October 6, 2015

Homework Help: College Gen.Chemistry

Posted by Anonymous on Tuesday, March 25, 2014 at 5:29pm.

A student wanted to determine the amount of copper in a sample of copper ore. The student
dissolved a 2.500 0.001 g piece of copper ore in about 75 mL of nitric acid; then, a
complexing agent was added. The student transferred this solution to a volumetric flask and
used de-ionized water to fill to a final volume of 100.00 0.08 mL. From that volumetric
flask, the student transferred 15.0 mL of solution into a 250.00 0.08 mL volumetric flask
and diluted to the mark with de-ionized water. This final solution (from the 250.00 mL
volumetric flask) showed an absorbance of 0.545 0.004 at 610 nm in the spectrometer.
The student used a series of aqueous copper solutions of known concentration to generate a
calibration curve at 610 nm and obtained a best-fit line of y = (3,256)x + 0.007.
What is the % copper by mass in the ore sample from above with the correct significant figures?

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