodium, carbon.
2. (a) Taking hydrogen peroxide, how would you prepare oxygen in the laboratory ?
(b) What is the role of manganese dioxide in the preparation of oxygen ?
(c) Write the balanced chemical equation for the above chemical reaction.
(d) Why is hydrogen peroxide preferred in the preparation of oxygen gas ?
(e) Why is oxygen collected by downward displacement of water ?
(f) What happens when a glowing splinter is introduced in a jar containing oxygen ?
(g) What happens when oxygen gas is passed through alkaline pyrogallol solution ?
Answer
(a) Take manganese dioxide in a round bottom flask and add hydrogen peroxide drop by drop to it, which acts; a catalyst as shown in the figure. Collect oxygen by downward displacement of water.
2. The rate of evolution of oxygen (O2) is moderate and under control. H2O2 is a safe chemical.
(e) Since the water is displaced downward by the gas collecting in the jar, the process is called downward displacement of water. The reasons are :
- Oxygen is only slightly soluble in water. Therefore it can be collected over water without fear of excessive dilution.
- Oxygen is slightly heavier than air, so it cannot collected over air.
(f) Introduction of glowing splinter in the jar. The glowing splinter rekindles, but the gas does not catch fire.
(g) Alkaline pyrogallol solution turns brown when oxygen is passed through it.
3. (a) What happens when
i. mercuric oxide and
ii. potassium nitrate are heated ?
(b) Why is potassium chlorate not used for laboratory preparation of oxygen ?
Answer
(a) i. When mercuric oxide is heated, it decomposes to give mercury and oxygen.
ii. Potassium nitrate on heating gets converted into molten potassium nitrite with the release of oxygen.
(b) Potassium chlorate needs heating for quite sometime (to a high temperature) before it decomposes.
4. What are oxides ? Give two examples for each of metallic and non-metallic oxides.
Answer
Oxides are binary compounds formed by the chemical combination of a substance metal or a non-metal with oxygen.
Examples:
Metal:
- Sodium oxide (Na2O)
- Calcium oxide (CaO)
Non-metal:
- Sulphur dioxide (SO2)
- Carbon dioxide (CO2)
5. Name the three types of oxidation processes. In which of these large amount of heat and light energy are produced?
Answer
Oxidation can be categorised into three types :
- Spontaneous oxidation
- Rapid oxidation
- Slow oxidation
Out of the above said three types, rapid oxidation produces large amount of heat and light energy.
6. What do you observe when the following substances are heated and then tested with moist blue and red litmus – paper?
(a) Sulphur
(b) Phosphorus
(b) Calcium
(d) Magnesium
Answer
(a) Sulphur: Blue litmus turns red.
(b) Phosphorus: Blue litmus turns red.
(c) Calcium: Red litmus turns blue.
(d) Magnesium: Red litmus turns blue.
7. Complete and balance the following chemical equations.
- Oxygen is used by firemen, miners, aviators, sea divers and even by every living being.
- Oxygen is necessary for burning of fuels.
- Oxygen mixed with hydrogen as fuel produces a flame with a very high temperature about 2800°C.
- As a fuel in spacecraft.
- Painting with red lead.
- Oil paint is applied on doors and windows.
- Enamel coating. Enamel is a mixture of iron, and steel with silicates.
- Coal tar it is used for coating the lower parts of ships and bridges.
10. State two differences between : Rusting and burning.
Answer
Difference between rusting and burning
|
Rusting |
Burning |
|
1. Rusting is the process in which iron slowly reacts with oxygen in the air and produces a flaky substance called rust. 2. Air and moisture are necessary for rusting. |
1. Burning is fast oxidation process in which large amount of energy is produced. 2. Only air is necessary for burning. |
Objective Type Questions
1. Fill in the blanks :
(a) _____ is the most abundant inert gas present in air.
(b) Oxides of sulphur and nitrogen combine with rain water to form ______ and ______ which cause ______
(c) ______ and _____ are the most common air pollutants.
(d) ______ discovered the oxygen gas.
(e) Oxygen occupies about ______ of air by volume.
