Introduction
The mole concept is a fundamental aspect of chemistry that helps in quantifying the amount of substance. It is crucial for understanding chemical reactions, stoichiometry, and various properties of substances. This study note will delve into the details of the mole concept, including its definition, calculations involving moles, and related concepts like molar mass and Avogadro's constant.
The Mole
Definition
The mole is one of the seven SI base units, used to measure the amount of substance. One mole is defined as the amount of substance that contains as many elementary entities (such as atoms, molecules, or ions) as there are atoms in 12 grams of carbon-12. This number is known as Avogadro's constant.
Avogadro's Constant
Avogadro's constant, denoted as $N_A$ or $L$, is the number of particles in one mole of a substance. Its value is approximately $6.022 \times 10^{23}$ mol$^{-1}$. For practical purposes in the IB syllabus, this number can be rounded to $6.02 \times 10^{23}$ mol$^{-1}$.
NoteAvogadro's constant is a fundamental constant in chemistry, providing the link between the macroscopic and microscopic worlds.
Calculation of Number of Particles
To calculate the number of particles $N$ in a sample, knowing the number of moles $n$, the following relationship is used:
$$ N = n \times N_A $$
Where:
- $N$ = number of particles
- $n$ = number of moles
- $N_A$ = Avogadro's constant ($6.02 \times 10^{23}$ mol$^{-1}$)
Example Calculation: If you have 2 moles of a substance, the number of particles in the substance can be calculated as:
$$ N = 2 , \text{mol} \times 6.02 \times 10^{23} , \text{mol}^{-1} = 1.204 \times 10^{24} , \text{particles} $$
Molar Mass
Definition
The molar mass $M$ of a substance is defined as the mass $m$ of the substance divided by the amount (in moles) of that substance. It is usually expressed in grams per mole (g/mol).
Calculation
The molar mass can be calculated using the formula:
$$ M = \frac{m}{n} $$
Where:
