2. Number of
particles
Number of Avogadro
Moles c onstant
Particles= Atoms, molecules, ions
Avogadro constant = 6.02 x 1023
(Mary No Car)
1. Number Of Particles = number of moles x Avogadro constant
2. Number Of Moles = number of particles ÷ Avogadro constant
3. RECALL BACK….
1 mole of Carbon = 6.02 x 1023 atoms
1 mole of H20 = 6.02 x 1023 molecules
1 mole of Fe2+ = 6.02 x 1023 ions
1 mole of O2 = 6.02 x 1023 molecules
= 2 x 6.02 x 1023 atoms
4. CALCULATE THE NUMBER OF ATOMS IN 3 MOL
OF COPPER ATOMS.
Cu
Number of Atoms
= Number of mole x Avogadro Constant
= 3 x 6.02 x 1023
= 1.806 x 1024 mol of copper atoms
5. CALCULATE THE NUMBER OF MOLECULE IN 0.5
MOL OF CO2
O
C
O
Number of molecule
= Number of mole x Avogadro Constant
= 0.5 x 6.02 x 1023
= 3.01 x 1022 mol of carbon dioxide
6. Calculate the number of Ions in 0.5 mol
of Pb2+
Pb2+
Number of ions
= Number of mole x Avogadro Constant
= 0.4 x 6.02 x 1023
= 2.408 x 1022 mol of Pb2+
7. CALCULATE THE NUMBER OF ATOMS IN 0.5 MOL
OF CO2
O
C
Number of atoms O
= Number of mole x Avogadro Constant
= 3 x 0.5 x 6.02 x 1023
= 9.03 x 1023 mol of carbon dioxide
atoms
8. EXAMPLE 2:
a. Calculate the number of moles of atoms in 1.204 x
1025 iron atoms.
b. Calculate the number of moles of ions in 6.02 x
1021 copper(II) ions, ____
c. Given 1.505 x 1024 oxygen gas, , calculate
i) the number of moles of oxygen molecules,
ii) the number of atoms of oxygen atoms
d. Given 2.408 x 1025 hydrogen atoms, calculate
i) the number of moles of hydrogen atoms.
ii) the number of moles of hydrogen molecules,
9. A.CALCULATE THE NUMBER OF MOLES OF
ATOMS IN 1.204 X 1025 IRON ATOMS.
Number of Moles
= Number of particles
Avogadro Constant
= 1.204 x 1025
6.02 x 1023
= 20 mol of iron atoms
10. B.CALCULATE THE NUMBER OF MOLES OF IONS IN
6.02 X 1021 COPPER(II) IONS, ____
Number of Moles
= Number of particles
Avogadro Constant
= 6.02 x 1021
6.02 x 1023
= 0.01 mol of copper(II) ions
11. C. GIVEN 1.505 X 1024 OXYGEN GAS, , CALCULATE
I) THE NUMBER OF MOLES OF OXYGEN MOLECULES,
Number of Moles
= Number of particles
Avogadro Constant
= 1.505 x 1024
6.02 x 1023
= 2.5 mol of Oxygen molecules
12. C. GIVEN 1.505 X 1024 OXYGEN GAS, , CALCULATE
II) THE NUMBER OF ATOMS OF OXYGEN ATOMS
2 x 1.505 x 1024
= 3.01 x 1024 oxygen atoms
O
O O
O O
O O
O
1 O2 molecule = 2 O atoms
13. D. GIVEN 2.408 X 1025 HYDROGEN ATOMS, CALCULATE
I) THE NUMBER OF MOLES OF HYDROGEN ATOMS.
II) THE NUMBER OF MOLES OF HYDROGEN MOLECULES,
i) Number of Moles
= Number of particles
Avogadro Constant
= 2.408 x 1025
6.02 x 1023
H
= 40 mol of hydrogen atoms H
ii) 40 mol of hydrogen atoms
÷2 H
= 40 H
= 20 mol of hydrogen molecules
14. NOTE:
The gases which exist as diatomic molecules are:
O2 H2 N2 Cl2 Br2 I2
Cl
Cl
O
H
O H
I I
15. 3.3 THE MOLE AND THE MASS OF SUBSTANCES
A. The molar mass
- is the mass of one mole of any substance.
The molar mass of a substance = the mass of
1 mole
_______ of substance = the mass of
____________ particles.
-the unit of molar mass is ________.
12
1 mol of carbon-12 has a mass of exactly _____g.
12
So, the molar mass of carbon-12 is __________.
16. THE MOLAR MASS OF ALL THE OTHER SUBSTANCES
ARE NUMERICALLY EQUAL TO THEIR RELATIVE
MASSES.
