Hydrogen

Exercise

Question 1

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 ............... .

Answer

(a) lighter

(b) sparingly

(c) pale blue, pop

(d) above, dilute acids

(e) metal, water

(f) hydrogen, oxygen

(g) simultaneously

Question 2

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.

Answer

(a) False
Corrected statement — Hydrogen molecule is divalent.

(b) False
Corrected statement — The removal of oxygen from a substance is called reduction.

(c) True

(d) True

(e) True

(f) False
Corrected statement — Hydrogen is combustible but it is non-supporter of combustion.

(g) False
Corrected statement — Hydrogen gas cannot be easily liquefied.

Question 3

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 ⟶ .................. + ...............

Answer

(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

Question 4

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.

Answer

(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.

Question 5

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.

Answer

(a) Potassium, sodium

(b) Iron

(c) Oxidation

(d) Lead monoxide (PbO)

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?

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 7

How would you show that hydrogen:

(a) is a non-supporter of combustion?

(b) is lighter than air?

Answer

(a) Hydrogen gas is a non-supporter of combustion is shown by the following experiment:

1. Hold a hydrogen gas filled jar with its mouth downwards.
2. Placed a lighted candle and cover it with this jar.
3. 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:

1. 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.
2. In the flat bottom jar hydrogen gas is freshly prepared by the action of dilute hydrochloric acid on zinc granules.
3. Hydrogen gas enters the soap solution through delivery tube.
4. The soap bubbles containing hydrogen rise upward in the air.

The rising soap bubbles prove that hydrogen is lighter than air.

Question 8

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

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 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?

Answer

(a) Bosch process

(b) Equations for the reactions of Bosch process are:

Production of water gas:

$\underset{\text{hot coke}}{\text{C}} + \underset{\text{steam}}{\text{H}_2 \text{O}} \xrightarrow {1000\degree\text{C}} \underset{\text{water gas}}{(\text{CO} + \text{H}_2)} - \text{Heat}$

Reduction of steam by water gas:

$\underset{\text{water gas}}{(\text{CO}+\text{H}_2)} + \underset{\text{steam}}{\text{H}_2 \text{O}} \xrightarrow [\text{450\degree C}] {\text{Fe}_2\text{O}_3/ \text{Cr}_2\text{O}_3} \text{CO}_2 + 2\text{H}_2 + \text{Heat}$

(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 + 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

Question 10

State four uses of hydrogen.

Answer

The four uses of hydrogen are:

1. 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.
2. It is used as a fuel as hydrogen has high heat of combustion.
3. It is used for hydrogenation of vegetable oil.
4. It is used as a reducing agent in extraction of metals.

Question 11

Define:

(a) catalytic hydrogenation

(b) oxidation

(c) reduction

(d) redox reaction

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 12(a)

Equal volumes of hydrogen and chlorine are exposed to diffused sunlight to prepare

1. hydrogen chloride
2. water
3. sodium hydroxide
4. hydrochloric acid

Answer

hydrogen chloride

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

Question 12(b)

The metal which reacts with cold water to produce hydrogen is

1. magnesium
2. aluminium
3. calcium
4. iron

Answer

calcium

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

Question 12(c)

In metal reactivity series, the more reactive metals are at

1. top
2. bottom
3. middle
4. none

Answer

top

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.

Question 12(d)

Hydrogen is responsible for producing

1. heat and light
2. hydrogenated oil
3. fertilizers
4. all of the above

Answer

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.

Question 12(e)

Hydrogen is

1. combustible
2. non-combustible
3. supporter of combustion
4. neither supporter nor combustible

Answer

combustible

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

Question 12(f)

Water gas is a mixture of

1. carbon monoxide and oxygen
2. carbon monoxide and hydrogen
3. hydrogen and oxygen
4. hydrogen and nitrogen

Answer

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.

     $\text{C}+ \text{H}_2 \text{O} \xrightarrow {1000\degree \text{C}} \text({CO + H}_2) - \text{Heat}$

Question 13

Match the statements in column A with those in column B.

Answer