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The data used here are for illustrative purposes. The data you obtain will be different. Note: The data u C DETERMINATION OF COPPER Preparation of a Stock Cu2+ Solution ord the mass of copper wire used. Use this datum in conjunction with volume of the volumetric flask to determine the concentration of Cul in the stock solution. Express this concentration as mg Cu/mL solution. EXAMPLE: The mass of copper wire is 0.236 g (236 mg): the concentration of Cup in the stock solution is 2.36 mg/mL. PRACTICE: The mass of copper wire is 0.181 g. Constructing a Calibration Curve Determine the concentration of Cum in tubes 'AVD' using the dilution formula Show an illustrative calculation using Tube 'C' as an example. Enter the results in the table below. EXAMPLE: 1.42 mg Cu/mL soln Tube Absorbance A Volume of stock Cu2+ taken, mL 2.00 4.00 6.00 8.00 Concentration of dilute Cu2+ solution, mg/mL 0.472 0.944 1.42 1.89 C D 0.147 0.306 0.451 0.595 PRACTICE: Tube Concentration of dilute Cu solution, mg/ml Absorbance Α B C Volume of stock Cu2. taken, mL 2.00 4.00 6.00 8.00 0.113 0.221 0.350 0.455 Construct a calibration curve by graphing absorbance versus Cum concentration using the data from tubes A-D. (Note: the Excel graphing template COPPER ANALYSIS is only available on the lab computers. You can construct your own graph in Excel following the directions given in the Excel Graphing Primer, p D1.) EXAMPLE: The regression line from Excel is y = 0.3148x + 0.0028. (The underlined digit is not a significant figure but carried along to minimize rounding errors.) PRACTICE:

Answer 1

Practice 1.

Mass of Cu²⁺ in tube A = 2 mL * 0.472 mg/mL = 0.944 mg

Mass of Cu²⁺ in tube B = 4 mL * 0.944 mg/mL = 3.776 mg

Mass of Cu²⁺ in tube B = 6 mL * 1.42 mg/mL = 8.52 mg

Mass of Cu²⁺ in tube B = 8 mL * 1.89 mg/mL = 15.12 mg

Therefore, the average mass of Cu²⁺ = (0.944 + 3.776 + 8.52 + 15.12) mg/(2+4+6+8) mL = 1.418 mg/mL