Question 1

Question 6(a) Name the chemicals required to prepare hydrogen gas in the laboratory.(b) Give a balanced chemical equation for the reaction.(c) Draw a neat and well-labelled diagram for the laboratory preparation of hydrogen.(d) How is hydrogen gas collected? Why?

Accepted Answer

(a) Granulated zinc and dilute hydrochloric acid are the chemicals required to prepare hydrogen gas in the laboratory.(b) Zn + 2HCl ⟶ ZnCl2 + H2 (g)(c) Below diagram shows the laboratory preparation of Hydrogen gas:(d) Hydrogen gas is collected by downward displacement of water as it is sparingly soluble in water. Though hydrogen gas is lighter than air, it is not collected by downward displacement of air as a mixture of hydrogen and air can lead to an explosion.

Question 2

Question 7How would you show that hydrogen:(a) is a non-supporter of combustion?(b) is lighter than air?

Accepted Answer

(a) Hydrogen gas is a non-supporter of combustion is shown by the following experiment:Hold a hydrogen gas filled jar with its mouth downwards.Placed a lighted candle and cover it with this jar.The candle gets extinguished but the gas burns with a pop sound.This shows that hydrogen gas is non-supporter of combustion but itself is combustible.(b) Hydrogen gas is lighter than air is shown by the following experiment:Take a delivery tube and place one of its ends in a liquid soap solution kept in a trough and other end inside a flat bottom jar.In the flat bottom jar hydrogen gas is freshly prepared by the action of dilute hydrochloric acid on zinc granules.Hydrogen gas enters the soap solution through delivery tube.The soap bubbles containing hydrogen rise upward in the air.The rising soap bubbles prove that hydrogen is lighter than air.

Question 3

Question 8Hydrogen is a good reducing agent. What do you understand by the above statement? Explain with the help of copper oxide as an example.

Accepted Answer

When hydrogen is passed over hot metallic oxides of copper, lead, iron, etc. it removes oxygen from them and thus reduces them to their corresponding metals. Hence, hydrogen acts as a good reducing agent.When hydrogen gas is passed over heated copper oxide, copper oxide gets reduced to metallic copper by the removal of oxygen from it. The equation for the reaction is given below:CuO + H2 ⟶ Cu + H2O

Question 4

Question 9(a) Name a process by which hydrogen gas is manufactured.(b) Give equations for the reactions.(c) How is hydrogen separated from carbon dioxide and carbon monoxide?

Accepted Answer

(a) Bosch process(b) Equations for the reactions of Bosch process are:Production of water gas:Chot coke+H2Osteam→1000°C(CO+H2)water gas−Heat\underset{	ext{hot coke}}{	ext{C}} + \underset{	ext{steam}}{	ext{H}_2 	ext{O}} \xrightarrow {1000\degree	ext{C}} \underset{	ext{water gas}}{(	ext{CO} + 	ext{H}_2)} - 	ext{Heat}hot cokeC​+steamH2​O​1000°C​water gas(CO+H2​)​−HeatReduction of steam by water gas:(CO+H2)water gas+H2Osteam→450°CFe2O3/Cr2O3CO2+2H2+Heat\underset{	ext{water gas}}{(	ext{CO}+	ext{H}_2)} + \underset{	ext{steam}}{	ext{H}_2 	ext{O}} \xrightarrow [	ext{450\degree C}] {	ext{Fe}_2	ext{O}_3/ 	ext{Cr}_2	ext{O}_3} 	ext{CO}_2 + 2	ext{H}_2 + 	ext{Heat}water gas(CO+H2​)​+steamH2​O​Fe2​O3​/Cr2​O3​450°C​CO2​+2H2​+Heat(c) Hydrogen is separated from carbon dioxide by passing the mixture through water under pressure, where carbon dioxide gets dissolved leaving behind hydrogen. Carbon dioxide can also be separated by passing it through caustic potash (KOH) solution.2KOH + CO2 ⟶ K2CO3 + H2OCarbon monoxide is separated by passing through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.CuCl + CO + 2H2O ⟶ CuCl.CO.2H2O

Question 5

Question 10State four uses of hydrogen.

Accepted Answer

The four uses of hydrogen are:The oxy-hydrogen flame obtained by burning hydrogen and oxygen together has a very high temperature of about 2800°C - 3000°C. Hence it is used for cutting and welding of metals.It is used as a fuel as hydrogen has high heat of combustion.It is used for hydrogenation of vegetable oil.It is used as a reducing agent in extraction of metals.

