R 2 = .997 In-Lab Question 4. You desire to make a copper(II) solution at the sa

Question

R2 = .997

In-Lab Question 4. You desire to make a copper(II) solution at the same concentration as the unknown you just determined in Part A. How many grams of CuSO4 · 5 H2O are required to make 25.00 mL of this solution? Record the result as the target mass in Data Table B. (Enter your absorbance values to the 0.0001 decimal place.)

Data Table A. Calibration Curve of Cu2+ Solutions and Unknown Stock Cu2+ solution concentration           M Wavelength   nm Solution # Target Volume of Cu2+, mL Actual Volume of Cu2+, mL Target Volume of H2O, mL Actual Volume of H2O, mL [Cu2+], M (calculated) Absorbance at ~660 nm (measured to the 0.0001 decimal place) 1 1.50 1.50 6.50 6.50 .0934 .2347 2 3.00 3.00 5.00 5.00 .187 .4759 3 4.50 4.50 3.50 3.50 .280 .7445 4 6.00 6.00 2.00 2.00 .374 .9021 Equation of Trendline:   y = 2.48   x + ?

R2 = .997

Explanation / Answer

Concentration of the unknown Stock Cu2+ solution = 0.498 M

Volume of solution = 25 mL = 0.025 L

molarity = Moles of solute / Volume of solution

0.498 = Moles / 0.025

Moles = 0.498 * 0.025

= 0.01245

Molar mass of CuSO4.5 H2O = 249.685 g/mol

Mass of CuSO4.5 H2O required = 0.01245 * 249.685

= 3.108 g

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