Chem Help!! Please!?

Question

(a) How many milliliters of a stock solution of 15.0 M HNO3 would you have to use to prepare 0.500 L of 0.200 M HNO3?
________ mL
(b) If you dilute 15.0 mL of the stock solution to a final volume of 1.00 L, what will be the concentration of the diluted solution?
_______ M

Answer 1

(a) 500 mL of 0.200 M contains 0.1 moles.
The solution 15.0 M means 15 moles in 1000 mL
1000 : 15 = x : 0.1
x=6.67 mL

(b)15 mL of solution 15.0 M contain
1000 mL: 15 mole = 15 mL : x mole
x= 0.225
M= mole/L = 0.225/1=0.225 M