Question

What mass of oxygen would be produced upon thermal decomposition of 25 g of potassium chlorate (kclo3)? the molecular weight (mw) of potassium chlorate is 122.5 g/mol?

Answer 1

The formula for potassium chlorate is:    2KClO₃   →   2KCl   +   3O₂

If moles =  mass ÷ molar mass  

then moles of KClO₃   =  25 g  ÷  [( 39 × 1 ) + ( 35.5 × 1) + ( 16 × 3)] g/mol
                     
                                   = 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
          
                                  = 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.