Answer:
50 mL
Step-by-step explanation:
To prepare a solution, we need to put the one we have in some more solvent. To know the concentration and the volume, we can use the equation of dilution:
C1.V1 = C2.V2
Where C1 is the initial concentration, V1 is the volume of this solution, C2 is the concentration of the new solution, and V2 is the volume of this solution.
How we have both concentrations in w/v or weight/volume, we need only put them on the same basis, so:
C1 = 0.04
C2 = 0.002
The final volume is 1L, or 1,000 mL (the units should be the same for the final and initial).
C1.V1 = C2. V2
0.04. V1 = 0.002 . 1,000
V1 = 50 mL
So, it's necessary 50 mL of the initial solution.