Selina Textbook Solutions: Study of The First Element – Hydrogen | Chemistry Class 9 ICSE PDF Download

 Page 1


Chapter 9. Study of the First Element – hydrogen
Exercise 9
Solution 1.
(a) The position of hydrogen in the periodic table 
 
Hydrogen is first element in the periodic table. It has an atomic number l and an atomic 
mass of 1.00794 amu, occupying group – IA. Its position is peculiar because it is 
grouped with metals although it is a non-metal properties. Hydrogen relate to Group 
IA as well as Group VII A.
(b) The properties of hydrogen resemble the properties of Group IA elements (Alkali 
metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was 
put at the top of the periodic table so that the symmetry of the modern periodic table is 
not disturbed.
1. All elements in Group- IA have one electron in outermost shell, so they 
havevalency one.
2. These elements in Group-IA are good reducing agents.
3. All elements of this group formsoxide which are highly basic and dissolves in water 
to form strong alkalis.
4. They impartcolour to a flame.
Solution 2.
Similarity of hydrogen with alkali metals and halogens
 
Similarity of hydrogen 
with alkali metals 
[Group 1 (IA)]
Similarity of hydrogen with 
halogens [Group 17 (VIIA)]
Page 2


Chapter 9. Study of the First Element – hydrogen
Exercise 9
Solution 1.
(a) The position of hydrogen in the periodic table 
 
Hydrogen is first element in the periodic table. It has an atomic number l and an atomic 
mass of 1.00794 amu, occupying group – IA. Its position is peculiar because it is 
grouped with metals although it is a non-metal properties. Hydrogen relate to Group 
IA as well as Group VII A.
(b) The properties of hydrogen resemble the properties of Group IA elements (Alkali 
metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was 
put at the top of the periodic table so that the symmetry of the modern periodic table is 
not disturbed.
1. All elements in Group- IA have one electron in outermost shell, so they 
havevalency one.
2. These elements in Group-IA are good reducing agents.
3. All elements of this group formsoxide which are highly basic and dissolves in water 
to form strong alkalis.
4. They impartcolour to a flame.
Solution 2.
Similarity of hydrogen with alkali metals and halogens
 
Similarity of hydrogen 
with alkali metals 
[Group 1 (IA)]
Similarity of hydrogen with 
halogens [Group 17 (VIIA)]
Electronic 
configuration
Electronic configuration = 
1. Thus, 1electro in the 
outermost valence shell.
  
Example: 
H=1; Li=2, 1; Na=2,8,1; 
K=2,8,8,1
One electron less than the nearest 
noble gas.
Example: 
H= 1 (He=2) 
F= 2,7 (Ne=2,8) 
Cl= 2,8,7 (Ar=2,8,8)
Ion 
formation
Electropositive character 
exhibited.
  
H 1e
–
 ? H
1+ 
Li 1e
–
 ? Li
1+ 
Na 1e
–
 ? Na
1+
Electronegative character exhibited.
  
H + 1e
–
 ? H
1- 
F + 1e
–
 ? F
1- 
Cl + 1e
–
 ? Cl
1-
Valency
Electrovalency of one 
exhibited.
  
H
1+
 , Li
1+ 
, Na
1+
Electrovalency and covalencyexhibited.
Hydrogen:
forms NaH (electrovalent)forms 
CH
4
(covalent)
Chlorine:
forms NaCl (electrovalent) 
forms CCl
4
 (covalent)
Reactions
Strong affinity for non-
metals (example: O, 
S, Cl)
  
Hydrogen: forms H
2
O; 
H
2
S; HCl
Sodium: forms Na
2
O; 
Na
2
S; NaCl
__
Reducing 
agent
Acts as a reducing agent.
  
Hydrogen:
__
Page 3


Chapter 9. Study of the First Element – hydrogen
Exercise 9
Solution 1.
(a) The position of hydrogen in the periodic table 
 
Hydrogen is first element in the periodic table. It has an atomic number l and an atomic 
mass of 1.00794 amu, occupying group – IA. Its position is peculiar because it is 
grouped with metals although it is a non-metal properties. Hydrogen relate to Group 
IA as well as Group VII A.
(b) The properties of hydrogen resemble the properties of Group IA elements (Alkali 
metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was 
put at the top of the periodic table so that the symmetry of the modern periodic table is 
not disturbed.
1. All elements in Group- IA have one electron in outermost shell, so they 
havevalency one.
2. These elements in Group-IA are good reducing agents.
3. All elements of this group formsoxide which are highly basic and dissolves in water 
to form strong alkalis.
4. They impartcolour to a flame.
Solution 2.
Similarity of hydrogen with alkali metals and halogens
 
Similarity of hydrogen 
with alkali metals 
[Group 1 (IA)]
Similarity of hydrogen with 
halogens [Group 17 (VIIA)]
Electronic 
configuration
Electronic configuration = 
1. Thus, 1electro in the 
outermost valence shell.
  
