The document explains relative atomic mass (RAM), relative molecular mass (RMM), and relative formula mass (RFM), emphasizing carbon-12 as a standard for comparisons. It details concepts related to moles, Avogadro's constant, and calculations involving mass, number of particles, and volume of gases at standard and room conditions. The document also covers empirical and molecular formulas, illustrating how to determine empirical formulas through chemical reactions.

6. A. Relative Atomic Mass and Relative
Molecular Mass
• Based on the theory of particles:
particles are very small and discrete. A single atom
is too small and light and cannot be weighed directly
• Thus, the mass of an atom is obtained by comparing
it with another atom which is taken as a standard.

7. Which element is chosen as
standard atom and why?

8. Carbon-12 is chosen as a standard because:
• Carbon exists as a solid at room temperature
• Carbon can be handled easily
• Carbon has an accurate mass

9. Relative atomic mass, RAM
• Meaning;
The average mass of one atom of the element
when compared with 1/12 of the mass of an
atom of carbon-12.

12. • Example:
RAM of magnesium
= 24 = 24
1/12 x 12
= magnesium is 24 times larger than carbon-12
** THE VALUE OF NUCLEON NUMBER IN THE
PERIODIC TABLE OF ELEMENT
= RELATIVE ATOMIC MASS, RAM

13. PERIODIC TABLE

14. Relative molecular mass, RMM
• Meaning;
The average mass of one molecule when compared
with 1/12 of the mass of an atom of carbon-12.
Relative Molecular Mass, RMM
= Average mass of one molecule
1/12 x the mass of an atom of carbon-12
• Calculate RMM by adding up the relative atomic mass
of all the atoms that present in the molecule

16. Carbon dioxide
Relative molecular mass, RMM

17. Glucose
Relative molecular mass, RMM

18. Relative formula mass, RFM
• Meaning;
The average mass of an ionic substance when
compared with 1/12 of the mass of an atom of
carbon-12.
Relative Molecular Mass, RMM
= Average mass of an ionic substance
1/12 x the mass of an atom of carbon-12
• Calculate RFM by adding up the relative atomic mass
of all the atoms that present in the ionic compound

19. Relative formula mass, RFM
Zinc chloride

20. Relative formula mass, RFM
Aluminium sulphate

21. Relative formula mass, RFM
Iron(III) oxide

23. Try this
1

24. Try this
2

28. one pair of shoes =??shoe
one dozen of beer=?? beer
One mole of atom=??? atom

29. 602000000000000000000000
particles (atom/molecule/ion)
Avogadro constant,

30. The Mole and the Number of Particles
• The number of particles in matter is measured
in mole.
• Definition:
The amount of substance that contains as
many particles as the number of atoms in
exactly 12 g of carbon-12
• Symbol of mole: mol

31. How many atoms are there in 12 g of carbon-12?
= 6.02 × 1023
• The value of 6.02 × 1023 is called the Avogadro
constant or Avogadro number
• Avogadro constant, NA
The number of particles in one mole of a
substance

32. Point to note:
One mole of any substance contains 6.02 × 1023
particles
1 mol of atomic substance contains 6.02 × 1023
atoms
 1 mol of molecular substance contains 6.02 × 1023
molecules
 1 mol of ionic substance contains 6.02 × 1023 ions

34. Relationship between the number of moles and
the number of particles (atoms/molecules/ions)
Number of moles,
(mol)
Number of particles
(atoms, molecules, ions)
× NA
÷ NA

35. Number of
particles
Moles NA

36. Example 1:
A closed glass bottle contains 0.5 mol of oxygen
gas, O2
(a) How many oxygen molecules, O2 are there in
the bottle?
oxygen atoms
(b)How many are there in the
bottle?
[Avogadro constant: 6.02 × 1023 mol-1]

37. a) The number of oxygen molecules, O2
= 0.5 mol × 6.02 × 1023 mol-1
= 3.01 × 1023 molecules
b) The number of oxygen atoms
= 0.5 mol × 6.02 × 1023 mol-1 × 2
= 6.02 × 1023 atoms
Number of
particles
Moles NA