Answer
(a) Argon
(b) sulphuric acid, nitric acid , acid rain
(c) NO2, CO
(d) Joseph Priestly
(e) 21%
2. Match the following :
|
Column A |
Column B |
|
(a) Global warming |
(i) Hydrated ferric oxide |
|
(b) Acid rain |
(ii) Manganese dioxide |
|
(c) Rust |
(iii) Carbon dioxide |
|
(d) Catalyst |
(iv) Methane |
|
(e) Photosynthesis |
(v) Nitrogen dioxide |
Answer
|
Column A |
Column B |
|
(a) Global warming |
(iv) Methane |
|
(b) Acid rain |
(v) Nitrogen dioxide |
|
(c) Rust |
(i) Hydrated ferric oxide |
|
(d) Catalyst |
(ii) Manganese dioxide |
|
(e) Photosynthesis |
(iii) Carbon dioxide |
Multiple Choice Questions
1. A fuel when used releases least amount of pollutants in the air.
(a) sulphur dioxide
(b) chlorofluorocarbon
(c) smoke
(d) CNG
Answer
(d) CNG
2. The natural way of adding oxygen to air which involves green plants is called
(a) photosynthesis
(b) respiration
(c) burning
(d) dissolution
Answer
(a) photosynthesis
3. Which one of the following is most likely to be corroded?
(a) a stainless steel cup-board
(b) a galvanised iron bucket
(c) an iron hammer
(d) a tin plated iron box
Answer
(c) an iron hammer
4. The process by which oxidation of food in our body takes place is
(a) photosynthesis
(b) respiration
(c) decomposition
(d) combustion
Answer
(b) respiration
Additional Questions
A. Air : A Mixture of Gases
1. What was the ancient belief regarding the nature of matter ?
Answer
The ancient belief about the nature of matter was that it is compound of four elements:
a. fire
b. air
c. wood
d. earth
2. Name the main components of air.
Answer
The main components of air are:
a. nitrogen
b. oxygen
c. carbon dioxide
d. water vapour
e. inert or noble gases
3. Mention the contribution of the following scientists :
a. Antoine Lavoisier
b. Robert Boyle
c. Joseph Priestley
d. Sir W. Ramsay
Answer
a. Antoine Lavoisier: Conducted experiments to know the nature of combustion.
b. Robert Boyle: Discovered a rule about how gases behave
c. Joseph Priestley: Prepared oxygen by heating red mercuric oxide with infra red rays from Sun and proved that air was not an element.
d. Sir W. Ramsay: Sir William Ramsay, along with Lord Raleigh discovered argon; a noble gas, which is also called as rare gas or inert gas. He also prepared neon, krypton and xenon by distillation of liquid air. In 1910, he discovered radon.
4. State three uses of water vapour in the air.
Answer
- Provides moisture for plant and animal growth.
- Determines climatic conditions by providing rain, snow, mist etc.
- Prevents undue drying up of the plant and animal bodies.
5. State one method by which :
a. Oxygen is added to air
b. Carbon dioxide is added to air
c. Oxygen is removed from the air
d. Carbon dioxide is removed from the air
Answer
a. Photosynthesis by green plants
b. Combustion of various compounds
c. Respiration by living organisms
d. Plants- during photosynthesis.
6. Describe a simple experiment to show that l/5th of air is oxygen.
Answer
Aim: To show that l/5th of the air is oxygen.
Apparatus required: Glass trough, bell jar, stopper, water, phosphorus, evaporating dish
Procedure:
- A glass trough is filled with water
- A dry evaporating dish containing white phosphorus is made to float on the water.
- This apparatus is covered with a well stoppered bell jar with markings on its side.
- A glowing iron wire is introduced into the bell jar by opening the stopper
- The phosphorus is carefully ignited.
- Re-stopper the apparatus
- The phosphorus bums with a brilliant flame farming dense white fumes of phosphorus pentoxide.
- Soon the burning ceases and the water level starts rising.
- The water occupies approximately l/5th of the original volume, as the fumes dissolve in water.
- Some phosphorus is left unburnt in the dish. The air left behind in the bell jar does not allow the phosphorus to burn.
Inference:
The experiment shows that the volume of air occupied by oxygen is 1/5th.
7. Give reasons to support the fact that air is a mixture.
Answer
Air is a mixture can be supported by the following evidences.
a. Variable composition at different places
b. Lacks distinct properties of its own
c. Has no definite boiling point
d. Components of air cannot be easily separated by physical means.
e. Formation of air does not involve any energy change.
f. Cannot be represented by a chemical formula.
8. Name the products formed when a candle burns in air.
Answer
Carbondioxide and water vapour are formed due to the burning of candle.
