What volume of a 3.70 M KI stock solution would you use to make 0.400 L of a 1.25 M KI solution?

To determine the volume of the 3.70 M KI stock solution required to make a 0.400 L of 1.25 M KI solution, you can use the formula:

C1V1 = C2V2

Where:
C1 = concentration of the stock solution (3.70 M)
V1 = volume of the stock solution (unknown)
C2 = concentration of the desired solution (1.25 M)
V2 = desired volume of the solution (0.400 L)

Rearranging the formula, we get:

V1 = (C2 * V2) / C1

Substituting the given values, we can calculate the volume of the stock solution:

V1 = (1.25 M * 0.400 L) / 3.70 M
V1 = (0.5 L) / 3.70
V1 ≈ 0.135 L

Therefore, you would need approximately 0.135 liters (135 mL) of the 3.70 M KI stock solution to make 0.400 L of a 1.25 M KI solution.