MOLAR MASS

The mass of one mole of a substance is called molar mass. The molar mass of:

 (i) an element has mass equal to relative atomic mass /RAM(in grams)of the element e.g.

 Molar mass of carbon(C)= relative atomic mass  = 12.0g

   6.023 x10 ²³ particles  of carbon  = 1 mole  =12.0 g

 Molar mass of sodium(Na) = relative atomic mass  = 23.0g

6.023 x10 ²³ particles  of sodium  = 1 mole  =23.0 g

 Molar mass of Iron (Fe)  =  relative atomic mass  = 56.0g

6.023 x10 ²³ particles  of iron  = 1 mole  =56.0 g

(ii)a molecule has mass equal to relative molecular mass /RMM (in grams)of the molecule. Relative molecular mass  is the sum of the relative atomic masses of the elements making the molecule. e.g.

Molar mass Oxygen molecule(O₂) =relative molecular mass =(16.0x 2)g =32.0g

6.023 x10 ²³ particles  of Oxygen molecule = 1 mole  = 32.0 g

Molar mass chlorine molecule(Cl₂) =relative molecular mass =(35.5x 2)g =71.0g

6.023 x10 ²³ particles  of chlorine molecule = 1 mole  = 71.0 g

Molar mass Nitrogen molecule(N₂) =relative molecular mass =(14.0x 2)g =28.0g

6.023 x10 ²³ particles  of Nitrogen molecule = 1 mole  = 28.0 g

(ii)a compound has mass equal to relative formular mass /RFM (in grams)of the molecule. Relative formular mass  is the sum of the relative atomic masses of the elements making the compound. e.g.

(i)Molar mass Water(H₂O) = relative formular mass =[(1.0 x 2 ) + 16.0]g =18.0g

6.023 x10 ²³ particles  of Water molecule = 1 mole  = 18.0 g

6.023 x10 ²³ particles  of Water molecule has:

          - 2 x 6.023 x10 ²³ particles  of Hydrogen atoms

          -1 x 6.023 x10 ²³ particles  of Oxygen atoms

(ii)Molar mass sulphuric(VI)acid(H₂SO₄) = relative formular mass

 =[(1.0 x 2 ) + 32.0 + (16.0 x 4)]g =98.0g

6.023 x10 ²³ particles of sulphuric(VI)acid(H₂SO₄) = 1 mole = 98.0g

6.023 x10 ²³ particles of sulphuric(VI)acid(H₂SO₄) has:

          - 2 x 6.023 x10 ²³ particles  of Hydrogen atoms

           -1 x 6.023 x10 ²³ particles  of Sulphur atoms

           -4 x 6.023 x10 ²³ particles  of Oxygen atoms

(iii)Molar mass sodium carbonate(IV)(Na₂CO₃) = relative formular mass

 =[(23.0 x 2 ) + 12.0 + (16.0 x 3)]g =106.0g

6.023 x10 ²³ particles of sodium carbonate(IV)(Na₂CO₃) = 1 mole = 106.0g

6.023 x10 ²³ particles of sodium carbonate(IV)(Na₂CO₃) has:

          - 2 x 6.023 x10 ²³ particles  of Sodium atoms

           -1 x 6.023 x10 ²³ particles  of Carbon atoms

           -3 x 6.023 x10 ²³ particles  of Oxygen atoms

(iv)Molar mass Calcium carbonate(IV)(CaCO₃) = relative formular mass

 =[(40.0+ 12.0 + (16.0 x 3)]g =100.0g.

 6.023 x10 ²³ particles of Calcium carbonate(IV)(CaCO₃) = 1 mole = 100.0g

6.023 x10 ²³ particles of Calcium carbonate(IV)(CaCO₃) has:

          - 1 x 6.023 x10 ²³ particles  of Calcium atoms

           -1 x 6.023 x10 ²³ particles  of Carbon atoms

           -3 x 6.023 x10 ²³ particles  of Oxygen atoms

 (v)Molar mass Water(H₂O) = relative formular mass

             =[(2 x 1.0 )+ 16.0 ]g =18.0g

          6.023 x10 ²³ particles of Water(H₂O) = 1 mole = 18.0g

          6.023 x10 ²³ particles of Water(H₂O) has:

          - 2 x 6.023 x10 ²³ particles  of Hydrogen atoms

          -2 x 6.023 x10 ²³ particles  of Oxygen atoms