Example: 
H=1; Li=2, 1; Na=2,8,1; 
K=2,8,8,1
One electron less than the nearest 
noble gas.
Example: 
H= 1 (He=2) 
F= 2,7 (Ne=2,8) 
Cl= 2,8,7 (Ar=2,8,8)
Ion 
formation
Electropositive character 
exhibited.
  
H 1e
–
 ? H
1+ 
Li 1e
–
 ? Li
1+ 
Na 1e
–
 ? Na
1+
Electronegative character exhibited.
  
H + 1e
–
 ? H
1- 
F + 1e
–
 ? F
1- 
Cl + 1e
–
 ? Cl
1-
Valency
Electrovalency of one 
exhibited.
  
H
1+
 , Li
1+ 
, Na
1+
Electrovalency and covalencyexhibited.
Hydrogen:
forms NaH (electrovalent)forms 
CH
4
(covalent)
Chlorine:
forms NaCl (electrovalent) 
forms CCl
4
 (covalent)
Reactions
Strong affinity for non-
metals (example: O, 
S, Cl)
  
Hydrogen: forms H
2
O; 
H
2
S; HCl
Sodium: forms Na
2
O; 
Na
2
S; NaCl
__
Reducing 
agent
Acts as a reducing agent.
  
Hydrogen:
__
CuO + H
2
 ? Cu + H
2
O
Sodium:
CuO + 2Na ? Cu + Na
2
O
Atomicity __
Diatomic molecules are formed. (Two 
atoms linked by a single bond)
Hydrogen 
H:H or H-H ? H
2
 
Chlorine 
Cl:Cl or Cl-Cl ? Cl
2
Resemblance with Halogens:
1. Both exist in the form of diatomic molecules.
2. Both show gaseous nature.
3. Both have a valency of 1.
4. Both are non-metals.
5. Both lose electron to term anions.
Solution 3.
(a) Hydrogen is found in minute traces in the Earth’s crust and the Earth’s atmosphere. 
The atmosphere around the sun and stars is found to contain 1.1 % hydrogen.
(b) Henry Cavendish when prepared this gas from iron and dil. acids, he established its 
elementary nature and showed that when the gas burns in air, water is formed. It was on 
account of this property that Lavoisier in 1783 named it hydrogen (Greek word meaning 
water-former).
Solution 4.
Page 4


Chapter 9. Study of the First Element – hydrogen
Exercise 9
Solution 1.
(a) The position of hydrogen in the periodic table 
 
Hydrogen is first element in the periodic table. It has an atomic number l and an atomic 
mass of 1.00794 amu, occupying group – IA. Its position is peculiar because it is 
grouped with metals although it is a non-metal properties. Hydrogen relate to Group 
IA as well as Group VII A.
(b) The properties of hydrogen resemble the properties of Group IA elements (Alkali 
metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was 
put at the top of the periodic table so that the symmetry of the modern periodic table is 
not disturbed.
1. All elements in Group- IA have one electron in outermost shell, so they 
havevalency one.
2. These elements in Group-IA are good reducing agents.
3. All elements of this group formsoxide which are highly basic and dissolves in water 
to form strong alkalis.
4. They impartcolour to a flame.
Solution 2.
Similarity of hydrogen with alkali metals and halogens
 
Similarity of hydrogen 
with alkali metals 
[Group 1 (IA)]
Similarity of hydrogen with 
halogens [Group 17 (VIIA)]
Electronic 
configuration
Electronic configuration = 
1. Thus, 1electro in the 
outermost valence shell.
  
Example: 
H=1; Li=2, 1; Na=2,8,1; 
K=2,8,8,1
One electron less than the nearest 
noble gas.
Example: 
H= 1 (He=2) 
F= 2,7 (Ne=2,8) 
Cl= 2,8,7 (Ar=2,8,8)
Ion 
formation
Electropositive character 
exhibited.
  
H 1e
–
 ? H
1+ 
Li 1e
–
 ? Li
1+ 
Na 1e
–
 ? Na
1+
Electronegative character exhibited.
  
H + 1e
–
 ? H
1- 
F + 1e
–
 ? F
1- 
Cl + 1e
–
 ? Cl
1-
Valency
Electrovalency of one 
exhibited.
  
