Help needed ASAP!!

Question

Can you provide step my step directions/work on how to do this? I'm confused

You wish to make a 100 microliter enzyme reaction cocktail that contains 200 mM MgCl2. The concentration of your MgCl2 stock solution is 2.5 mM. How much 2.5 mM MgCl2 would you have to add to you cocktail to bring it to a final concentration of 200 micromoles MgCl2?

Answer 1

You can look at this as a V1M1 = V2M2 problem

Your problem is that the stock solution is 2.5 mM and you are trying to dilute it to make a solution that is 200 mM. Do you see why this is IMPOSSIBLE?

In the last sentence it asks how to bring it to a final concentration of 200 micromoles of MgCl2. This is NOT a concentration, as it doesn't contain a volume? Is that supposed to 200 micromolar? If that's the case, then you can use V1M1 = V2M2

(x ml)(2.5 mM) = (0.1 ml)(0.2 mM)

x = 0.008 ml

x = 8 microliters of the stock would have to be added to 92 ul of cocktail to end up with 200 uM MgCl2 (0.2 mM MgCl2)