How would you prepare 20ml of a 0.25 % dilution when provided with a 0.5% stock solution ?

Question

I DON'T HAVE A REALLY STRONG BACK GROUND IN CHEMISTRY AND I HAVE MY FIRST LAB NEXT WEEK COULD ANYONE GIVE ME LIKE A FORMULA TO ANSWER THIS .

Answer 1

V1C1 = V2C2

V1 = Initial Volume

C1 = Initial Concentration

V2 = Desired or Final Volume

C2 = Desired or Final Concentration

Plug the known values into the equation and solve.  You want 20 mL of 0.25% solution, and you are starting with 0.5% stock.  You need to know how much staock to use:

C1 = 0.5%

V2 = 20 mL

C2 = 0.25%

(V1)(0.5) = (20)(0.25)

V1 = (20)(0.25) / (0.5)

V1 = 10 mL