Stuck on chemistry problem due today

Question

You are trying to determine the concentration of a stock solution of hydrochloric acid. You have 450.80 mL of 0.86 M dilute solution that was prepared with 25.50 of stock solution

Answer 1

Here is how you do this one, first you use of the fact that molarity is mol/liter. So converting ml to Liters is 450.08 mL = .4508 L and 25.50 ml = 0.0255 L we then solve for the first of two unknowns. The first unknown is the amount of mol in the dilute HCl .xmol/.4508 = .86 M solving for xmol we get .86*.4508 = .38 mol = xmol. We then take the found xmol (.38 mol) and plug it into the concentration formula. We get .38 mol/0.0255L = 15.2 M stock solution as your final answer. I hope this helps!