I was already able to solve the concentration level it is asking in the first pa

Question

I was already able to solve the concentration level it is asking in the first part of the question. How can I solve the second part of the question for the mass percent of copper in the second brass washer?

If a second brass washer of 0.6003 grams had been dissolved in nitric acid, diluted to 50.00 mL and then its absorbance measured at 0.450, what would be the concentration of Cu(NO3)2 in the solution? What would be the mass percent of copper in the second brass washer? Use the equation of the line as y=3.129x+0.0055.

Explanation / Answer

Putting the value of absorbance in the given calibration equation:

y = 3.129x + 0.0055

0.450 = 3.129x + 0.0055

So, x = 0.142 units

I assume that the units are Molar.

Volume of solution = 50 mL = 0.05 L

So, moles of Cu present = 0.142*0.05 = 0.0071

Mass of Cu = 0.0071*MW = 0.0071*63.54 = 0.451 g

So, %Cu in the brass washer = (0.451/0.6003)*100 = 75.13%

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