Objective Type Questions
A. Fill in the blank spaces by choosing the correct words from the given list.
List: oxygen, carbonic, sulphur dioxide gas, precipitation, helium
a. _______ can cause acid rain.
b. Every nine parts of water by weight contains eight parts by weight of _______.
c. Dust particles help in the _______ of water vapour in air.
d. _______ gas is used for filling weather observation balloons.
e. Solution of carbon dioxide in water is called _______ acid.
Answer
a. Sulphur dioxide gas can cause acid rain.
b. Every nine parts of water by weight contains eight parts by weight of oxygen.
c. Dust particles help in the precipitation of water vapour in air.
d. Helium gas is used for filling weather observation balloons.
e. Solution of carbon dioxide in water is called carbonic acid.
B. Statements given below are incorrect. Write the correct statements :
1. Carbon dioxide gas allows the earth to radiate out heat rapidly.
Answer
Carbon dioxide gas does not allow the earth to radiate out heat rapidly.
2. Helium gas at low pressure is used for filling electric bulbs.
Answer
Argon gas at low pressure is used for filling electric bulbs.
3. Symbiotic bacteria are present in nodules of cereal plants such as wheat.
Answer
Symbiotic bacteria are present in nodules of pod bearing plants such as peas, grams, etc.
4. During thunder and lightning, nitrogen and oxygen combine to form nitrogen
dioxide gas.
Answer
During thunder and lightning, nitrogen and oxygen combine to form nitric oxide gas.
5. The percentage of oxygen in air by volume, varies from 21% to 22%.
Answer
The percentage of oxygen in air by volume, varies from 20.8% to 20.9%.
C. Match the statements in Column A, with those in Column B.
|
Column A |
Column B |
|
1. Largest constituent of air, which dilutes the activity of oxygen. |
(a) Oxygen |
|
2. A gas used for filling weather observation balloons. |
(b) Carbonic acid |
|
3. An acid formed by the dissolution of sulphur dioxide gas in water. |
(c) Sulphuric acid |
|
4. An acid formed by the dissolution of carbon dioxide in water. |
(d) Helium |
|
5. A gas vital for respiration. |
(e) Nitrogen |
Answer
|
Column A |
Column B |
|
1. Largest constituent of air, which dilutes the activity of oxygen. |
(e) Nitrogen |
|
2. A gas used for filling weather observation balloons. |
(d) Helium |
|
3. An acid formed by the dissolution of sulphur dioxide gas in water. |
(c) Sulphuric acid |
|
4. An acid formed by the dissolution of carbon dioxide in water. |
(b) Carbonic acid |
|
5. A gas vital for respiration. |
(a) Oxygen |
D. Write ‘True’ or ‘False’ in front of following statements.
1. Atmospheric nitrogen is directly absorbed by the plants to form plant proteins.
Answer
False.
Atmospheric nitrogen cannot be directly absorbed by the plants to form plant proteins.
2. Water containing dissolved carbon dioxide can dissolve marble.
Answer
True.
3. Nitrogen is a gaseous non-metal essential for respiration.
Answer
False.
Oxygen is a gaseous non-metal essential for respiration.
4. The area where a lot of fuel burns has more percentage of carbon dioxide.
Answer
True.
5. The trapping of solar heat energy in the earth’s atmosphere is called greenhouse effect.
Answer
True.
E. Tick (√) the most appropriate answer.
1. A gas which dilutes the activity of oxygen in air is :
(a) carbon dioxide
(b) sulphur dioxide
(c) nitrogen
(d) noble gases
Answer
(c) nitrogen
2. Symbiotic bacteria is not present in the nodules of :
(a) gram plant
(b) rice plant
(c) sweet peas plant
(d) peas plant
Answer
(b) rice plant
3. The presence of water vapour in air is essential for :
(a) health and comfort of animals
(b) rate of evaporation from plants and animals
(c) growth of plants
(d) all the above
Answer
(d) all the above
4. Which is not a polluting gas for the air?
(a) Sulphur dioxide gas
(b) Nitrogen dioxide gas
(c) Carbon monoxide gas
(d) Neon gas
Answer
(d) neon gas
5. The humans pollute the air by :
(a) burning a vast amount of coal
(b) burning waste materials
(c) using petrol and diesel vehicles
(d) all the above
Answer
(d) all the above
Study Questions
1. Briefly state the importance of following constituents of air :
(a) Oxygen,
(b) Nitrogen,
(c) Carbon dioxide,
(d) Water vapour.
Answer
(a) Oxygen in the air is essential for respiration and burning.
(b) Nitrogen dilutes the activity of oxygen in air. Its compounds are very useful for the growth of plants.
