Calculate the concentration of the Cu2+(aq) solution in the 50.00 mL volumetric flask.

Question

A chemist needs to create a series of standard Cu2+(aq)Cu2+⁢(aq) solutions for an absorbance experiment. For the first standard, he uses a pipet to transfer 10.0010.00 mL of a 2.852.85 M Cu2+(aq)Cu2+⁢(aq) stock solution to a 250.0250.0 mL volumetric flask, and he adds enough water to dilute to the mark. He then uses a second pipet to transfer 10.0010.00 mL of the second solution to a 50.0050.00 mL volumetric flask, and he adds enough water to dilute to the mark. Calculate the concentration of the Cu2+(aq)Cu2+⁢(aq) solution in the 50.0050.00 mL volumetric flask.

Answer 1

Original [Cu²⁺] = 2.852 M

First dilution is 10.00 mls to 250.0 mls, which is a 25x dilution

Second dilution is 10.00 mls to 50.00 mls, which is a 5x dilution

Overall dilution is 25 x 5 = 125x

Final [Cu²⁺] = 2.852 M / 125 = 0.02282 M Cu²⁺

Done another way:

Original [Cu²⁺] = 2.852 M

Use V1M1 = V2M2

1^st dilution: (10.00 ml)(2.852 M) = (250.00 ml)(x M) and x = 0.1141 M Cu²⁺

2^nd dilution: (10.00 ml)(0.1141 M) = (50.00 ml)(x M) and x = 0.02282 M Cu²⁺