A solution of 10 M NaOH was used to prepare 2 L of 0.5 M NaOH. How many mL of the original NaOH solution are needed?

a. 10 mL

b. 100 mL

c. 1000 mL

d. 200 mL

e. 2000 mL

The equation to solve problem is (M1) (V1) = (M2) (V2)

M1 = 10M, V1 = original NaOH solution, M2 = 0.5 M, V2 = 2L

First, the answer needs to be in ml., so convert 2L to ml = 2000ml

(10M) (V1) = (0.5M) (2000ml)

(10M) (V1) = 1000 M/ml

V1 = 1000M/ml / 10M, the Mmoles cancel out leaving just ml.

V1 = 100ml, which is the original NaOH solution needed.