making a 1mg/ml solution

Question

I have a stock powder that says it is 278.31 g/mol.  I need to make a 50 ml solution that is 1mg/ml.  How much powder do I need to add to the 50ml flask?

Answer 1

1 mg/ml x 50 ml = 50 mg

You need to weigh out 50 mg, add it to a 50 ml volumetric flask, and bring to a final volume of 50 ml.

The molar mass (278.31 g/mol) does not come into play for this calculation.  If you want to know the molarity of the prepared solution, that would be 50 mg x 1 mmol/278.31 mg/0.05 L = 3.6 mmol/L = 3.6 mM (3.6x10^-3 M)