A chemist needs to create a series of standard Cu^2+(aq) solutions for an absorb

Question

A chemist needs to create a series of standard Cu^2+(aq) solutions for an absorbance experiment. For the first standard, he uses a pipet to transfer 10.00 mL of a 2.36 M Cu^2+(aq) stock solution to a 250.0 mL volumetric flask and adds enough water to dilute to the mark. He then uses a second pipet to transfer 20.00 mL of the second solution to a 50.00 mL volumetric flask and adds enough water to dilute to the mark. Calculate the concentration of the Cu^2+(aq) solution in the 50.00 mL volumetric flask.

Explanation / Answer

for 1st dilution,
Since during dilution number of moles doesn't change

number of moles before dilution = number of moles after dilution
Ci*Vi = Cf*Vf

since number of moles = concentration (C) * volume (V)

use:
Ci*Vi = Cf*Vf
2.36 * 10 = Cf * 250
Cf = 0.0944 M

for 2nd dilution:
Ci = 0.0944 M
Vi = 20 mL
Vf = 50 mL
Cf= ?

use:
Ci*Vi = Cf*Vf
0.0944* 20 = Cf * 50
Cf = 0.038 M
Answer: 0.038 M

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