Concentration and molarity?

Question

How many milliliters of a 135 mL solution of 0.8 M K3PO4 must be used to make 56 mL of a solution that has a concentration of 0.35 M K+?

Answer 1

use n = cV in the form c1V1 = c2V2
c1 = 0.8 M
c2 = 0.35 M
V2 = 56 mL
(the 135 mL value is irrelevant)

rearranging, V1 = c2/c1 * V2 = 0.35/0.8 * 56 = 24.5 mL
this is assuming the solution is being diluted with water (31.5 mL of water are required).

Answer 2

Yeah, I second vorenhutz method.....

c1v1=c2v2
(0.8M) v1= (0.35M) (56mL)
v1=(0.35M) (56mL) / 0.8M
v1= 24.5mL

To achieve 56mL; 56mL-24.5mL=31.5mL
which means that 31.5mL of distilled water added to achieved the stated concentration.... ;P