Page 11 - Focus SPM KSSM F4 2020 - Chemistry

Chemistry Form 4 Chapter 3 The Mole Concept, Chemical Formula and Equation
SPM Highlights SPM Tips

For molecular elements such as oxygen, make sure
Which substance has a different mass with 1 mole of you read the question carefully to understand what
glucose, C H O ? is required in the question. Use RAM to calculate
6
12
6
[Relative atomic mass: H,1; C, 12; O, 16]
A 3 moles of propanol, C H OH the number of atoms of oxygen, O. Use RMM to
calculate the number of molecules of oxygen,
7
3
B 4 moles of propane, C H 6 O .
3
C 6 moles of ethane, C H 6 2
2
D 10 moles of water, H O
5. We can compare the number of particles in
2
Examiner’s tip substances by just comparing the number of
Students need to know the molar mass and the mass moles of the substances. See Example 3.10.
of each substance, including glucose.
Substance Mass(g) = number of moles ×
molar mass EXAMPLE 3.10
1 mole C H O 6(12) + 12(1) + 6(16) = 180 How many times the number of atoms in 7 g of
6 12 6
3 moles 3 × [3(12) + 7(1) + 16 + 1] = 3 × nitrogen gas is larger than that in 7 g of iron? Chapter
C H OH 60 = 180
3 7 [Relative atomic mass: N, 14; Fe, 56]
4 moles C H 4 × [3(12) + 6(1)] = 4 × 42 = 168
3 6 Solution 3
6 moles C H 6 × [2(12) + 6(1)] = 6 × 30 = 180
2 6 We only need to compare the number of moles
10 moles H O 10 × [2(1) + 16] = 10 × 18 = 180 of both samples.
2
Answer: B The number of moles of nitrogen atoms
= mass ÷ molar mass
4. Substances with the same number of moles = 7 ÷ 14
have equal number of particles even though = 0.5 mol
the particles are different in size and mass. The number of moles of iron atoms
= mass ÷ molar mass
= 7 ÷ 56
28 g = 0.125 mol
12 g
0.5 mole of magnesium 0.5 mole of iron Number of moles of nitrogen atoms = 0.5 = 4
Number of moles of iron atoms 0.125
Figure 3.5 Both blocks of magnesium and iron have 0.5 x
6.022 × 10 atoms Therefore, 7 g of nitrogen gas has 4 times more
23
[Relative atomic mass: Mg, 24; Fe, 56] of atoms than that in 7 g of iron.
EXAMPLE 3.9
Number of moles and volume of gases
What is the mass of gold that has the same 1. The number of moles of a gas can also be
number of atoms as 4 g of oxygen? determined through its volume. This is not true
[Relative atomic mass: O, 16; Au, 197] of a solid or liquid substance.
Solution 2. All gases with the same volume under the
The number of oxygen atoms, O same pressure and temperature, have the same
= mass ÷ molar mass number of particles.
= 4 ÷ 16 = 0.25 mol 3. The volume of one mole of gas is known as
0.25 mole of gold has the same number of molar volume.
atoms as 0.25 mole of oxygen. So, the mass of • Molar volume of any gas is 22.4 dm
3
gold = number of moles × molar mass mol at STP or 24 dm mol at room
-1
3
-1
= 0.25 × 197 conditions.
= 49.25 g • STP refers to the standard temperature of
0ºC and the pressure of 1 atm.

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