Examples:
The relative atomic mass of sodium = 23, so, the
23
molar mass of sodium = ____________
The relative atomic mass of water, so, the molar
18
mass of water = ____________
17. Mass
Number of Relative
atomic
Moles Mass/ RMM
(Mario Miss Rainbow)
18. EXAMPLE 1:
a. Calculate the mass of 2 mol of carbon atoms
b. Calculate the mass of 5 mol of oxygen gas,
c. calculate the mass 0.4 mol of magnesium oxide,
MgO.
19. CALCULATE THE MASS OF 2 MOL OF
CARBON ATOMS
The molar mass of carbon atoms = 12gmol-1
so, the mass of 2 mol of carbon atoms
= 2 mol x 12gmol-1
= 24g
20. CALCULATE THE MASS OF 5 MOL OF
OXYGEN GAS
the mass of 5 mol of oxygen gas
= 5 mol x 32gmol-1
= 160g
21. Calculate the mass 0.4 mol of magnesium oxide, MgO.
The molar mass of MgO = 24+16 = 40gmol-1
The mass of 0.4 mol of magnesium oxide
= 0.4 mol x 40gmol-1
= 16g
22. ANSWER
a) The molar mass of carbon atoms = 12gmol-1
so, the mass of 2 mol of carbon atoms
= 2 mol x 12gmol-1
= 24g
b) The molar mass of oxygen gas = 2(16) = 32gmol-1
so, the mass of 5 mol of carbon atoms
=5 mol x 32gmol-1
= 160g
c) The molar mass of MgO = 24+16 = 40gmol-1
so, the mass of 0.4 mol of MgO
= 0.4 mol x 40gmol-1
= 16g
23. EXAMPLE 2:
a. How many moles of atoms are there in 18g of
carbon?
b. How many moles of sodium chloride are there in
14.625g of sodium chloride, NaCl?
c. Given 6.4g of oxygen gas, calculate
i) the number of moles of oxygen gas.
ii) the number of moles of oxygen atoms.
24. How many moles of atoms are there in 18g of carbon?
The molar mass of carbon atoms = 12gmol-1
The number of moles of carbon atoms = 18 g
12gmol-1
= 1.5mol
25. How many moles of sodium chloride are there in
14.625g of sodium chloride, NaCl?
The molar mass of sodium chloride, NaCl
= 23 + 35.5=58.5gmol-1
So, the number of moles of NaCl =14.635 g
58.5gmol-1
=0.25mol
26. O
Given 6.4g of oxygen gas, calculate
i) the number of moles of oxygen gas. O
The molar mass of Oxygen gas = 2(16) = 32gmol-1
So, the number of moles of oxygen gas = 6.4 g
32gmol-1
= 0.2mol
27. II) THE NUMBER OF MOLES OF OXYGEN ATOMS.
ii) The number of moles of oxygen atoms O
= 2 x 0.2 mol = 0.4 mol
O
28. ANSWER:
a) The molar mass of carbon atoms = 12gmol-1
The number of moles of carbon atoms = 18 g
12gmol-1
= 1.5mol
b) The molar mass of sodium chloride, NaCl = 23 + 35.5 = 58.5gmol-1
So, the number of moles of carbon atoms=14.635 g
58.5gmol-1
= 0.25mol
b) i) The molar mass of Oxygen gas = 2(16) = 32gmol-1
So, the number of moles of oxygen gas = 6.4 g
32gmol-1
= 0.2mol
ii) The number of moles of oxygen atoms
= 2 x 0.2 mol = 0.4 mol
29. EXAMPLE 3:
a. Calculate the mass of 6.02x 1021 iron atoms.
b. How many molecules of oxygen are there in 12.8
g of oxygen gas?
30. a. Calculate the mass of 6.02x 1021 iron
atoms. Fe
Number of moles
= 6.02 x 1021
6.02 x 1023
= 0.01 mol
The mass of 6.02x 1021 iron atoms
= 0.01mol x 56gmol-1
= 0.56g
31. How many molecules of oxygen are thereO
in 12.8 g of oxygen gas?
Number of moles O
= 12.8 g
32gmol-1
= 0.4 mol
Number of molecule of oxygen
= 0.4 x 6.02 x 1023
= 2.408 x 1023 molecules of oxygen
32. ANSWER:
a. 6.02 x 1021 iron atoms = 6.02 x 1021
6.02 x 1023
= 0.01 mol
0.01 mol of iron atoms = 0.01mol x 56gmol-1 = 0.56g
b) 12.8g of oxygen gas = 12.8 g
32gmol-1
= 0.4 mol
0.4mol of oxygen gas = 0.4 x 6.02 x 1023
= 2.408 x 1023 molecules of oxygen