Question 6

Question 11Define:(a) catalytic hydrogenation(b) oxidation(c) reduction(d) redox reaction

Accepted Answer

(a) Catalytic hydrogenation is a process by which hydrogen gas is passed through vegetable oils in the presence of a catalyst like Ni, Pt or Pd to convert the oils into vanaspati ghee.(b) Oxidation is a chemical process that involves addition of oxygen to a substance or removal of hydrogen from a substance.(c) Reduction is a chemical process that involves addition of hydrogen to a substance or removal of oxygen from a substance.(d) Redox reactions are those in which reduction and oxidation both take place simultaneously i.e., one substance is reduced while the other gets oxidized.

Question 7

Question 12(a)Equal volumes of hydrogen and chlorine are exposed to diffused sunlight to preparehydrogen chloridewatersodium hydroxidehydrochloric acid

Accepted Answer

hydrogen chlorideReason — In diffused sunlight, hydrogen combines with equal volume of chlorine gas to form hydrogen chloride gas.

Question 8

Question 12(b)The metal which reacts with cold water to produce hydrogen ismagnesiumaluminiumcalciumiron

Accepted Answer

calciumReason — Calcium, sodium and potassium are highly active metals which reacts with cold water to produce hydrogen gas.

Question 9

Question 12(c)In metal reactivity series, the more reactive metals are attopbottommiddlenone

Accepted Answer

topReason — The metals are arranged in decreasing order of their reactivity in metal activity series, so more reactive metals are placed at the top of the series.

Question 10

Question 12(d)Hydrogen is responsible for producingheat and lighthydrogenated oilfertilizersall of the above

Accepted Answer

all of the aboveReason — Hydrogen is used in preparation of vanaspati ghee from liquid vegetable fats by catalytic hydrogenation process. It is used to produce chemicals like ammonia which is used as a fertilizer. When burnt with oxygen, it produces oxy-hydrogen flame.

Question 11

Question 12(e)Hydrogen iscombustiblenon-combustiblesupporter of combustionneither supporter nor combustible

Accepted Answer

combustibleReason — Hydrogen is combustible in nature, burns with a pale blue flame but is a non-supporter of combustion.

Question 12

Question 12(f)Water gas is a mixture ofcarbon monoxide and oxygencarbon monoxide and hydrogenhydrogen and oxygenhydrogen and nitrogen

Accepted Answer

carbon monoxide and hydrogenReason — Water gas is a mixture of carbon monoxide and hydrogen which is produced by passing steam over hot coke at 1000°C.     C+H2O→1000°C(CO+H2)−Heat	ext{C}+ 	ext{H}_2 	ext{O} \xrightarrow {1000\degree 	ext{C}} 	ext({CO + H}_2) - 	ext{Heat}C+H2​O1000°C​(CO+H2​)−Heat

Question 13

Question 13Match the statements in column A with those in column B.Column AColumn BA metal which reacts with cold water to form hydrogen.ReductionA gas which is inflammable and a non-supporter of combustion.HydrogenationA process in which vanaspati ghee is prepared from vegetable oils.OxidationThe removal of hydrogen or addition of oxygen.SodiumThe addition of hydrogen or removal of oxygen.Hydrogen

Accepted Answer

Column AColumn BA metal which reacts with cold water to form hydrogen.SodiumA gas which is inflammable and a non-supporter of combustion.HydrogenA process in which vanaspati ghee is prepared from vegetable oils.HydrogenationThe removal of hydrogen or addition of oxygen.OxidationThe addition of hydrogen or removal of oxygen.Reduction

Question 14

Question 1Give balanced equations for the following conversions:Zinc to sodium zincate - using an alkali.Acidified water to hydrogen - by electrolysis.Water gas to hydrogen - industrially.Iron [III] oxide to iron - using hydrogen.Nitrogen to a basic gas - using hydrogen.

