A mole (mol) of a substance is 6.02 × 10²³ representative particles of that substance. The representative particles can be atoms (element), molecules (covalent compounds), or formula units (ionic compound).
Example 1: moles to representative particle
How many molecules are there in 4.0 moles of carbon dioxide CO2?
To answer this question, remember that,
1 mole = 6.02 × 10²³ particles
4.0 moles CO2 x 6.02 × 10²³ molecules of CO2 = 2.41 × 10²4 molecules of CO2
1 mole of CO2
Example 2: moles to representative particle
Aluminum (Al), a metal with a high strength-to-weight ratio and a high resistance to corrosion, is often used for structures such as high-quality bicycle frames. Compute both the number of moles of atoms and the number of atoms in a 10.0-g sample of aluminum.
Solution:
atomic mass of Aluminum is 26.98
1 mole of Al = 26.98 g of Al
10.0 g of Al x 1 mol of Al = 0.37 mol of Al
26.98 g of Al
Next, we will convert from moles of atoms to the number of atoms, using the equivalence statement
6.022 × 10²³ Al atoms = 1 mol of Al
0.37 mol of Al x 6.02 × 10²³ Al atoms = 2.23 × 10²³ Al atoms
1 mol of Al
Example 3: moles to mass
How many grams are 10.78 moles of Calcium (Ca)?
To answer this question, remember that,
atomic mass of Ca is 40.08 therefore, 1 mole of Ca = 40.08 g of Ca
10.78 moles of Ca x 40.08 g of Ca = 432.06 g of Ca
1 mole of Ca
Example 4: mass to representative particle
How many atoms are in a 3.5 g sample of sodium (Na)?
To answer this question, remember that,
1 mole = 6.02 × 10²³ particles
atomic mass of Na is 23 therefore, 1 mole of Na = 22.99 g of Na
3.5 g of Na x 1 mole of Na = 0.15 mole of Na
22.99 g of Na
0.15 mol of Na x 6.02 × 10²³ atoms of Na = 0.903 × 10²³ atoms of Na
1 mol of Na
