Selina Textbook Solutions: Mole Concept and Stoichiometry | Chemistry Class 10 ICSE PDF Download

 Page 1


Exercise 5(A) 
Solution 1. 
(a) Gay-Lussac’s law states that when gases react, they do so in volumes which bear a 
simple ratio to one another, and to the volume of the gaseous product, provided that all 
the volumes are measured at the same temperature and pressure. 
(b) Avogadro’s law states that equal volumes of all gases under similar conditions of 
temperature and pressure contain the same number of molecules. 
Solution 2. 
a) The number of atoms in a molecule of an element is called its atomicity. Atomicity of 
Hydrogen is 2, phosphorus is 4 and sulphur is 8. 
b) N 2means 1 molecule of nitrogen and 2N means two atoms of nitrogen. 
N 2 can exist independently but 2N cannot exist independently. 
Solution 3. 
(a) This is due to Avogadros Law which states Equal volumes of all gases under similar 
conditions of temperature and pressure contain the same number of molecules. 
Now volume of hydrogen gas =volume of helium gas 
n molecules of hydrogen =n molecules of helium gas 
nH 2=nHe 
1 mol. of hydrogen has 2 atoms of hydrogen and I molecule of helium has 1 atom of 
helium 
Therefore 2H=He 
Therefore atoms in hydrogen is double the atoms of helium. 
(b) For a given volume of gas under given temperature and pressure, a change in any 
one of the variable i.e., pressure or temperature changes the volume. 
(c) Inflating a balloon seems violating Boyles law as volume is increasing with increase 
in pressure. Since the mass of gas is also increasing. 
 
Chapter 5 - Mole Concept and Stoichiometry
Page 2


Exercise 5(A) 
Solution 1. 
(a) Gay-Lussac’s law states that when gases react, they do so in volumes which bear a 
simple ratio to one another, and to the volume of the gaseous product, provided that all 
the volumes are measured at the same temperature and pressure. 
(b) Avogadro’s law states that equal volumes of all gases under similar conditions of 
temperature and pressure contain the same number of molecules. 
Solution 2. 
a) The number of atoms in a molecule of an element is called its atomicity. Atomicity of 
Hydrogen is 2, phosphorus is 4 and sulphur is 8. 
b) N 2means 1 molecule of nitrogen and 2N means two atoms of nitrogen. 
N 2 can exist independently but 2N cannot exist independently. 
Solution 3. 
(a) This is due to Avogadros Law which states Equal volumes of all gases under similar 
conditions of temperature and pressure contain the same number of molecules. 
Now volume of hydrogen gas =volume of helium gas 
n molecules of hydrogen =n molecules of helium gas 
nH 2=nHe 
1 mol. of hydrogen has 2 atoms of hydrogen and I molecule of helium has 1 atom of 
helium 
Therefore 2H=He 
Therefore atoms in hydrogen is double the atoms of helium. 
(b) For a given volume of gas under given temperature and pressure, a change in any 
one of the variable i.e., pressure or temperature changes the volume. 
(c) Inflating a balloon seems violating Boyles law as volume is increasing with increase 
in pressure. Since the mass of gas is also increasing. 
 
Chapter 5 - Mole Concept and Stoichiometry
Solution 4. 
2H 2 + O 2 ? 2H 2O 
2 V     1V         2V 
From the equation, 2V of hydrogen reacts with 1V of oxygen 
so 200cm
3
 of Hydrogen reacts with = 200/2= 100 cm
3 
Hence, the unreacted oxygen is 150 – 100 = 50cm
3 
of oxygen. 
Solution 5. 
 
Solution 6. 
 