38. Number of
particles
Moles NA

39. Number of
particles
Moles NA

42. The Mole and the Mass of Substances
• The mass of one mole of any substance is
called molar mass
• Units: g mol-1
• The molar mass of substances are numerically
equal to relative mass

43. Element Relative mass
Mass of
1 mol
Molar mass
Helium 4 4 4 g mol-1
Sodium 23 23 23 g mol-1
Water, H2O 2(1) + 16 = 18 18 18 g mol-1
Ammomia, NH3 14 + 3(1) = 17 17 17 g mol-1

44. Relationship between the number of moles and
the mass of a substance
Number of moles,
(mol)
Mass
(g)
× molar mass
÷ molar mass

45. Mass
(g)
Moles
RAM /
RMM /
RFM

46. Example 1:
What is the mass of
0.1 mol
2.408 × 1023 atoms
(a) of magnesium?
(b) of magnesium?
[Relative atomic mass: Mg=24; Avogadro
constant: 6.02 × 1023 mol-1]

47. (b) The number of moles Mg atoms
= 2.408 × 1023
6.02 × 1023 mol-1
= 0.4 mol
Mass of Mg atoms
= 0.4 mol × 24 g mol-1 = 9.6 g
(a) Molar mass of Mg = 24 g mol-1
Mass of Mg = 0.1 mol × 24 g mol-1
= 2.4 g
Mass (g)
Moles
RAM /
RMM /
RFM
Number of
particles
Moles NA

48. Example 2:
RMM of SO2
= 32 + 2(16) = 64
Molar mass of SO2 = 64 g mol-1
The number of moles
= 16 g
64 g mol-1
= 0.25 mol
Mass (g)
Moles
RAM /
RMM /
RFM
How many moles of molecules are there in 16 g of sulphur
dioxide gas, SO2?
[Relative atomic mass: O=16, S=32]

50. The Mole and the Volume of Gas

51. Relationship between the number of moles and
the volume of gas
Number of moles,
(mol)
Volume of gas
(dm3)
× molar volume
÷ molar volume

52. Volume
(dm3)
Moles
22.4 dm3
(STP) /
24 dm3 (room
condition)

53. volume of 1.2 mol
What is the of ammonia gas,
NH3 at STP?
[Molar volume: 22.4 dm3 mol-1 at STP]
Example 1:
Volume
(dm3)
Moles
3
22.4 dm
(STP) /
24 dm3 (RC)
The volume of ammonia gas, NH3
= 1.2 mol × 22.4 dm3 mol-1
= 26.88 dm3

54. How many moles of ammonia gas, NH3 are present
in 600 cm3 of the gas measured at room conditions?
[Molar volume: 24 dm3 mol-1 at room condition]
Example 2:
Volume
(dm3)
Moles
3
22.4 dm
(STP) /
24 dm3 (RC)
The number of moles of ammonia gas, NH3
= 600 cm3
1000
= 0.6 dm3
= 0.6 dm3
24 dm3 mol-1
= 0.025 mol

55. Relationship between the number of moles, number of
particles, mass and the volume of gas

61. H2
Symbol of
hydrogen atom
Shows that there are
two hydrogen atom
in a hydrogen gas,
H2 molecule

62. Symbol of
hydrogen atom
H2O
Shows that there are
two hydrogen atom
in a water molecule
Symbol of
oxygen atom
Shows that there are
one oxygen atom in
a water molecule

63. • Compound can be represented by two types:
1. Empirical formula
- Chemical formula that shows the simplest
ratio of the number of atoms of each
element in a compound.
2. Molecular formula
- Chemical formula that shows the actual
number of atoms of each element found in a
molecule of a compound

68. To determine empirical formula of magnesium
oxide
Burn magnesium with oxygen
To determine empirical formula copper(II) oxide
Use hydrogen to removed oxygen from
copper(II) oxide
Weigh mass of copper

77. Try this..

83. Qualitative aspect:
- Identify the reactant and product
- Physical states
-

84. Quantitative aspect:
- Ratio of substances involved
-

90. Solving steps
Step 1: Find the mole
Step 2: Compare the mole ratio
Step 3: Find the value