The formula for potassium chlorate is:   2KClO₃  →  2KCl  +  3O₂
If moles =  mass ÷ molar mass Â
then moles of KClO₃  =  25 g  ÷  [( 39 × 1 ) + ( 35.5 × 1) + ( 16 × 3)] g/mol
          Â
                  = 25 g  ÷ ( 122.5 g ) g/mol
                  =  0.2041 mol
Now the mole ratio of  KClO₃   :  O₂   is   2  :  3
∴  if moles of KClO₃  = 0.2041 mol
  then moles of O₂   =  ( 0.2041 mol ÷ 2 ) × 3
     Â
                 = 0.3061 mol
Now since mass = moles × molar mass
∴ the mass of oxygen produced  =  0.3061 mol  × ( 16 × 2) g/mol
                          =  9.796 g
∴ the grams of oxygen gas produced when 25 grams of potassium chlorate is decomposed is ~ 9.80 g.