Solution 7. 
Page 3


Exercise 5(A) 
Solution 1. 
(a) Gay-Lussac’s law states that when gases react, they do so in volumes which bear a 
simple ratio to one another, and to the volume of the gaseous product, provided that all 
the volumes are measured at the same temperature and pressure. 
(b) Avogadro’s law states that equal volumes of all gases under similar conditions of 
temperature and pressure contain the same number of molecules. 
Solution 2. 
a) The number of atoms in a molecule of an element is called its atomicity. Atomicity of 
Hydrogen is 2, phosphorus is 4 and sulphur is 8. 
b) N 2means 1 molecule of nitrogen and 2N means two atoms of nitrogen. 
N 2 can exist independently but 2N cannot exist independently. 
Solution 3. 
(a) This is due to Avogadros Law which states Equal volumes of all gases under similar 
conditions of temperature and pressure contain the same number of molecules. 
Now volume of hydrogen gas =volume of helium gas 
n molecules of hydrogen =n molecules of helium gas 
nH 2=nHe 
1 mol. of hydrogen has 2 atoms of hydrogen and I molecule of helium has 1 atom of 
helium 
Therefore 2H=He 
Therefore atoms in hydrogen is double the atoms of helium. 
(b) For a given volume of gas under given temperature and pressure, a change in any 
one of the variable i.e., pressure or temperature changes the volume. 
(c) Inflating a balloon seems violating Boyles law as volume is increasing with increase 
in pressure. Since the mass of gas is also increasing. 
 
Chapter 5 - Mole Concept and Stoichiometry
Solution 4. 
2H 2 + O 2 ? 2H 2O 
2 V     1V         2V 
From the equation, 2V of hydrogen reacts with 1V of oxygen 
so 200cm
3
 of Hydrogen reacts with = 200/2= 100 cm
3 
Hence, the unreacted oxygen is 150 – 100 = 50cm
3 
of oxygen. 
Solution 5. 
 
Solution 6. 
 
Solution 7. 
 
Solution 8. 
 
Solution 9. 
 
 
Solution 10. 
 
Solution 11. 
C 3H 8 + 5O 2 ? 3CO 2 + 4H 2O 
1 V 5 V 3 V 
From equation, 5 V of O 2 required = 1V of propane 
so, 100 cm
3
 of O 2 will require = 20 cm
3
 of propane 
Page 4


Exercise 5(A) 
Solution 1. 
(a) Gay-Lussac’s law states that when gases react, they do so in volumes which bear a 
simple ratio to one another, and to the volume of the gaseous product, provided that all 
the volumes are measured at the same temperature and pressure. 
(b) Avogadro’s law states that equal volumes of all gases under similar conditions of 
temperature and pressure contain the same number of molecules. 
Solution 2. 
a) The number of atoms in a molecule of an element is called its atomicity. Atomicity of 
Hydrogen is 2, phosphorus is 4 and sulphur is 8. 
b) N 2means 1 molecule of nitrogen and 2N means two atoms of nitrogen. 
N 2 can exist independently but 2N cannot exist independently. 
Solution 3. 
(a) This is due to Avogadros Law which states Equal volumes of all gases under similar 
conditions of temperature and pressure contain the same number of molecules. 
Now volume of hydrogen gas =volume of helium gas 
n molecules of hydrogen =n molecules of helium gas 
nH 2=nHe 
1 mol. of hydrogen has 2 atoms of hydrogen and I molecule of helium has 1 atom of 
helium 
Therefore 2H=He 
Therefore atoms in hydrogen is double the atoms of helium. 
(b) For a given volume of gas under given temperature and pressure, a change in any 
one of the variable i.e., pressure or temperature changes the volume. 
(c) Inflating a balloon seems violating Boyles law as volume is increasing with increase 
in pressure. Since the mass of gas is also increasing. 
 
Chapter 5 - Mole Concept and Stoichiometry
Solution 4. 
2H 2 + O 2 ? 2H 2O 
2 V     1V         2V 
From the equation, 2V of hydrogen reacts with 1V of oxygen 
so 200cm
3
 of Hydrogen reacts with = 200/2= 100 cm
3 
Hence, the unreacted oxygen is 150 – 100 = 50cm
3 
of oxygen. 
Solution 5. 
 
Solution 6. 
 
Solution 7. 
 
Solution 8. 
 
Solution 9. 
 
 
Solution 10. 
 
Solution 11. 
C 3H 8 + 5O 2 ? 3CO 2 + 4H 2O 
1 V 5 V 3 V 
From equation, 5 V of O 2 required = 1V of propane 
so, 100 cm
3
 of O 2 will require = 20 cm
3
 of propane 
Solution 12. 
 
Solution 13. 
2CO + O 2 ? 2CO 2 
2 V 1 V 2 V 
2 V of CO requires = 1V of O 2 
so, 100 litres of CO requires = 50 litre of O 2 
Solution 14. 
 
