chem
posted by mel .
A standard solution is prepared for the analysis of fluoxymesterone (C20H29FO3), an anabolic steroid. A stock solution is first prepared by dissolving 13.0 mg of fluoxymesterone in enough water to give a total volume of 500.0 mL. A 100.0 µL aliquot (portion) of this solution is diluted to a final volume of 100.0 mL. Calculate the concentration of the final solution in terms of molarity.

To make things easier (on me to type) let's call fluoxymesterone just FLM.
13.0 x 10^3 g FLM/500 mL = xx g FLM/mL.
That is the stock solution.
It is diluted 100.0 microliters to 100.0 mL. So the new solution is
xx g FLM/mL x (100.0 x 10^3 mL/100.0 mL) = yy g FLM/mL.
To find the molarity just multiply
yy g FLM/mL x 1000 mL = zz g FLM/L.
zz g FLM/molar mass FLM = mols and this is molarity since this is # mols in 1 L.
Check my thinking. Check my work. Watch the units. Make sure I made the conversions properly.