H
1+
 , Li
1+ 
, Na
1+
Electrovalency and covalencyexhibited.
Hydrogen:
forms NaH (electrovalent)forms 
CH
4
(covalent)
Chlorine:
forms NaCl (electrovalent) 
forms CCl
4
 (covalent)
Reactions
Strong affinity for non-
metals (example: O, 
S, Cl)
  
Hydrogen: forms H
2
O; 
H
2
S; HCl
Sodium: forms Na
2
O; 
Na
2
S; NaCl
__
Reducing 
agent
Acts as a reducing agent.
  
Hydrogen:
__
CuO + H
2
 ? Cu + H
2
O
Sodium:
CuO + 2Na ? Cu + Na
2
O
Atomicity __
Diatomic molecules are formed. (Two 
atoms linked by a single bond)
Hydrogen 
H:H or H-H ? H
2
 
Chlorine 
Cl:Cl or Cl-Cl ? Cl
2
Resemblance with Halogens:
1. Both exist in the form of diatomic molecules.
2. Both show gaseous nature.
3. Both have a valency of 1.
4. Both are non-metals.
5. Both lose electron to term anions.
Solution 3.
(a) Hydrogen is found in minute traces in the Earth’s crust and the Earth’s atmosphere. 
The atmosphere around the sun and stars is found to contain 1.1 % hydrogen.
(b) Henry Cavendish when prepared this gas from iron and dil. acids, he established its 
elementary nature and showed that when the gas burns in air, water is formed. It was on 
account of this property that Lavoisier in 1783 named it hydrogen (Greek word meaning 
water-former).
Solution 4.
(a) A monovalent metal 
2Na + H
2
 ? 2NaH 
(Sodium hydride)
(b) A divalent metal 
Ca + H
2
 ? CaH
2 
(Calcium hydride)
Solution 5.
(a) Calcium: is not used in lab preparation of hydrogen because:
1. The reaction and very violent and exothermic hence dangerous.
2. The heat liberated ignites the hydrogen.
3. Calcium is expensive.
(b) Iron: Iron reacts slowly at ordinary temperatures, hence requires heating. The 
hydrogen produced also contain impurities like sulphur dioxide and hydrogen sulphide. 
Hence, it is not used in lab preparation of hydrogen.
(c) Aluminium: It is not used in the lab preparation of hydrogen because oxides of this 
metal keep sticking to the surface of the metal. Thus the steam does not come in contact 
with metal and hence reaction stops. .
(d) Sodium: It is riot used in the lab preparation of hydrogen because the reaction is 
violent. The sodium melts into a globule and darts about freely on the surface of water 
hence the collection of hydrogen is difficult.
Solution 6.
Depending upon the nature of reaction taking place between metals and substances like 
air, water and acids, metals are arranged in a vertical series in order of their activity. 
Such a series is called activity series of metals.
The metals places near the top of the series are the most reactive, while those placed 
near the bottom are the least reactive.
When dilute hydrochloric acid or dilute sulphuric acid react with the metals above 
hydrogen in the activity series, they produce hydrogen. But the metals below hydrogen in 
the activity series do not.
Solution 7.
(a) Reactants: Nitrogen and hydrogen (Haber process)
Page 5


Chapter 9. Study of the First Element – hydrogen
Exercise 9
Solution 1.
(a) The position of hydrogen in the periodic table 
 
Hydrogen is first element in the periodic table. It has an atomic number l and an atomic 
mass of 1.00794 amu, occupying group – IA. Its position is peculiar because it is 
grouped with metals although it is a non-metal properties. Hydrogen relate to Group 
IA as well as Group VII A.
(b) The properties of hydrogen resemble the properties of Group IA elements (Alkali 
metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was 
put at the top of the periodic table so that the symmetry of the modern periodic table is 
not disturbed.
1. All elements in Group- IA have one electron in outermost shell, so they 
havevalency one.
2. These elements in Group-IA are good reducing agents.
3. All elements of this group formsoxide which are highly basic and dissolves in water 
to form strong alkalis.
4. They impartcolour to a flame.
Solution 2.
Similarity of hydrogen with alkali metals and halogens
 
Similarity of hydrogen 
with alkali metals 
[Group 1 (IA)]
Similarity of hydrogen with 
halogens [Group 17 (VIIA)]
Electronic 
configuration
Electronic configuration = 
1. Thus, 1electro in the 
outermost valence shell.
  
Example: 
H=1; Li=2, 1; Na=2,8,1; 
K=2,8,8,1
One electron less than the nearest 
noble gas.
Example: 
H= 1 (He=2) 
F= 2,7 (Ne=2,8) 
Cl= 2,8,7 (Ar=2,8,8)
Ion 
formation
Electropositive character 
exhibited.
  
H 1e
–
 ? H
1+ 
Li 1e
–
 ? Li
1+ 
Na 1e
–
 ? Na
1+
Electronegative character exhibited.
  
