Deferentiate mole and gram mole.

Mole and gram mole.

   Mole is a number equal to 6.02×10^23 particals (atoms, molecules or ions ) also called avogadro number. While gram mole is a quantity equal to atomic weight or molecular weight in grams (gram atom or gram molecule). Since 6.02×10^23 particals weigh aqual to atomic weight or molecular weight in grams therefore mole and gram mole are used interchangeably.
eg one mole of water means 6.02×10^23 water molecules. And one gram mole of water means 18 gram water. And 18 g water contains  6.02×10^23 water molecules.

    Atomic/ molecular weight :

The weight of one atom/molecule of a substance is called atomic weight or molecular weight. Its unit is amu or unit less.

       1. Hydrogen. 

           6.02×10^23 H atoms =1.008g
            1                 H atom   = x

            X= 1.008×1/6.02×10^23 =1.67×20^-24 g =1amu

   So the weight of one atom of hydrogen (atomic weight of H) is 1 amu

       2. Oxygen. 

          6.02×10^23 oxygen atoms = 15.9 g
             1            oxygen atom = X

        X =1×15.9/ 6.02×10^23 = 2.64×10^-23 g = 15.9 amu

      (1.66×10^-24 g = 1amu
         2.64×10^-23 g = X
X=2.62×10^-23×1/ 1.66×10^-24 =15.9 g)
        
      So (the weight of one atom) atomic weight of oxygen is 15.9 amu.

       3. Water. 

      6.02×10^23 water molecules = 18 g
            1               water molecule = X g

   X =1×18/  6.02×10^23 = 2.99×10^-23 g
                            ÷1.66×10^-24 =18 amu

  So 18 amu is the weight of one molecule of water ( molecular weight of water.

       pH and gram mole

       For water [H*] = 10^-7 mole/ L or g mole/ L at 25°C
     Since 1 mole of H* = 1 g of H*
     Therefore 10^-7 mole of H* = 10^-7 g H*
   So one L (1kg)of water contains 10^-7 g if H*

    Also for water [OH-]= 10^-7 g mole/ L
    Since one g mole of OH- =17 g
    Therefore 10^-7 g mole of OH- 17×10^-7 g.
So one L (1kg) of watet contains 17×10^-7 g of OH-.