Page 10 - 1202 Question Bank Chemistry Form 4 KSSM

3 The Mole Concept, Chemical
Chapter Formula and Equation

NOTES

3.1 Relative Atomic Mass and 2. Avogadro constant, N is defined as the number of
A
Relative Molecular Mass particles in one mole of a substance. In other words,
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1 mol of substance contains 6.02 × 10 particles that
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1. The mass of an atom when compared to a standard form the substance.
atom is called relative atomic mass, RAM. Relative 3. When we say, 2 pairs of shoes, it means 2 × 2 = 4
atomic mass has no unit because it is not the actual shoes. If we were to say 2 dozen of shoes, that means
mass but only a comparison value. 2 × 12 = 24 shoes.
4. What if we say 2 moles of shoes? It means 2 × 6.02 ×
Standard atom Why is it chosen 10 = 1.204 × 10 shoes.
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Carbon-12 • Carbon-12 was used as the × N
The mass of one reference standard in mass A
carbon-12 atom spectrometers. Number of
was assigned • Most elements combine with Number of particles Number of moles, n
12 units. carbon-12. moles, n Atom // = Number of particles
• Exists as a solid at room molecule // N A
temperature and easy ion
to handle. ÷ N
A
2. Based on the carbon-12 scale, the relative atomic 5. The molar mass is the mass of one mole of the
mass of an element is the average mass of one atom substance.
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of the element when compared with 12 of the mass 6. The molar mass of a substance contains 6.02 × 10
of one carbon-12 atom. particles of the substance.
7. The unit of molar mass is g mol .
–1
Relative atomic mass (RAM)
Average mass of one atom of the element × molar mass
= 1 Number of moles, n
× Mass of one carbon – 12 atom Number of
12 Mass Mass
moles, n = Molar mass
3. Relative molecular mass of a molecule is defined as ÷ molar mass
the average mass of the molecule when compared
1
with of the mass of one carbon-12 atom. 8. The molar volume of a gas is the volume occupied
12 by one mole of the gas or 6.02 × 10 particles
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Relative molecular mass (RMM) of the gas.
–1
3
Average mass of one molecule 9. The unit of molar volume is dm mol .
= 1 10. Under the same temperature and pressure, an equal
× Mass of one carbon – 12 atom number of moles of any gas will have the same
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volume.
4. The term ‘relative molecular mass’ can only be used 11. The molar volume depends on the conditions.
for substances that are made up of molecules.
For ionic compounds, the ‘relative formula mass Molar volume
(RFM) is used instead. Standard temperature and Room conditions:
pressure, STP: Temperature = 25 °C
3.2 Mole Concept Temperature = 0 °C Pressure =1 atm
1. One mole, with the symbol ‘mol’ of substance is Pressure = 1 atm
defined as: 22.4 dm mol –1 24 dm mol –1
3
3
Substance that contains 6.02214076 × 10 23 22400 cm mol –1 24 000 cm mol –1
3
3
elementary entities of the substance.

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