If the absorbance of a solution of copper(II) ion decreases by 26.00% upon dilution, what volume of water was added to 20.0 mL of a 1.20 M solution of Cu2+(aq)?

Answer 1

Assuming that absorbtion is linear with concentration, we have....

V1 = initial volume = 20.0 ml

M1 = initial molarity = 1.20 M

V2 = final volume = ?

M2 = final molarity = 74% of 1.20 M = 0.888 M (since the molarity decreased by 26%, that leaves 74%)

V1M1 = V2M2

(20.0 ml)(1.20 M) = (V2)(0.888 M)

V2 = 27.0 ml ... Note: this is the final volume, not the volume of water added.

Volume of water added to original solution = 27.0 ml - 20.0 ml = 7.0 mls added