(c) Carbon-dioxide acts as a food for plants and in the regeneration of oxygen. It also helps in trapping heat radiations on earth.
(d) Water vapour controls climatic conditions and is very essential for the health and comfort of all living beings.
2. (a) What do you understand by the term polluted air?
(b) State and explain two ways by which air gets polluted in nature.
Answer
(a) When the air contains harmful or undesirable substances, generated by the activities of man or nature, such that their concentration interferes with human health or is injurious to plants or animals, it is said to be polluted air.
(b) Air gets polluted in nature by following ways :
- 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.
3. (a) Name and briefly explain four ways by which pollution of air is caused by humans.
(b) Name and briefly explain four ways by which pollution of air caused by humans is minimised.
Answer
(a) Pollution of air is caused by humans in the following ways :
- Large amount of coal burnt in thermal plants throw out huge amounts of smoke and ash in the atmosphere.
- Vehicles using petrol or diesel give out a lot of smoke and harmful gases like carbon-dioxide, lead, carbon- monoxide.
- Burning of garbage causes a lot of pollution due to the formation of carbon-monoxide, sulphur dioxide and nitrogen dioxide.
- Pesticides spread in the fields also cause air pollution.
(b) Pollution of air by humans can be minimised in the following manner :
- In the thermal power plants, steel plants etc., electric precipitators should be used to reduce the smoke and ash entering the air.
- Efficient internal combustion engines should be used in vehicles.
- Improved chulha or stoves should be used to minimise the production of smoke and carbon-monoxide.
- We must grow more trees as they absorb harmful gases.
4. (a) What is greenhouse effect?
(b) How is greenhouse effect produced?
Answer
(a) The trapping of solar heat energy in earth’s atmosphere is called greenhouse effect.
(b) The solar heat radiations consist of very short wavelength infrared radiations. These radiations can easily pass through the atmosphere. These radiations are absorbed by the Earth’s surface and temperature of the Earth rises during the daytime. At night, the Earth radiates out heat radiations of very long wavelength which cannot easily penetrate through the atmosphere because carbon-dioxide and clouds act as excellent reflectors.
Thus, heat radiations are trapped in the atmosphere which keep the Earth warm during night. This trapping of outgoing solar heat energy in Earth’s atmosphere is greenhouse effect.
5. Discuss harmful effects of greenhouse effect.
Answer
Large amount of carbon-dioxide in the polluted air results in increase of greenhouse effect which has raised the average temperature of the Earth by 2°C. This results in global warming which, in turn, will melt ice on the polar caps, thereby raising the level of sea water by a few metres. This can result in submerging of coastal areas and islands causing excessive damage.
6. Discuss two useful applications of greenhouse effect.
Answer
Two useful applications of greenhouse effect are:
- Growing vegetables and flowers in snow-bound regions: Sheds using glass walls are built which allow smaller wavelength of solar heat radiations to pass into the shed but does not allow the longer wavelength of heat radiations to pass out during night. This keeps the shed reasonably warm for flowers and vegetables to grow.
- Use of glass in keeping homes warm: In cold countries, the glass windows and doors allow the smaller wavelength of heat radiations of solar energy to pass into the rooms but does not allow longer wavelength of heat radiations to pass out. Thus, greenhouse effect takes place and rooms keep reasonably warm.
7. What is the significance of water vapour in air?
Answer
Significance of water vapour in atmosphere is as follows:
- 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.
- The presence of water vapour controls the rate of evaporation from the plants and animals.
- The presence of water vapour is very essential for the growth of plants.
- It is very essential for the health and comfort of animals.
8. Name three noble gases present in the air. State their one industrial use^
Answer
Three noble gases present in the air are :
- Helium: It is used for filling weather observation balloons.
- Argon: It is used for filling electric bulbs at low pressure.
- Neon: It is used for making advertising glow tubes, used on big shops, hotels etc. at night.
9. What problems are caused by the presence of following in excessive amount in the air?
(a) dust particles
(b) smoke particles
(c) sulphur dioxide gas
(d) nitrogen dioxide gas
(e) carbon monoxide gas
(f) hydrorgen sulphide
Answer
(a) Excess of dust particles can cause serious respiratory problems.
(b) Excess of smoke particles in air can cause serious respiratory problems.
(c) Excess of sulphur dioxide gas can lead to acid rain and cause respiratoiy problems.
