A chemist makes a stock solution of potassium chromate by dissolving 97.1 grams of potassium chromate,

Question

in enough water to make 1.00 liter of solution. What volume of the stock solution must be diluted with water in order to prepare 200. mL of 0.200M solution?

Answer 1

Find concentration (M) of the original stock solution:

97.1 g K2CrO4 x 1 mol/194 g = 0.00515 moles

0.5005 moles/1.00 L = 0.5005 M

Next, use V1M1 = V2M2 to find the volume of this stock needed to make 200. ml of 0.200 M

V1 = initial volume = ?

M2 = initial molarity = 0.5005 M

V2 = final volume = 200. ml

M2 = final molarity = 0.200 M

(V1)(0.5005 M) = (200. ml)(0.200 M)

V1 = 79.9 mls of stock needed (to 3 sig. figs.)