Living Science Chemistry Class 8 ICSE Solutions Chapter 7 Hydrogen

ICSE Living Science Chemistry for Class 8 Solutions Chapter 7 Hydrogen

Think And Answer (Page 88)

In the preparation of hydrogen in the laboratory, the end of the thistle funnel in the flask should be dipped in the acid. Why?
Answer:
In the preparation of hydrogen in the laboratory, the end of the thistle funnel in the flask should be dipped in the acid so that the gas may not escape from the thistle funnel.

Check Your Progress (Page 89)

Answer these questions.
Question 1.
Which is the most abundant element in the universe?
Answer:
Hydrogen.

Question 2.
Who named the gas hydrogen?
Answer:
Antoine Lavoisier, a French chemist, named the gas ‘hydrogen’.

Question 3.
What happens when steam is passed over magnesium?
Answer:
When steam is passed over heated magnesium, hydrogen gas is produced along with the corresponding magnesium oxide.

Question 4.
What is the electrode connected to the negative terminal called?
Answer:
Cathode.

Question 5.
Which metal is used to prepare hydrogen in the laboratory?
Answer:
Zinc.

Question 6.
What happens when a burning splinter is brought near the mouth of a gas jar containing hydrogen gas?
Answer:
Bring a burning splinter near the mouth of the gas jar. Being highly combustible, the gas bums with a pop sound and the splinter gets extinguished.

Question 7.
Which raw materials are used to produce hydrogen by Bosch’s process?
Answer:
Coke and steam.

A. Tick the most appropriate answer

Question 1.
Which of the following metals reacts with steam or acids to release hydrogen?
a. zinc
b. platinum
c. silver
d. gold
Answer:
a. zinc

Question 2.
Which of the following reacts explosively with dilute hydrochloric acid to liberate hydrogen?
a. aluminium
b. magnesium
c. zinc
d. potassium
Answer:
d. potassium

Question 3.
Which of the following is formed zinc reacts with steam? along with hydrogen when
a. ZnO₂
b. ZnO
c. Zn
d. none of these
Answer:
b. ZnO

Question 4.
What is the electrode connected to the positive terminal of an electrolytic cell called?
a. anode
b. electrolyte
c. cathode
d. none of these
Answer:
a. anode

Question 5.
In electrolysis of water, which gas is produced at the anode?
a. hydrogen
b. oxygen
c. carbon dioxide
d. nitrogen
Answer:
b. oxygen

Question 6.
Which of the following is water gas?
a. CO₂ + H₂O
b. CO + H₂O
c. CO₂ + H₂
d. CO + H₂O
Answer:

Question 7.
What is the chemical process that involves the addition of oxygen or the removal of hydrogen called?
a. reduction
b. oxidation
c. displacement
d. synthesis
Answer:
b. oxidation

B. Fill in the blanks.

Question 1.
Active metals react with cold water to liberate hydrogen gas and form the corresponding metal .
Answer:
Active metals react with cold water to liberate hydrogen gas and form the corresponding metal hydroxide.

Question 2.
Magnesium reacts with steam to form and hydrogen gas.
Answer:
Magnesium reacts with steam to form magnesium oxide and hydrogen gas.

Question 3.
An ceil is a device in which electrical energy is converted into chemical energy and vice versa.
Answer:
An electrolytic cell is a device in which electrical energy is converted into chemical energy and vice versa.

Question 4.
An electrode is a conductor used in an electrolytic cell and it conducts electricity into and out of an
Answer:
An electrode is a conductor used in an electrolytic cell and it conducts electricity into and out of an electrolyte.

Question 5.
Hydrogen combines with nitrogen to form in the presence of iron as a catalyst at a high pressure and temperature.
Answer:
Hydrogen combines with nitrogen to form ammonia in the presence of iron as a catalyst at a high pressure and temperature.

Question 6.
The flame is used for cutting and welding of metals.
Answer:
The oxy-hydrogen flame is used for cutting and welding of metals.