Accepted Answer

Zn + 2NaOH ⟶ Na2ZnO2 + H2 ↑2H2O ⇌ 2H2 + O2[CO+H2]water gas+H2Oexcess steam→Fe2O3450°CCO2+2H2+Δ\underset{	ext{water gas}}{[	ext{CO} + 	ext{H}_2 ]} + \underset{	ext{excess steam}}{	ext{H}_2	ext{O}} \xrightarrow[	ext{Fe}_2	ext{O}_3]{450 \degree 	ext{C}} 	ext{CO}_2 + 2	ext{H}_2 + \Deltawater gas[CO+H2​]​+excess steamH2​O​450°CFe2​O3​​CO2​+2H2​+ΔFe2O3 + 3H2 ⟶ 2Fe + 3H2ON2 + 3H2 ⇌ 2NH3

Question 15

Question 7Draw labeled diagrams for two experiments to prove that - hydrogen is lighter than air.

Accepted Answer

Experiment 1Procedure : Bubble hydrogen gas by means of a small pipe into a dish containing soap solution.Observation : Soap bubbles filled with H2 rise upwards.Conclusion : Hydrogen is lighter than air hence soap bubbles filled with hydrogen rise up.Experiment 2Procedure : Take two dry test tubes.Test tube 'A' - Filled with hydrogen.Test tube 'B' - Filled with air.Place test tube 'B' over test tube 'A' and test the gas in the upper test tube 'B' with a glowing splinter.Observation : A 'pop' sound is heard in test tube 'B'. [hydrogen burns with a 'pop' sound].Conclusion : Hydrogen is lighter than air and has moved upwards displacing the air.

Question 16

Question 8Starting from hydrogen gas how would you obtain(a) A neutral liquid(b) A basic gas(c) A metal by reduction of its heated oxide.[the metal formed is above iron in the activity series]

Accepted Answer

(a) Hydrogen burns quietly in oxygen with a pale blue flame and water is formed.2H2 + O2 ⟶ 2H2O(b) Three volumes of hydrogen, reacts with one volume of nitrogen to form ammonia which is a basic gas.N2+3H2⇌450-500 °CFe2NH3+Δ	ext{N}_2 + 3	ext{H}_2 \xrightleftharpoons[	ext{450-500 \degree C}]{	ext{Fe}} 	ext{2NH}_3 + \DeltaN2​+3H2​Fe450-500 °C​2NH3​+Δ(c) Hydrogen reduces oxides of less active metals e.g. zinc to form the reduced metal & water.ZnO + H2 ⟶ Zn + H2O

Question 17

Question 10State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.

Accepted Answer

As hydrogen is a strong reducing agent hence it reduces heated copper (II) oxide to copper. Therefore, the original black copper (II) oxide changes to reddish brown copper.CuO[black]+H2⟶Cu[reddish brown]+H2O\underset{	ext{[black]}}{	ext{CuO}} + 	ext{H}_2 \longrightarrow \underset{	ext{[reddish brown]}}{	ext{Cu}} + 	ext{H}_2	ext{O}[black]CuO​+H2​⟶[reddish brown]Cu​+H2​O

Question 18

Question 5In the industrial method of preparation of hydrogen by the Bosch process - give(a) Balanced equations for the first two main steps in the production of hydrogen(b) The reason for use of addition of a promoter to the catalyst in the final step.(c) The name of the solution which absorbs the unreacted carbon monoxide.

Accepted Answer

(a) Balanced equations for first two main steps of Bosch process:Step I — Production of water gasCcoke+H2Osteam→1000°C[CO+H2]water gas−Δ\underset{	ext{coke}}{	ext{C}} + \underset{	ext{steam}}{	ext{H}_2	ext{O}} \xrightarrow{1000 \degree 	ext{C}} \underset{	ext{water gas}}{[	ext{CO} + 	ext{H}_2 ]} - \DeltacokeC​+steamH2​O​1000°C​water gas[CO+H2​]​−ΔStep II — Reduction of steam to hydrogen by carbon monoxide[CO+H2]water gas+H2Oexcess steam→Fe2O3450°CCO2+2H2+Δ\underset{	ext{water gas}}{[	ext{CO} + 	ext{H}_2 ]} + \underset{	ext{excess steam}}{	ext{H}_2	ext{O}} \xrightarrow[	ext{Fe}_2	ext{O}_3]{450 \degree 	ext{C}} 	ext{CO}_2 + 2	ext{H}_2 + \Deltawater gas[CO+H2​]​+excess steamH2​O​450°CFe2​O3​​CO2​+2H2​+Δ(b) Promoter increases the efficiency of the catalyst.(c) Ammoniacal cuprous chloride solution [CuCl].

Hydrogen

Exercise

Objective Type Questions

Physical properties

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