Question

Ho w
much 
water
 would 
you 
need 
to
 add
 to

500
mL
 of 
a 
0.3
M
 calcium
 nitrate 
solution
 to 
make
the
 solution
 0.1
M?

A.

1.0
L
B.

0.50
L
C.

1.5
L
D.

0.25
L
E.

3.0
L

The answer is A but I cannot figure it out.

Answer 1

Use the dilution formula.
mL1 x M1 = mL2 x M2
500 mL x 0.3M = mL2 x 0.1M
mL2 = you do it.
mL2 is the final volume of the solution. You want to know how much water to add. Assuming volumes are additive, you would need to add the difference between mL2 and 500 mL.

An easier way to do this is to note you have 0.3M and you want to make 0.1M. So you want to dilute it a factor of 3 times. 3*500 = 1500 final volume. So you add 1500-500 = ?