M1V1 = M2V2
Where M1 and M2 are the initial and final concentrations, respectively and V1 and V2 are the initial and final volumes", respectively. Given the dilution formula, we can plug in our known values to solve for M2. We expect the concentration to decrease since we will have the same number of moles in a larger volume of solution.
(4.00 M)(75.0 mL) = M2(500 mL).
We can use the volumes in mL instead of L as long as both volumes are in the same units. When we solve for M2 = 0.600 M KCl