Question

Tips for Lab Discussion • Discuss calibration curve and slope determined. Discuss concentration of copper found. Discuss percent of copper in brass sample calculated. Discuss sources of success or error encountered during the experiment Practice Problems 1- Why is a calibration curve constructed? 2- If you used a dirty cuvette when reading when the calibration curve, would this raise or lower the value of the slope? Explain. 3- If unknown to the student, the standard CuSO4.5H2O solution was prepared using 200.0 mL instead of a 100 mL volumetric flask, how this error would affect the calculation of the molarity of the stock solution? Explain in detail. 4- If 1.455 g of brass unknown were dissolved in 8 M HNO3, diluted to 100 mL in a volumetric flask with distilled water, filtered, and found to have a 0.123 M Cu2+, what is the percent of copper in the brass sample?

Answer 1

1.calibration curves are used to determine the concentration of unknown substance based on previous measurement of solution of known concentration . The precision and accuracy of the measurement depends on the curve.

2.If we used dirty cuvette in spectrophotometer then less light is reached in sample of spectrophotometer therefore the machine will interpret this as more light absorbed this will raise the value of slope.

3.