Question

A reaction produces 74.10 g Ca(OH)2 after 56.08 g CaO is added to 36.04 g H2O. How should the difference in the masses of reactants and products be explained?

Answer 1

Cao +  H2O  ---->Ca(OH)2
Calculate   the  number  of  each   reactant  and  the  moles  of  the  product
that  is
moles = mass/molar mass
The  moles  of  CaO=  56.08g/  56.08g/mol(molar  mass  of  Cao)=  1mole
the  moles  of  water=  36.04 g/18  g/mol=  2.002moles
The   moles  of Ca (OH)2=74.10g/74.093g/mol= 1mole

 The  mass  of differences  of  reactant  and  product  can   be  therefore 
 explained  as 
 1  mole   of  Cao  reacted  completely   with   1  mole   H2O  to  produce  1 mole  of  Ca(OH)2. The  mass  of  water   was  in  excess  while  that  of  CaO  was  limited