Prepare ~ 8.75 * 10-4 M CrO4 solution from the ~1.25 * 10-3 M K2CrO4 stock solution. Record the exact molarity of the stock solution. Calculate the required amount of stock solution to make 10.00 mL of dilute solution. Adjust this value as necessary (ratio) based on the volumetric flask available.

7 mL

Explanation:

To prepare a solution by dilution of another one, we can use the equation:

C1V1 = C2V2

where C is the concentration, V is the volume, 1 is the initial solution, and 2 the final solution. V represents the total volume. K₂CrO₄ dissolver by:

K₂CrO₄ → 2K⁺ + CrO₄⁻²

So, 1 mol of K₂CrO₄ results in 1 mol of CrO₄⁻², the in a solution of 8.75x10⁻⁴M of CrO₄⁻², it will be 8.75x10⁻⁴M of K₂CrO₄, so the volume of the stock solution will be:

1.25x10⁻³xV1 = 8.75x10⁻⁴x10

V1 = (8.75x10⁻³) / (1.25x10⁻³)

V1 = 7 mL