Edexcel iGCSE Chemistry -1.27 Mole- Study Notes- New Syllabus
Edexcel iGCSE Chemistry -1.27 Mole- Study Notes- New syllabus
Edexcel iGCSE Chemistry -1.27 Mole- Study Notes -Edexcel iGCSE Chemistry – per latest Syllabus.
Key Concepts:
1.27 know that the mole (mol) is the unit for the amount of a substance
1.27 The Mole (mol) – The Unit for Amount of Substance
The mole (mol) is the unit used to measure the amount of a substance.
Chemists use the mole to count particles such as atoms, molecules or ions.
Definition of a Mole
One mole of any substance contains:
\( 6.02 \times 10^{23} \) particles
This number is called Avogadro’s number.
Why the Mole Is Needed
Atoms and molecules are extremely small.
Instead of counting individual particles, we count them in moles.
This allows us to link:
• Mass of a substance
• Number of particles
• Chemical equations
Key GCSE Relationships
The mole connects mass and relative formula mass:
\( \text{number of moles} = \dfrac{\text{mass (g)}}{M_r} \)
Units:
mass → grams (g) amount → moles (mol)
What 1 Mole Means in Practice
| Substance | 1 mole contains |
|---|---|
| Carbon atoms | \( 6.02 \times 10^{23} \) carbon atoms |
| Water molecules | \( 6.02 \times 10^{23} \) water molecules |
| Sodium ions | \( 6.02 \times 10^{23} \) sodium ions |
Important Exam Point
The mole is a unit for amount of substance, not mass.
Different substances have different masses for 1 mole because they have different Mr values.
Example 1 (Conceptual):
Why does 1 mole of oxygen gas contain more mass than 1 mole of hydrogen gas?
▶️ Answer/Explanation
Both contain the same number of molecules.
However, oxygen molecules have a larger relative molecular mass than hydrogen molecules.
Therefore, 1 mole of oxygen has greater mass.
Example 2 (Numerical):
How many moles are present in 18 g of water? (Mr of water = 18)
▶️ Answer/Explanation
\( \text{moles} = \dfrac{18}{18} \)
\( = 1 \text{ mol} \)
Example 3 (Hard):
Explain fully what is meant by the statement: “24 g of magnesium is 1 mole of magnesium.”
▶️ Answer/Explanation
The relative atomic mass of magnesium is 24.
One mole of any element has a mass equal to its relative atomic mass in grams.
So 1 mole of magnesium has a mass of 24 g.
This contains \( 6.02 \times 10^{23} \) magnesium atoms.
Therefore, 24 g of magnesium represents 1 mole.