Hydrogen

Which of the following metals does not react with water or acid to produce hydrogen gas?

1. Magnesium
2. Iron
3. Copper
4. Zinc

Answer

Copper

Reason — Copper (Cu) is less reactive and lies below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute acids and therefore does not produce hydrogen gas. Also, copper does not react with water (cold or hot) to give hydrogen.

Which of the following compounds is formed along with hydrogen gas when magnesium reacts with steam ?

1. Mg(OH)₂
2. MgO
3. MgH₂
4. MgCl₂

Answer

MgO

Reason — When magnesium reacts with steam (water vapour), it forms magnesium oxide (MgO) along with hydrogen gas (H₂).

Mg(s) + H₂​O(g) → MgO(s) + H₂​(g)

The gas produced at anode when electrolysis of water is done is :

1. H₂
2. O₂
3. SO₂
4. None

Answer

O₂

Reason — During water electrolysis, hydrogen gas (H₂) is produced at the cathode (negative electrode), and oxygen gas (O₂) is produced at the anode (positive electrode).

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 the presence of diffused sunlight, the hydrogen and chlorine molecules undergo a combination reaction to form hydrogen chloride.

H₂​(g) + Cl₂​(g) $\xrightarrow{\text{sunlight}}$ 2HCl(g)

The metal which reacts with cold water to produce hydrogen is

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

Answer

calcium

Reason — Calcium (Ca) reacts readily with cold water to form calcium hydroxide (Ca(OH)₂) and hydrogen gas (H₂).

Ca(s) + 2H₂​O(l) → Ca(OH)₂​(aq) + H₂​(g)

In metal reactivity series, the more reactive metals are at

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

Answer

top

Reason — The reactivity series is a list of metals arranged in order of their ability to displace other metals from solutions or react with substances like water and acids. The most reactive metals, such as potassium and sodium, are at the top, while less reactive metals like gold and platinum are at the bottom.

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 responsible for producing heat and light, hydrogenated oil for using as a fuel, for the manufacture of fertilizers, etc.

Hydrogen is

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

Answer

combustible

Reason — Hydrogen is combustible in nature, but is itself a non-supporter of combustion.

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 (CO) and hydrogen (H₂).

Assertion (A): On the earth, hydrogen is mostly found in the form of compounds.

Reason (R): Hydrogen is a highly reactive element.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — Hydrogen readily reacts with other elements, especially oxygen, to form compounds like water, and with metals as well. This reactivity is one of the reasons it is mostly found in compounds.

Assertion (A): In the laboratory preparation of hydrogen, granulated zinc is reacted with dilute acid.

Reason (R): Granulated zinc contains copper as an impurity.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Explanation — In the laboratory, hydrogen is commonly prepared by reacting granulated zinc with a dilute acid (dil. HCl / dil. H₂SO₄). So, Assertion (A) is true.
Granulated zinc may contain small impurities such as copper, which can help the reaction start faster. So, Reason (R) is true.
However, Reason (R) is not the correct explanation of Assertion (A) as granulated zinc is mainly used because its rough, uneven surface provides larger effective surface area, so hydrogen is evolved at a steady and controllable rate.

Assertion (A): Pure hydrogen burns with a pop sound in air.

Reason (R): Hydrogen forms an explosive mixture with air.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is false but R is true.

Explanation — Pure hydrogen burns quietly (pale blue flame). The pop sound is heard only when hydrogen is mixed with air/oxygen. So, Assertion (A) is false.
Hydrogen forms an explosive mixture with air, which produces the pop on ignition. So, Reason (R) is true.

Assertion (A): Hydrogen is used for the extraction of less reactive metals like copper and lead.

Reason (R): Hydrogen is a good reducing agent.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — Hydrogen acts as a good reducing agent. When hydrogen gas is passed over hot metallic oxides of copper, lead, iron, etc., it removes oxygen from them and thus reduces them to their corresponding metals.

Assertion (A): Oxyhydrogen flame is used for cutting and welding metals.

