Biochemistry

50 mg of the amino acid isoleucine (molecular weight of 131.2) has been dissolved in 50 ml water to produce a stock solution. What is the molarity of the stock solution? The assay mixture requires a final concentration of 200 µM isoleucine in 10 ml buffer. What volume of stock solution needs to be made up to 10 ml?

Any help would be appreiated

This isn't biochemistry.

Its chemistry based math using biological molecules as its base?

Biochem

Lol, take your homework elsewhere faggot

Well I do not take biochem but I love chemistry!
1) Find moles of amino acid isoleucine
   a. Convert 50mg=.05g
   b. # of moles isoleucine = given mass .05g /molecular weight 131.2g
   c. This is how many moles of amino acid isoleucine you have = 3.81097x10^-4 moles
2) Find Molarity
   a. M= number of moles Solute / Liters of Solution
   b. M= 3.81097x10^-4 moles / .5L water = 7.62195x10^-4

3) (Next part I'm not to sure but try this)
   a. Concentration (Or molarity) M=Moles of solute/liters of solution
   b. Convert 200micro M to .0002 M
   c. .0002 M = X / .1L Buffer
   d. Solve for x, which = .00002 = moles of solute
   e. Convert to grams .00002moles = Xg / 131.2g Isoleucine molecular weight = .002624g
   f. Since .002624g is needed
   g. I am kind of lost because it asks how much volume is needed, but you ask to fill it up 10mL so...the volume needed is 10mL but perhaps you were asking for the density?  That would be easy: D=m/V   .002624g / 10mL = 2.62x10^-4.

I hope this helps, and always double check your work.  I may have made a a mistake.! 

too bad it's grade 10 dimensional analysis, not chemistry