(d) Excess of nitrogen dioxide gas can lead to acid rain damaging plants and properties. They also cause respiratory problems. They lead to thinning of ozone layer too.
(e) Excess of carbon monoxide leads to breathing problem and can be fatal.
(f) Excess of hydrogen sulphide can lead to serious respiratory problems as it is very toxic. It can also affect the nervous system in humans.
B. Oxygen
1. Fill in the blanks:
a. ______ discovered the oxygen gas.
b. Oxygen is slightly ______ than air.
c. Manganese dioxide acts as a ______
d. Oxygen is collected by the ______ displacement of ______
e. Oxygen occupies about ______ of air by volume.
f. Oxygen is ______ to litmus testing.
Answer
a. Joseph Priestley
b. heavier
c. catalyst
d. downward , water
e. 1/5 th
f. neutral
2. (i) What happens when (a) mercuric oxide and (b) potassium nitrate are heated ?
Answer
ii. Why is potassium chlorate is not used for laboratory preparation of oxygen ?
Answer
Potassium chlorate is a white solid. When it is heated strongly, first it melts and then it begins to boil, giving of oxygen. Potassium chlorate needs strong heating. That is why it is not used for laboratory preparation of oxygen.
3. What happens when the following substances burn in oxygen ? Also give the
balanced chemical equations for each of the reactions.
a. Sulphur
b. Carbon
c. Phosphorus
d. Sodium
e. Magnesium
f. Iron
Answer
(a) Sulphur bums with a bright bluish flame, giving the pungent smell of sulphur dioxide.
(b) Carbon bums with bright sparks, forming carbon dioxide
- Do not collect the first-few bubbles of the gas produced as it is the air in the delivery tube which is driven out
- Method of collection of gas should be appropriate.
- Keep all inflammable and burning apparatus away as oxygen is a supporter of combustion.
- Formed when non metals are burnt in oxygen
- When dissolved in water form acids, eg. carbon dioxide [CO2]
- Formed when metals are burnt in air
- Turn red litmus to blue. eg. potassium oxide [K2O]
Objective Type Questions
|
Column A |
Column B |
|
1. A mixture of oxygen and carbon dioxide used for artificial respiration. |
(a) Manganese dioxide |
|
2. A compound which on strong heating yields oxygen gas. |
(b) Sodium |
|
3. The process of coating zinc on the surface of iron to prevent rusting. |
(c) Carbogen |
|
4. A catalyst used in laboratory preparation of oxygen from hydrogen peroxide. |
(d) Potassium nitrate |
|
5. A metal which burns with a golden yellow flame in oxygen. |
(e) Galvanising |
Answer
|
Column A |
Column B |
|
1. A mixture of oxygen and carbon dioxide used for artificial respiration. |
(c) Carbogen |
|
2. A compound which on strong heating yields oxygen gas. |
(d) Potassium nitrate |
|
3. The process of coating zinc on the surface of iron to prevent rusting. |
(e) Galvanising |
|
4. A catalyst used in laboratory preparation of oxygen from hydrogen peroxide. |
(a) Manganese dioxide |
|
5. A metal which burns with a golden yellow flame in oxygen. |
(b) Sodium |
Study Questions
- The white crystals of potassium nitrate slowly melt to form a colourless liquid.
- The glowing splint bursts into flame, showing that molten potassium nitrate gives off oxygen gas.
- The oxygen gas is evolved at room temperature. No heating is required.
- The rate of evolution of oxygen is fairly fast.
- Hydrogen peroxide or manganese dioxide are not dangerous chemicals and hence, can be handled easily.
- Oxygen is a colourless, odourless and tastless gas.
- Under laboratory conditions, oxygen is practically insoluble in water.
- Oxygen is slightly heavier than air.
- Under high pressure and low temperature, oxygen can be changed to liquid state. Liquid oxygen is slightly bluish in colour.
- Spaceships : Liquid oxygen is used for burning fuel in rockets and spaceships as there is no air in the space.
- Cutting and welding : Oxygen and hydrogen are made to bum in a specially designed torch. The oxy- hydrogen flame can easily melt metals and used for cutting and welding them.
- Chemical industry : Oxygen is used in large amount for preparing sulphuric acid from sulphur and nitric acid from ammonia.
- 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.
- Galvanising: iron metal is coated with zinc.
- Enamelling: iron surface is baked with mixutre of silicates at high temperature.
- Coating with red lead oxide paint or tar on iron surface.
- Oils and grease coating on iron surface cuts off moist air and prevents rusting.