Lecture 3 – Molar Formulae & Calculations

Mathematics of Moles:

Formula # 1:

i.                    For Elements:

ii.                  For Compounds:

Example:

a.     Calculate the number of moles in 110 g of CO₂.

b.     Calculate the number of moles in 128 g of Cu.

c.      Calculate the mass in grams for 4.5 moles of CH₄.

Formula # 2:

i.                    For Elements:

 ii.                  For Compounds:

Avogadro’s Number = 6.02 x 10²³ = is a constant

Example:

a.     Calculate the number of atoms in 2 moles of Ne.

       

b.     Calculate the number of atoms in 1.5 moles of Fe.

          

c.      Calculate the number of atoms in 3.5 moles of CO₂.

    

Formula # 3:

i.                    For Elements:

ii.                  For Compounds:

Avogadro’s Number = 6.02 x 10²³ = is a constant

Formula # 4:

i.                    For Elements:

ii.                  For Compounds:

Molar Gas Volume = M.G.V = 24dm³

Example:

a.     Calculate the volume occupied by 2 moles of NH₃.

Formula # 5:

i.                    For Elements:

ii.                  For Compounds:

Molar Gas Volume = M.G.V = 24dm³

Example:

a.     Calculate the volume occupied by 22g of CO₂.

b.     Calculate the volume occupied by 72g of Ne.