Chemistry MOLARITY Help?!?!

You make two dilutions. You take 102.3 mL of the stock solution and dilute to 500.0 mL to make Solution #1. You then add 57.25 mL of Solution #1 to 32.11 mL of water to make Solution #2.

What is the concentration of the Solution #1 in terms of molarity?

The concentration of stock solution is 7.977×10-5 M.

First convert the ml to L to get .1023L

Then find the moles of the initial solution (remember that Molarity is just moles per liter)
like this .1023L x 7.977x10^-5mol/1L = 8.16x10^-6mol.
Use these moles to find the concentration of solution #1 (again remember to convert ml to L to keep things simple)
8.16x10^-6mol/.500L = 1.632x10^-5Molar

then find the # of moles in 57.25ml sample of solution #1
.05725L x 1.632x10^-5mol/L = 9.34x10^-7mol in sample of solution #1

Then find the concentration of solution #2. Since you are adding to 32.11ml to the sample of 57.25ml remember to add them together to give the total volume of the solution #2.

Then since you know how many moles were in the sample (9.34x10^-7mol), just find the concentration.

9.34x10^-7mol/.08936L = 1.045x10^-5M (concentration of solution #2)

but if you only need to know the concentration of solution #1 then you got it at the very beginning 1.632x10^-5Molar