Reason (R): For cutting and welding metals, a low temperature is required.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Explanation — Oxyhydrogen flame is used for cutting and welding metals. So, Assertion (A) is true.
For cutting and welding metals, a high temperature is required. Oxyhydrogen flame has a temperature of about 2800°C-3000°C, which is sufficient to melt the metals. So, Reason (R) is false.

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

Indicate which of the following statements are true and which are false and correct the false statements:

(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.

Match the statements in Column A with the words in Column B.

Answer

Name the following:

(a) The process in which oxygen is added or hydrogen is removed.

(b) A process by which hydrogen gas is manufactured.

(c) A solid conductor through which current enters or leaves the electrolyte.

(d) The charged particles present in an electrolyte.

(e) A substance which removes oxygen from a compound.

Answer

(a) Oxidation

(b) Bosch process

(c) Electrode

(d) Ions

(e) Reducing agent

Give examples :

(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) A metallic oxide which can be reduced into metal by hydrogen.

(d) An electrolyte.

(e) A metal of which an electrode is made.

Answer

(a) Sodium (Na) and Potassium (K)

(b) Iron (Fe)

(c) Copper(II) oxide (CuO)

(d) Copper(II) sulphate solution (CuSO₄)

(e) Copper

Complete and balance the following chemical 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 (steam) ⟶ Fe₃O₄ + 4H₂

(f) 2K + 2H₂O ⟶ 2KOH + H₂

Define:

(a) catalytic hydrogenation

(b) oxidation

(c) reduction

(d) redox reaction

(e) electrolysis

(f) electrolyte

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.

(e) Electrolysis is a process in which an electric current is passed through an aqueous solution or a molten state of a compound to bring about a chemical change.

(f) Electrolytes are the compounds that in aqueous or molten state that conduct electric current through them because they contain free and mobile ions.

How would you show that hydrogen gas is neutral in nature ?

Answer

Hydrogen gas is neutral to litmus, i.e. no change is observed in the colour of either moist blue or red litmus paper when it is introduced into a jar containing hydrogen. This proves that hydrogen gas is neutral in nature.

Give reasons for the following:

Hydrogen can be used as a fuel.

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.

Give reasons for the following:

Though hydrogen is lighter than air it cannot be collected by downward displacement of air.

Answer

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.

Give reasons for the following:

A pop sound is produced when hydrogen gas is burnt.

Answer

A pop sound is produced when hydrogen gas is burnt because of the presence of impurities in it.

Give reasons for the following:

Helium has replaced hydrogen in weather forecasting balloons.

Answer

Hydrogen gas is highly inflammable in nature, so it is replaced by helium for filling in weather forecasting balloons.

Give reasons for the following:

Nitric acid is not used for the preparation of hydrogen gas.

Answer

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.

The chemical equation given below represents a redox reaction.

PbO (Lead monoxide) + H₂ ⟶ Pb (Lead) + H₂O

(a) Name the reactant which gets :
(i) reduced
(ii) oxidised.

(b) Which of the reactants acts as an oxidising agent ?

Answer

(a)
(i) The reactant which gets reduced is PbO (Lead oxide).

(ii) The reactant which gets oxidised is H₂ (Hydrogen gas).

(b) PbO (Lead monoxide) acts as the oxidising agent.

(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

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

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.

Give three differences between Cathode and anode.

Answer

Give three differences between Cation and anion.

Answer

(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?

(e) Give one chemical test for hydrogen.

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.

(e) Hydrogen gas burns in air with a pop sound. This is because of the presence of impurities in it. This method is widely used as a test to identify hydrogen.

The diagram given below shows electrolysis of water. Answer the following questions :

(a) Label A, B, C, D, E and F.

(b) Why is acidulated water used ?

(c) What is the ratio by volume for the gases collected ?

Answer

(a)
A → Hydrogen (H₂)
B → Oxygen (O₂)
C → Electrolytic Cell
D → Acidulated Water (Electrolyte)
E → Cathode
F → Anode

(b) Acidulated water is used as pure water is a bad conductor of electricity. When a small amount of acid, alkali or salt is added to it, only then it conducts electricity.

(c) Ratio by volume of the gases collected
Hydrogen : Oxygen = 2 : 1