Question 1

Question 3Explain Lavoisier's experiment which provided evidence to the discovery of components in air.

Accepted Answer

Apparatus: The apparatus was set up as shown, with the mercury in the curved necked retort and air in the bell jar.Procedure: The mercury in the retort was then heated for several days.Observation:A red layer was formed on the heated mercury surface in the retort.The level of mercury in the trough rose by 15\dfrac{1}{5}51​ .Conclusions:The oxygen in the retort combined with the mercury forming mercury [II] oxide [red layer] and the level in the trough rose by 15\dfrac{1}{5}51​ th of the original volume, thereby occupying the space of the used oxygen in the bell jar.The active part of the air removed by mercury on heating was named 'oxygen'.The remaining inactive part of the air in the bell jar was then named 'nitrogen'.

Question 2

Question 4Tabulate the various components of air, including the components with variable composition.

Accepted Answer

Component of AirCompositionNitrogen [N2]78-79%Oxygen [O2]21%Carbon dioxide [CO2]0.02-0.03%Rare gases[Argon, neon, krypton, helium, xenon, radon ]less than 1%Water vapourvariableDust particlesvariablePollutants[Carbon monoxide, sulphur dioxide, oxides of nitrogen,hydrogen sulphide]variable

Question 3

Question 6Of the total volume of air 4⁄5th is nitrogen. State the utility or consequence of this ratio.

Accepted Answer

The fact that 4⁄5th of the total volume of air is nitrogen is useful for the following reasons:Controlled Combustion — Nitrogen being a non-supporter of combustion, dilutes the activity of oxygen in air and controls the combustion of substances.Growth of Plants — Free nitrogen of air is converted into soluble nitrogen compounds which are absorbed by plants and contribute to their growth and development.Breathable Air — Nitrogen in the atmosphere dilutes the oxygen, making it safe for us to breathe. Without this dilution, pure oxygen could be harmful and even flammable.

Question 4

Question 7State how nitrogen is utilized by plants for their growth. Give a reason why nitrogen is used in flushing food packages.

Accepted Answer

Growth and development of plants — Free nitrogen of air is converted to soluble nitrogenous compounds in the soil. These are absorbed by plants and converted to plant proteins which play a vital role in their growth and development.Flushing food packages — Nitrogen being inert or unreactive is filled into food packets to drive out the oxygen. Hence, bacterial growth inside the food packages is reduced and thereby the food is well preserved and fresh.

Question 5

Question 8Oxygen of the air is utilized for 'combustion' and for 'respiration'. Compare the two with a suitable example.

Accepted Answer

Oxygen for combustionOxygen for respirationFuel [hydrocarbon]Food substances [glucose]Oxygen is neededOxygen is neededCarbon dioxide is releasedCarbon dioxide is releasedWater vapour is formedWater vapour is formedHeat and light may be evolvedHeat is evolvedRapid process at high temperatureSlow process at body temperatureCxHy + zO2 ⟶ xCO2 + y/2H2O + EnergyC6H12O6 + 6O2 ⟶ 6CO2 + 6H2O + EnergyExample : Fuels with oxygen burns to produce heat and light energy.Example : Plants, animals and humans respire by taking in oxygen naturally.

Question 6

Question 9State the utility of carbon dioxide for manufacture of food by plants. State its role in warming the earth's environment and in excess resulting in global warming.

Accepted Answer

Plants manufacture food by the process of photosynthesis. Carbon dioxide in the atmosphere is absorbed by the plants in the presence of chlorophyll [the green pigment in plants] and sunlight, resulting in the formation of carbohydrates and release of oxygen.The sun's rays consist of infrared, visible rays and ultra violet rays. Carbon dioxide in the atmosphere allows the reflected ultraviolet rays to pass through but prevents the infrared radiations from being radiated out, resulting in warming of the earth.Due to pollution, concentration of carbon dioxide in the atmosphere is increasing. This excess carbon dioxide is warming the earth's surface to a harmful extent resulting in global warming.

Question 7

Question 10State the utility of -(a) water vapour(b) rare or inert gases present in air.

Accepted Answer

(a) Utility of water vapour:For controlling evaporation.For determining climatic condition.For growth of plant and animal.(b) Utility of rare or inert gases:In advertisement signsIn observation balloonsIn electric lamps.In photography

Question 8

Question 11Give the environment effect of three polluting gases with a reason why nitrogen is not considered a polluting gas.

Accepted Answer

Environment effect of three different polluting gases:Sulphur dioxide — cause respiratory problemsNitrogen dioxide — initiates acid rainfallDust & smoke particles — causes respiratory problems and precipitates rain.Nitrogen is not considered a polluting gas for the following reasons:It is an inert or unreactive gas.It is utilized by plants for their growth and development.It controls combustion by diluting the activity of oxygen.It is not a greenhouse gas and does not contribute to global warming.