Solution 15. 
H 2 + Cl 2 ? 2HCl 
1V 1V 2 V 
Since 1 V hydrogen requires 1 V of oxygen and 4cm
3
 of H 2 remained behind so the 
mixture had com”>16 cm
3
 hydrogen and 16 cm
3 
chlorine. 
Therefore Resulting mixture is H 2 =4cm
3
,HCl=32cm
3
 
Page 5


Exercise 5(A) 
Solution 1. 
(a) Gay-Lussac’s law states that when gases react, they do so in volumes which bear a 
simple ratio to one another, and to the volume of the gaseous product, provided that all 
the volumes are measured at the same temperature and pressure. 
(b) Avogadro’s law states that equal volumes of all gases under similar conditions of 
temperature and pressure contain the same number of molecules. 
Solution 2. 
a) The number of atoms in a molecule of an element is called its atomicity. Atomicity of 
Hydrogen is 2, phosphorus is 4 and sulphur is 8. 
b) N 2means 1 molecule of nitrogen and 2N means two atoms of nitrogen. 
N 2 can exist independently but 2N cannot exist independently. 
Solution 3. 
(a) This is due to Avogadros Law which states Equal volumes of all gases under similar 
conditions of temperature and pressure contain the same number of molecules. 
Now volume of hydrogen gas =volume of helium gas 
n molecules of hydrogen =n molecules of helium gas 
nH 2=nHe 
1 mol. of hydrogen has 2 atoms of hydrogen and I molecule of helium has 1 atom of 
helium 
Therefore 2H=He 
Therefore atoms in hydrogen is double the atoms of helium. 
(b) For a given volume of gas under given temperature and pressure, a change in any 
one of the variable i.e., pressure or temperature changes the volume. 
(c) Inflating a balloon seems violating Boyles law as volume is increasing with increase 
in pressure. Since the mass of gas is also increasing. 
 
Chapter 5 - Mole Concept and Stoichiometry
Solution 4. 
2H 2 + O 2 ? 2H 2O 
2 V     1V         2V 
From the equation, 2V of hydrogen reacts with 1V of oxygen 
so 200cm
3
 of Hydrogen reacts with = 200/2= 100 cm
3 
Hence, the unreacted oxygen is 150 – 100 = 50cm
3 
of oxygen. 
Solution 5. 
 
Solution 6. 
 
Solution 7. 
 
Solution 8. 
 
Solution 9. 
 
 
Solution 10. 
 
Solution 11. 
C 3H 8 + 5O 2 ? 3CO 2 + 4H 2O 
1 V 5 V 3 V 
From equation, 5 V of O 2 required = 1V of propane 
so, 100 cm
3
 of O 2 will require = 20 cm
3
 of propane 
Solution 12. 
 
Solution 13. 
2CO + O 2 ? 2CO 2 
2 V 1 V 2 V 
2 V of CO requires = 1V of O 2 
so, 100 litres of CO requires = 50 litre of O 2 
Solution 14. 
 
Solution 15. 
H 2 + Cl 2 ? 2HCl 
1V 1V 2 V 
Since 1 V hydrogen requires 1 V of oxygen and 4cm
3
 of H 2 remained behind so the 
mixture had com”>16 cm
3
 hydrogen and 16 cm
3 
chlorine. 
Therefore Resulting mixture is H 2 =4cm
3
,HCl=32cm
3
 
Solution 16. 
CH 4 + 2O 2 ? CO 2 + 2H 2O 
1 V 2 V 1 V 
2C 2H 2 + 5O 2 ? 4CO 2 + 2H 2O 
2 V 5 V 4 V 
From the equations, we can see that 
1V CH 4 requires oxygen = 2 V O 2 
So, 10cm
3
 CH 4 will require =20 cm
3
 O 2 
Similarly 2 V C 2H 2 requires = 5 V O 2 
So, 10 cm
3
 C 2H 2 will require = 25 cm
3
 O 2 
Now, 20 V O 2 will be present in 100 V air and 25 V O 2 will be present in 125 V air ,so the 
volume of air required is 225cm
3
 
Solution 17. 
 
Solution 18.