Fill in the blanks:
(a) Hydrogen is ............... than air.
(b) Hydrogen is ............... soluble in water.
(c) Hydrogen burns with a ............... flame and ............... sound is heard.
(d) A metal ............... hydrogen in the reactivity series gives hydrogen with ............... .
(e) Hydrogen reacts with metal oxides to form ............... and ............... .
(f) Oxidation is the removal of ............... or addition of ............... .
(g) In redox reactions, oxidation and reduction occurs ............... .
(c) pale blue, pop
(d) above, dilute acids
(e) metal, water
(f) hydrogen, oxygen
Indicate which of the following statements are true and which are false:
(a) Hydrogen molecule is monovalent.
(b) The removal of hydrogen from a substance is called reduction.
(c) Nitric acid cannot be used to prepare hydrogen by its action on active metals.
(d) The reaction between hydrogen and nitrogen to form ammonia is reversible.
(e) Zinc can liberate hydrogen from water, acid and alkali solution.
(f) Hydrogen is combustible as well as a supporter of combustion.
(g) Hydrogen gas is easily liquefiable.
Corrected statement — Hydrogen molecule is divalent.
Corrected statement — The removal of oxygen from a substance is called reduction.
Corrected statement — Hydrogen is combustible but it is non-supporter of combustion.
Corrected statement — Hydrogen gas cannot be easily liquefied.
Complete and balance the following equations:
(a) H2 + .................... ⟶ 2HCl
(b) H2 + S ⟶ ........................
(c) Zn + ................ ⟶ ZnCl2 + H2
(d) CuO + .............. ⟶ Cu + .............
(e) Fe + H2O ⟶ ................. + ...............
(f) K + H2O ⟶ .................. + ...............
(a) H2 + Cl2 ⟶ 2HCl
(b) H2 + S ⟶ H2S
(c) Zn + 2HCl ⟶ ZnCl2 + H2
(d) CuO + H2 ⟶ Cu + H2O
(e) 3Fe + 4H2O ⟶ Fe3O4 + 4H2
(f) 2K + 2H2O ⟶ 2KOH + H2
Give reasons for the following:
(a) Hydrogen can be used as a fuel.
(b) Though hydrogen is lighter than air it cannot be collected by downward displacement of air.
(c) A pop sound is produced when hydrogen gas is burnt.
(d) Helium has replaced hydrogen in weather observation balloons.
(e) Nitric acid is not used for the preparation of hydrogen gas.
(a) Hydrogen has high heat of combustion and is pollution free so it is used as a fuel. Liquid hydrogen is used as a rocket fuel.
(b) Though hydrogen is lighter than air it cannot be collected by downward displacement of air because a mixture of hydrogen and air can lead to an explosion so it is not safe to collect hydrogen gas by this method.
(c) A pop sound is produced when hydrogen gas is burnt because of the presence of impurities in it.
(d) Hydrogen gas is highly inflammable in nature, so it is replaced by helium for filling in weather forecasting balloons.
(e) Nitric acid is a strong oxidizing agent (even when it is dilute). It oxidises hydrogen gas converting it into water which defeats the purpose. Hence, nitric acid is not used for the preparation of hydrogen gas.
Name the following:
(a) Two metals which give hydrogen with cold water.
(b) A metal which liberates hydrogen only when steam is passed over red hot metal.
(c) The process in which oxygen is added or hydrogen is removed.
(d) A metallic oxide which can be reduced into metal by hydrogen.
(a) Potassium, sodium
(d) Lead monoxide (PbO)
(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?
(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.
How would you show that hydrogen:
(a) is a non-supporter of combustion?
(b) is lighter than air?
(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.
Hydrogen is a good reducing agent. What do you understand by the above statement? Explain with the help of copper oxide as an example.
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
(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?
(a) Bosch process
(b) Equations for the reactions of Bosch process are:
Production of water gas:
Reduction of steam by water gas:
(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 + H2O
Carbon monoxide is separated by passing through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.
CuCl + CO + 2H2O ⟶ CuCl.CO.2H2O
State four uses of hydrogen.
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.
(a) catalytic hydrogenation
(d) redox reaction
(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.
Equal volumes of hydrogen and chlorine are exposed to diffused sunlight to prepare
- hydrogen chloride
- sodium hydroxide
- hydrochloric acid
Reason — In diffused sunlight, hydrogen combines with equal volume of chlorine gas to form hydrogen chloride gas.
The metal which reacts with cold water to produce hydrogen is
Reason — Calcium, sodium and potassium are highly active metals which reacts with cold water to produce hydrogen gas.
In metal reactivity series, the more reactive metals are at
Reason — 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.
Hydrogen is responsible for producing
- heat and light
- hydrogenated oil
- all of the above
all of the above
Reason — 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.
- supporter of combustion
- neither supporter nor combustible
Reason — Hydrogen is combustible in nature, burns with a pale blue flame but is a non-supporter of combustion.
Water gas is a mixture of
- carbon monoxide and oxygen
- carbon monoxide and hydrogen
- hydrogen and oxygen
- hydrogen and nitrogen
carbon monoxide and hydrogen
Reason — Water gas is a mixture of carbon monoxide and hydrogen which is produced by passing steam over hot coke at 1000°C.
Match the statements in column A with those in column B.
|Column A||Column B|
|A metal which reacts with cold water to form hydrogen.||Reduction|
|A gas which is inflammable and a non-supporter of combustion.||Hydrogenation|
|A process in which vanaspati ghee is prepared from vegetable oils.||Oxidation|
|The removal of hydrogen or addition of oxygen.||Sodium|
|The addition of hydrogen or removal of oxygen.||Hydrogen|
|Column A||Column B|
|A metal which reacts with cold water to form hydrogen.||Sodium|
|A gas which is inflammable and a non-supporter of combustion.||Hydrogen|
|A process in which vanaspati ghee is prepared from vegetable oils.||Hydrogenation|
|The removal of hydrogen or addition of oxygen.||Oxidation|
|The addition of hydrogen or removal of oxygen.||Reduction|