Question 9

Question 12Describe simple experiments to show the presence of –(a) oxygen and nitrogen component in air using a bell jar.(b) carbon dioxide in air using a test tube with outlets containing lime water.(c) water vapour in air using a glass tumbler and ice.

Accepted Answer

(a) To study the presence of oxygen and nitrogen componentApparatus : A trough , bell jar, cork and crucible, a piece of phosphorus.Procedure :The trough is filled with water and a bell jar divided into 5 equal parts, '1 to 5' is placed over it.A crucible containing white phosphorus is placed on a cork which is made to float on water.The level of water inside and outside are adjusted to one level.The phosphorus is then ignited by means of a heated wire.Observations :White fumes are seen initially in the bell jar and level of water in the bell jar rises by 1⁄5.Phosphorus + Oxygen ⟶ Phosphorus pentoxideConclusion :Oxygen the active component of air [i.e., 1⁄5th of air] is used up in burning.Nitrogen the inactive component of air [i.e., 4⁄5th of air] is not used up in burning.Hence air contains oxygen which supports combustion and nitrogen which does not support combustion.(b) To study the presence of carbon dioxide in airApparatus : A test tube containing lime water with two outlets - A and B.Procedure : Air is sucked slowly from the outlet BObservations : The lime water in the test tube turns milky.Conclusion : Air contains carbon dioxide which turns lime water milky.(c) To study the presence of water vapor in airProcedure : A glass tumbler filled with ice cubes is exposed to the air.Observations : Water droplets are seen on the outer surface of glass tumblerConclusion : Air contains water vapour which condenses on the cool outer surface.

Question 10

Question 13State four different properties of a compound and a mixture. With reference to the stated properties give reasons why air is considered a mixture and not a compound.

Accepted Answer

Four Properties of compounds:It has a fixed composition.It has definite set of properties.It cannot be separated by physical means.Chemical Formula possible.Four Properties of mixture:It has a variable composition.It has no definite properties.It cannot be separated by physical means.No chemical formula possible.Air is considered a mixture and not a compound because:Composition — Air has a variable compositionProperties — Air has no specific set of propertiesSeparation of components — Air can be separated into its components by physical meansChemical formula — No chemical formula is possible for air.

Question 11

Question 14Explain the term 'air pollution', with reference to air quality. State the sources of a few main pollutants.

Accepted Answer

Air pollution is the condition of air made unclean due to the introduction of foreign elements from natural sources and manmade sources to the air.Sources of a few main pollutants are:Natural Sources:Volcanic eruptionsLightning dischargeMan-made Sources:Automobile exhaustsChemical industriesBurning of fuels

Question 12

Question 15Identify the acidic oxides responsible for acid rain. State how their presence results in formation of acid rain. Give a reason why acid rain damages heritage buildings.

Accepted Answer

Acidic oxides responsible for acid rain are:Oxides of Sulphur — Sulphur dioxide [SO2]Oxides of Nitrogen — Nitrogen dioxide [NO2]Formation of acid rain:The acidic oxides of Sulphur and Nitrogen combine with water vapour in presence of sunlight forming the respective acids.Sulphur dioxide + water vapour ⟶ Sulphurous acid [H2SO3]Sulphur trioxide + water vapour ⟶ Sulphuric acid [H2SO4]Nitric oxide + oxygen ⟶ nitrogen dioxide [NO2 ]Nitrogen dioxide + water ⟶ Nitrous acid [HNO2] & Nitric acid [HNO3]Presence of these acids causes acid rain.Damage to heritage buildings:Acid rain damages heritage buildings as it corrodes metallic surfaces & weakens building materials such as statues, marble, limestone [CaCO3] etc. It causes damage to heritage structures such as the Taj Mahal, which is made of limestone and reacts with acids present in acid rain.

Question 13

Question 16In the laboratory preparation of oxygen from hydrogen peroxide – answer the following:(a) Draw a neat and labelled diagram for the method used in above preparation.(b) Name the catalyst used in the preparation and state its function.(c) State the word equation for the reaction involving the above preparation of oxygen.(d) State the method of collection of the oxygen gas giving reasons.

Accepted Answer

(a) Labelled diagram of the laboratory preparation of oxygen from hydrogen peroxide is shown below:(b) Manganese dioxide is used as the catalyst. It alters the rate of the reaction and increases the rate of evolution of oxygen.(c) Hydrogen peroxide ⟶ Water + oxygen(d) Oxygen gas is collected by the downward displacement of water because:Oxygen is very slightly soluble in waterOxygen is almost as heavy as air hence it cannot be collected over air.

Question 14

Question 17Give word equations for the reactions of –(a) Non-metals —SulphurCarbonPhosphorus(b) Metals —SodiumCalciumMagnesiumwith oxygen.

