Mole and Molarity

 

Mole and Molarity

1. Mole (mol)

A mole is a fundamental unit in chemistry used to measure the amount of substance. It is defined as:

1 mole of any substance contains Avogadro’s number ($6.022 \times 10^{23}$) of particles (atoms, molecules, or ions).

Formula for Moles:

$$\text{Moles} = \frac{\text{Given mass (g)}}{\text{Molar mass (g/mol)}}$$

Example:

If you have 18 g of water ($H_2O$), its molar mass is:

$$\text{Molar mass of } H_2O = (2 \times 1) + 16 = 18 \text{ g/mol}$$
$$\text{Moles of } H_2O = \frac{18}{18} = 1 \text{ mol}$$

---

2. Molarity (M)

Molarity is the concentration of a solution, representing the number of moles of solute per liter of solution. It is expressed as:

$$\text{Molarity (M)} = \frac{\text{Moles of solute}}{\text{Volume of solution in liters (L)}}$$

Example:

If 0.5 moles of NaCl is dissolved in 1 liter of water, then:

$$M = \frac{0.5}{1} = 0.5 \text{ M}$$

Key Differences Between Mole and Molarity:

Property	Mole	Molarity
Definition	Amount of substance	Concentration of solution
Unit	mol	mol/L (M)
Formula	$\frac{\text{Mass}}{\text{Molar Mass}}$	$\frac{\text{Moles of solute}}{\text{Liters of solution}}$