Question 7.
A reaction is a reaction in which both oxidation and reduction take place simultaneously.
Answer:
A redox reaction is a reaction in which both oxidation and reduction take place simultaneously.

C. Match the columns

1. Converting liquid vegetable oils into solid ghee	a. ammonia
2. Haber process	b. hydrogenation
3. Bosch’s process	c. addition of oxygen
4. Oxidation	d. water gas
5. The gas formed when hydrogen reacts with chlorine in diffused sunlight	e. electrolysis
6. Oxides of non-metals	f. hydrogen chlorid
	g. hydrocarbons

Answer:

1. Converting liquid vegetable oils into solid ghee	b. hydrogenation
2. Haber process	a. ammonia
3. Bosch’s process	d. water gas
4. Oxidation	c. addition of oxygen
5. The gas formed when hydrogen reacts with chlorine in diffused sunlight	f. hydrogen chloride
6. Producing hydrogen by passing electric current through water	e. electrolysis

D. Write true or false. Correct the false statements

Question 1.
Electrolytes conduct electricity in their aqueous solution or molten state to undergo decomposition into ions.
Answer:
True

Question 2.
Steam is passed over hot coke at 1000 °C in a converter to produce hydrogen gas.
Answer:
False; Steam is passed over hot coke at 1000°C in a converter to produce water gas.

Question 3.
Hydrogen changes the colour of litmus.
Answer:
False; Hydrogen does not change the colour of litmus.

Question 4.
The only product of combustion of hydrogen in air is water.
Answer:
True

Question 5.
A mixture of hydrogen and chlorine reacts normally with each other in direct sunlight.
Answer:
False; A mixture of hydrogen and chlorine reacts explosively with each other in direct sunlight.

Question 6.
Hydrogen reacts with metal oxides to give the corresponding metals.
Answer:
True

Question 7.
A substance that brings about reduction or reduces another substance is called a reducing agent.
Answer:
False; A substance that brings about reduction or reduces another substance is called an oxidizing agent.

E. Complete and balance the following equations

1. Ca + H₂O →
2. Fe + HCl →
3. Al + KOH →
4. Pb + NaOH →
5. Zn + H₂SO₄ →
6. CO + H₂ + H₂O →
Answer:
1. Ca + 2H₂O → Ca(OH)₂ + H₂↑
2. Fe + 2HCl → FeCl₂ + H₂↑
3. 2Al + 2KOH + 2H₂O → 2KAlO₂ + 3H₂↑
4. Pb + 2NaOH → Na₂PbO₂ + H₂↑
5. Zn + H₂SO₄ → ZnSO₂ + H₂↑
6. CO + H₂ + H₂O → CO₂ + 2H₂ + heat

F. Answer the following in short

Question 1.
What is an electrolytic cell?
Answer:
An electrolytic cell is a device in which electrical energy is converted into chemical energy or vice versa.

Question 2.
Differentiate between a cathode and an anode.
Answer;
The electrode connected to the positive terminal of an electrolytic cell is called the anode.
The electrode connected to the negative terminal is called the cathode.

Question 3.
What is the effect of hydrogen on litmus paper?
Answer:
Hydrogen does not affect the colour of moist blue or red litmus paper.

Question 4.
What happens if hydrogen reacts with chlorine in direct sunlight?
Answer:
In direct sunlight, the reaction of hydrogen with chlorine occurs with an explosion.

Question 5.
Differentiate between oxidation and reduction.
Answer:
A chemical process that involves the addition of oxygen or the removal of hydrogen is called oxidation. A chemical process that involves the addition of hydrogen or the removal of oxygen is called reduction.

Question 6.
What is the hydrogenation of vegetable oils?
Answer:
Hydrogention is a process in which vegetable oils are converted into solid vegetable ghee (vanaspati ghee) on heating with hydrogen in the presence of nickel as a catalyst.