Accepted Answer

(a) Non-MetalsSulphur + Oxygen ⟶ Sulphur dioxideCarbon + Oxygen ⟶ Carbon dioxidePhosphorus + Oxygen ⟶ Phosphorus pentoxide(b) MetalsSodium + Oxygen ⟶ Sodium oxideCalcium + Oxygen ⟶ Calcium oxideMagnesium + Oxygen ⟶ Magnesium oxide

Question 15

Question 18Distinguish between –(a) Combustion and respiration(b) Combustion & rustingwith suitable word equations only.

Accepted Answer

(a) Combustion and respirationCombustionRespirationHydrocarbon (candle) + Oxygen ⟶ Carbon dioxide + Water vapour + Energy (heat and light)Food + Oxygen ⟶ Carbon dioxide + Water vapour + Energy(b) Combustion & rustingCombustionRustingHydrocarbon (candle) + Oxygen ⟶ Carbon dioxide + Water vapour + Energy (heat and light)Iron + Oxygen →Moisture\xrightarrow{	ext{Moisture}}Moisture​ Hydrated Iron (III) Oxide (Rust) + Heat

Question 16

Question 19Give the main experimental points only to demonstrate that —(a) magnesium(b) candlegains weight on burning.

Accepted Answer

(a) Magnesium gains weight on burning due to the mass of the oxygen of the air which has combined with magnesium forming magnesium oxide.(b) Candle gains weight on burning due to mass of oxygen of the air which has combined with carbon and hydrogen of the candle CxHy producing water vapour and carbon dioxide.

Question 17

Question 20Give reasons for the following:(a) patients suffering from lung problems are kept in an oxygen tent.(b) oxygen finds utility in welding & cutting of metals.

Accepted Answer

(a) Oxygen tents provide artificial supply of extra oxygen to help patients with lung problems breathe easier. This reduces the load on the patient's lungs helping them to work better.(b) A mixture of oxygen with gases like hydrogen or acetylene on burning, produces high temperature flames of around 2800°C to 3000°C. Such high temperature flames are suitable for melting metals quickly. Hence, oxygen finds utility in welding & cutting of metals.

Question 18

Question 1Match the statements in List I with the correct answer from List II.List IList II1. The constituent of air which is around 0.02%A: Nitrogen2. The constituent of air which is inert or unreactiveB: Oxygen3. The constituent of air which is non-combustible, but supports combustionC: Sulphur dioxide4. A pollutant in air responsible for acid rainD: Carbon dioxide5. The main rare gas present in airE: Argon

Accepted Answer

List IList II1. The constituent of air which is around 0.02%D: Carbon dioxide2. The constituent of air which is inert or unreactiveA: Nitrogen3. The constituent of air which is non-combustible, but supports combustionB: Oxygen4. A pollutant in air responsible for acid rainC: Sulphur dioxide5. The main rare gas present in airE: Argon

Question 19

Question 2Give reasons for the following:Acid rain has caused damage to heritage structures such as the Taj Mahal.In the laboratory preparation of oxygen from potassium chlorate – manganese dioxide is added to the reactant.Oxygen gas does not affect moist blue litmus paper, but carbon dioxide turns it slightly pink.Oxidation of sulphur results in a product which turns moist blue litmus red.Combustion and respiration show similarity.

Accepted Answer

Acid rain damages heritage buildings because it corrodes metallic surfaces and weakens building materials like statues, marbles, limestone. Taj Mahal is predominantly made of lime stone and it reacts with acids present in acid rain.In the laboratory preparation of oxygen from potassium chlorate, manganese dioxide acts as a catalyst altering the rate of the reaction. It initiates the decomposition of potassium chlorate (KClO3) at a lower temperature.As oxygen is neutral in nature so it has no effect on blue litmus paper, but carbon dioxide is slightly acidic in nature, hence it turns blue litmus paper to slightly pink.The product obtained from the oxidation of sulphur is sulphur dioxide which is a non-metallic acidic oxide. Hence, it turns moist blue litmus red indicating its acidic nature.Combustion and respiration show similarity because they both involve the breakdown of substances with the use of oxygen to release energy, producing carbon dioxide and water as byproducts.

Question 20

Question 5Draw a neat labelled diagram for each of the following experiments.To determine the component of air used up in burning, by using phosphorus and a bell jar.To study the presence of carbon dioxide in air.To prove that oxygen is non-combustible, but supports combustion.To prepare oxygen in the laboratory from hydrogen peroxide and a catalyst.To demonstrate the burning of sulphur in a jar of oxygen.

Accepted Answer

To determine the component of air used up in burning, by using phosphorus and a bell jar.To study the presence of carbon dioxide.To prove that oxygen is non-combustible, but supports combustion.To prepare oxygen in the laboratory from hydrogen peroxide and a catalyst.To demonstrate the burning of sulphur in a jar of oxygen.

Air & Atmosphere

Air and atmosphere

Objective Type Questions