CIE AS/A Level Chemistry 2.2 The mole and the Avogadro constant Study Notes- 2025-2027 Syllabus
CIE AS/A Level Chemistry 2.2 The mole and the Avogadro constant Study Notes – New Syllabus
CIE AS/A Level Chemistry 2.2 The mole and the Avogadro constant Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on AS/A Level Chemistry latest syllabus with Candidates should be able to:
- define and use the term mole in terms of the Avogadro constant
The Mole and the Avogadro Constant
The mole is the standard SI unit for amount of substance. It links the microscopic world of atoms and molecules to measurable amounts in the laboratory.
\( \text{1 mole} = \text{the amount of substance containing } N_\mathrm{A} \text{ particles} \)
\( N_\mathrm{A} = 6.022\times10^{23}\,\mathrm{mol^{-1}} \) (Avogadro constant)
Definition of a Mole
A mole is the amount of substance containing exactly \( 6.022\times10^{23} \) particles (atoms, molecules, ions, electrons, etc.).
- This number is the Avogadro constant, \( N_\mathrm{A} \).
- 1 mole of any substance contains the same number of particles, even if the masses differ.
Using the Mole
Number of particles \( = n \times N_\mathrm{A} \)
Amount of substance \( n = \dfrac{\text{number of particles}}{N_\mathrm{A}} \)
Example
Define one mole in terms of the Avogadro constant.
▶️ Answer / Explanation
One mole is the amount of substance containing \( 6.022\times10^{23} \) particles (the Avogadro constant).
Example
How many molecules are there in \( 0.25\,\mathrm{mol} \) of \( \mathrm{CO_2} \)?
▶️ Answer / Explanation
Number of molecules \( = n \times N_\mathrm{A} \)
\( = 0.25 \times 6.022\times10^{23} \)
\( = 1.506\times10^{23} \) molecules
Example
A sample contains \( 3.01\times10^{22} \) atoms of magnesium. Calculate the amount of magnesium in moles.
▶️ Answer / Explanation
\( n = \dfrac{\text{number of particles}}{N_\mathrm{A}} \)
\( n = \dfrac{3.01\times10^{22}}{6.022\times10^{23}} \)
\( n = 0.0500\,\mathrm{mol} \)
The sample contains \( 0.0500\,\mathrm{mol} \) of magnesium.