[elli]

How many grams of copper sulfate pentahydrate is required to have a 50 mg/L concentration of copper?

[sjb]

This will depend on how much stock solution you need. Any formulas you know that might help?

[billnotgatez]

Some data from WIKI that might aid in the discussion

Copper(II) sulfate
Chemical formula
CuSO4 (anhydrous)
CuSO4·5H2O (pentahydrate)
Molar mass
159.60 g/mol (anhydrous)
249.685 g/mol (pentahydrate)

Copper
Standard atomic weight
63.546
Atomic number 
29

Sulfurl
Standard atomic weight conventional
32.06
Atomic number
16

Oxygen
Standard atomic weight conventional
15.999
Atomic number
8