You need to find the concentration of copper in a dark blue solution of CuS04. T

Question

You need to find the concentration of copper in a dark blue solution of CuS04. The original solution is too concentrated to test directly using UV-Vis absorption. To make an appropriate sample, you pipette 10.00 ml of the original solution into a 250.00 mL volumetric flask and fill the remaining volume with Dl water. You then pipette 2.00 ml of the newly made solution into a 25.00 mL volumetric flask and fill the remaining volume with Dl water. When you test a 5 ml sample of the most dilute solution, you find the copper concentration to be 0.00387M. What is the molarity of copper in the original solution?

Explanation / Answer

Let M1 be the molarity of Copper in original solution.

Dilution-1: 10.00 mL of M1 molar Copper solution diluted to 250.00 mL.

Initially we have, Molarity M1, Volume V1 = 10.00 mL

Finally we have, Molarity M2 and V2 = 250.00 mL

Molarity equation for dilution says,

M1 x V1 = M2 x V2

M1 x 10.00 = M2 x 250.00

M2 x 250.00 = 10.00 x M1

M2 = (10.00/250.00) x M1

M2 = 1/25 x M1

M2 = 0.04 M1

Dilution-2: 2.00 mL of M2 = 0.04M1 molar Copper solution diluted to 25.00 mL.

For dilution-2 we have

Initially, Molarity M3 = M2 = 0.04 M1 and V3 = 2.00 mL

Finally, Molarity M4 = 0.00387 and V4 = 25.00 mL

Molarity equation holds again,

M3 x V3 = M4 x V4

0.04 M1 x 2.00 = 0.00378 x 25.00

M1 x 0.08 = 0.0945

M1 = 0.0945/0.08

M1 = 1.18125

In original solution molarity of Copper was 1.18125 M.

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