9-8 9 SPECTROPHOTOMETRIC ANALYSIS NAME Pre-Lab Assignment 1315 Section NOTE: The
ID: 1029915 • Letter: 9
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9-8 9 SPECTROPHOTOMETRIC ANALYSIS NAME Pre-Lab Assignment 1315 Section NOTE: The data used here are A. CONSTRUCTION OF A CALIBRATION CURVE Record the concentration of the stock Co solution. EXAMPLE: 3.63 mg Co ImL soln PRACTICE: 4.32 mg Co /mL soln Determine the concentration of Co in tubes A-D' using the dilution formula. Show an for illustrative purposes. The data you obtain will be different illustrative calculation using tube 'A' as an example. Enter the results in the table. EXAMPLE: 0.726 mg/mL Volume of stock Concentration of dilute ubeo taken, mL Co solution, mg'ml Absorbance 2.00 4.00 6.00 8.00 0.726 1.45 2.18 2.90 0.092 0.186 0.280 0.372 PRACTICE Tube Volume of stock Concentration of dilute Co taken, mL Co solution, mg/mL tion of dilute Absorbance 2.00 4.00 6.00 8.00 0.113 0.225 0.335 0.447 Construct a calibration curve by graphing absorbance versus Co concentration using the data from tubes A-D. (Note: the Excel graphing template SPECTRAL 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 on p D1.) B. EXPERIMENTAL DETERMINATION OF MASS PERCENT Record all mass measurements made in the cobalt determination. Report the mass of cobalt compound used. EXAMPLE: The empty flask weighs 128.583 g. The flask and cobalt compound weigh 129.189 g. The cobalt compound weighs 0.606 g PRACTICE: The empty flask weighs 143.677 g. The flask and cobalt compound weigh 143.957 gExplanation / