Avogadro's Number

Avogadro's Number (N_A​) represents the number of molecules, atoms, or particles in one mole of any substance. The unit of Avogadro's number is mol⁻¹, meaning it defines the number of particles per mole. This constant helps relate the macroscopic quantity of a substance (in moles) to the microscopic number of individual particles.

A mole is a unit that represents 6.022×10²³ particles (atoms, molecules, or ions), just like a dozen represents 12 items. For example, one mole of water, which weighs 18 g, contains 6.022×10²³ molecules of water.

To find the number of molecules in 66 g of CO₂​, follow these steps:

1. Calculate the number of moles of CO₂​:

The molecular mass of CO₂ is 44 g/mol.
Number of moles ($n$) = `"Mass of CO2 in grams"/"Molecular mass of CO2"`=`"66"/"44"`

n=`"66"/"44"`=1.5 mol.

2. Find the number of molecules in 1.5 moles of CO₂_​:
1 mole of CO₂​ contains 6.022×10²³ molecules.
So, 1.5 moles of CO₂_​ = 1.5×6.022×10²³

= 9.033×10²³ molecules.

Thus, 66 g of CO₂​ contains 9.033×10²³ molecules.

One mole (Avogadro number)