Which one is the correct way to practice?

a). Dissolving 1000mg of Lead nitrate into 1L water;

==> Concentration = 1000mg/L as a lead ion.

b). Follow the formula: Molecular weight of lead nitrate / Atomic weight of lead.

( Molecular weight of lead nitrate=331.2g/mole; Atomic weight of lead=207.2)

==> 331.2 /207.2 =1.598 g, then dissolve it in 1L of water. As a result, it will get 1000mg/L.

( 1 gram weight is lead and 0.598g is other elemental weight.)

How about Cu from Cupper Sulfate Pentahydrated?

a). Dissolving 1000mg of Copper Sulfate Pentahydrated into 1L water;

==> Concentration = 1000mg/L as a lead ion.

b). Follow the formula: Molecular weight of lead nitrate / Atomic weight of lead.

==> 249.68 /64= 3.9 g, then dissolve it in 1L of water.

++ As a result, will it get 1000mg/L??