Question

If 100 mL of a 3 M solution of sodium hydroxide is diluted to a total volume of 600 mL with distilled water, what will the final concentration of sodium hydroxide be?

Answer 1

You can do it one of two ways.
1. Use the dilution formula.
mL x M = mL x M

2. Use reason. You know that it must be more dilute going from 100 mL to 600 mL. So the molarity is
3M x (100/600) = ??

3. A third way, and one some students like is to do it with moles.
How many moles do you have in the original solution? You have M x L = 3 M x 0.1L = 0.3 mole.
You must have 0.3 mole in the diluted solution, of course, but the final volume is 600 mL or 0.6 L.
M = moles/L = 0.3/0.6 = ??

Answer 2

0.5M