Number of Mole of Atoms and Number of Mole of Molecules

  1. All molecules contain more than one atom.
  2. For example, in a carbon dioxide molecule (CO2), there are 3 atoms - 1 carbon atom and 2 oxygen atoms.
  3. Therefore, in 5 carbon dioxide molecules, there will be 15 atoms  - 5 carbon atom and 10 oxygen atoms.
  4. Similarly,  in 1 mole carbon dioxide molecules, there will be 3 mole atoms  - 1 mole carbon atoms and 2 mole oxygen atoms, and in 3 mole carbon dioxide molecules, there will be 9 mole atoms  - 3 mole carbon atoms and 6 mole oxygen atoms, so on and so forth.

Example:
  1. How many hydrogen molecules can be made with 20 mol of hydrogen atoms?
  2. How many hydrogen atoms are there in 20 mol of hydrogen molecules?
Answer:
a. 
Each hydrogen molecules (H2) consist of 2 hydrogen atoms.
Therefore, 20 mol of hydrogen atoms can make 10 mole of hydrogen molecules.

b. Number of mole of hydrogen atoms in 20 mole of hydrogen molecules

= 2 x 20 mole = 40 mole.

Example:
  1. Find the number of carbon atom in 0.75 mol of carbon dioxide.
  2. Find the number of oxygen atom in 0.75 mol of carbon dioxide.
Answer:
a. 
Each carbon dioxide molecules (CO2) consist of 1 carbon atom and 2 oxygen molecules.
Therefore, 0.75 mole of carbon dioxide contain 0.75 mole carbon atoms.

b.

Number of mole of oxygen atoms in 0.75 mole of carbon dioxide
= 2 x 0.75 mole = 1.50 moles.