H + 1e
–
 ? H
1- 
F + 1e
–
 ? F
1- 
Cl + 1e
–
 ? Cl
1-
Valency
Electrovalency of one 
exhibited.
  
H
1+
 , Li
1+ 
, Na
1+
Electrovalency and covalencyexhibited.
Hydrogen:
forms NaH (electrovalent)forms 
CH
4
(covalent)
Chlorine:
forms NaCl (electrovalent) 
forms CCl
4
 (covalent)
Reactions
Strong affinity for non-
metals (example: O, 
S, Cl)
  
Hydrogen: forms H
2
O; 
H
2
S; HCl
Sodium: forms Na
2
O; 
Na
2
S; NaCl
__
Reducing 
agent
Acts as a reducing agent.
  
Hydrogen:
__
CuO + H
2
 ? Cu + H
2
O
Sodium:
CuO + 2Na ? Cu + Na
2
O
Atomicity __
Diatomic molecules are formed. (Two 
atoms linked by a single bond)
Hydrogen 
H:H or H-H ? H
2
 
Chlorine 
Cl:Cl or Cl-Cl ? Cl
2
Resemblance with Halogens:
1. Both exist in the form of diatomic molecules.
2. Both show gaseous nature.
3. Both have a valency of 1.
4. Both are non-metals.
5. Both lose electron to term anions.
Solution 3.
(a) Hydrogen is found in minute traces in the Earth’s crust and the Earth’s atmosphere. 
The atmosphere around the sun and stars is found to contain 1.1 % hydrogen.
(b) Henry Cavendish when prepared this gas from iron and dil. acids, he established its 
elementary nature and showed that when the gas burns in air, water is formed. It was on 
account of this property that Lavoisier in 1783 named it hydrogen (Greek word meaning 
water-former).
Solution 4.
(a) A monovalent metal 
2Na + H
2
 ? 2NaH 
(Sodium hydride)
(b) A divalent metal 
Ca + H
2
 ? CaH
2 
(Calcium hydride)
Solution 5.
(a) Calcium: is not used in lab preparation of hydrogen because:
1. The reaction and very violent and exothermic hence dangerous.
2. The heat liberated ignites the hydrogen.
3. Calcium is expensive.
(b) Iron: Iron reacts slowly at ordinary temperatures, hence requires heating. The 
hydrogen produced also contain impurities like sulphur dioxide and hydrogen sulphide. 
Hence, it is not used in lab preparation of hydrogen.
(c) Aluminium: It is not used in the lab preparation of hydrogen because oxides of this 
metal keep sticking to the surface of the metal. Thus the steam does not come in contact 
with metal and hence reaction stops. .
(d) Sodium: It is riot used in the lab preparation of hydrogen because the reaction is 
violent. The sodium melts into a globule and darts about freely on the surface of water 
hence the collection of hydrogen is difficult.
Solution 6.
Depending upon the nature of reaction taking place between metals and substances like 
air, water and acids, metals are arranged in a vertical series in order of their activity. 
Such a series is called activity series of metals.
The metals places near the top of the series are the most reactive, while those placed 
near the bottom are the least reactive.
When dilute hydrochloric acid or dilute sulphuric acid react with the metals above 
hydrogen in the activity series, they produce hydrogen. But the metals below hydrogen in 
the activity series do not.
Solution 7.
(a) Reactants: Nitrogen and hydrogen (Haber process)
Chemical equation: 
Observation and conditions 
Three volumes of hydrogen and one volume of nitrogen react at temperature 450
o
C-
500
o
C at the pressure of 200-900 atm, in presence of a finely divided iron which acts as 
a catalyst, and promoter molybdenum.
(b) Reactants: Chlorine and hydrogen
Chemical equation: 
Observation and conditions 
Hydrogen and chlorine (in their equal volumes) react slowly in diffused sunlight but 
reacts explosively in direct sunlight. A spontaneous reaction takes place with the release 
of a large amount of energy.
(c) Reactants: Sulphur and hydrogen
Chemical equation: 
H
2
 + S ? H
2
S 
Observation and conditions 
Hydrogen gas when passed through molten sulphur, it reacts to give another gas, 
hydrogen sulphide.
(d) Reactants: Oxygen and hydrogen
Chemical equation: 
2H
2
 + O
2
 ? 2H
2
O 
Observation and conditions 
Hydrogen burns with a pop sound in oxygen. It burns with a pale blue flame forming 
water.
Solution 8.
(a) Among the given metals Zinc is most suitable. 
(i) Copper: In case of copper, It is placed below hydrogen in the activity series. So it does 
not displace hydrogen from acid. 
Cu + HCl ? No reaction