G Answer the following in detail

Question 1.
Write about the preparation of hydrogen by the action of cold water, hot water and steam on metals.
Answer:
By the action of water and steam on metals From cold water Active metals such as potassium, sodium and calcium react with cold water to liberate hydrogen gas and form the corresponding metal hydroxides.

From hot water : Magnesium liberates hydrogen from boiling water, but the reaction is slow.

From steam : When steam is passed over heated magnesium, aluminium, zinc and iron, hydrogen gas is produced along with the metal oxides.

Question 2.
Describe the action of alkalis on metals with the help of reactions.
Answer:
By the action of alkalis on metals :
Metals such as lithium, sodium and potassium are called alkali metals. The hydroxides of these metals such as NaOH and KOH are called alkalis. Metals like zinc, lead and aluminium react with a hot alkali solution of sodium hydroxide or potassium hydroxide to liberate hydrogen gas.

Question 3.
Describe the industrial preparation of hydrogen by the electrolysis of water.
Answer:
Industrial preparation of hydrogen by the electrolysis of water Hydrogen is produced when an electric current is passed through water. A few drops of dilute sulphuric acid or a few pellets of sodium hydroxide are added to water to make it a better conductor of electricity. This process is called electrolysis of water.

Here, acidified water is an electrolyte. There are some compounds that conduct electricity in their aqueous solution or molten state to undergo decomposition into ions. When electric current using a cell or battery is passed through the electrodes of an electrolytic cell. In electrolysis of water, oxygen is produced at the anode and hydrogen is produced at the cathode.

Question 4.
Write about the preparation of hydrogen by Bosch’s process.
Answer:
Preparation of hydrogen by Bosch’s process Bosch’s process involves the following steps.
Step 1 : Production of water gas steam is passed over hot coke at 1000°C in a converter to produce water gas (CO + H₂). The reaction is endothermic.

Step 2 : Separation of hydrogen Steam is mixed with water gas and passed over heated iron (III) oxide (Fe₂O₃) and chromium (III) oxide (Cr₂O₃) at 450-500 °C to get a mixture of carbon dioxide and hydrogen. The reaction is exothermic.

Step 3 : Removal of carbon dioxide and unreacted carbon monoxide’from the above mixture.
Removal of carbon dioxide: The mixture of CO₂ + H₂ is passed through cold water or a solution of caustic potash under pressure, which dissolves carbon dioxide leaving behind hydrogen.

Removal of carbon monoxide: The mixture is passed through a solution of ammoniacal copper(I) chloride, which dissolves the unreacted carbon monoxide. Thus, hydrogen has is left behind.

Question 5.
Write three important uses of hydrogen.
Answer:
Uses of hydrogen are :
1. For cutting and welding metals – when a mixture of hydrogen and oxygen is burnt. It gives a very hot flame called oxy-hydrogen flame which is used for cutting and welding metals.
2. As a fuel – liquid hydrogen is used as a fuel in rockets and guided missiles.
3. For the hydrogenation of vegetable oils – liquid vegetable oils are converted into solid vegetable ghee on treating with hydrogen in the presence of nickel as a catalyst.
4. In the manufacture of chemicals like ammonia (NH₃) through the Haber process, methane (CH₄) and hydrochloric acid (HCl).

H. Draw labelled diagrams of the following

Question 1.
To show the laboratory preparation of hydrogen
Answer:
Laboratory preparation of hydrogen gas

Question 2.
To show the process of electrolysis
Answer:
Process of electrolysis cathode

Think And Answer

Question 1.
Hydrogen is collected by the downward displacement of water. Why?
Answer:
The hydrogen gas is collected in the gas jar by the downward displacement of water. This is possible because hydrogen is insoluble in water and also lighter than it.

Question 2.
The complete apparatus in the laboratory preparation of hydrogen should be made airtight Why?
Answer:
Hydrogen forms an explosive mixture with air. Hence, the complete apparatus should be made airtight preventing any leakage of the gas.

Living Science Chemistry Class 8 ICSE Solutions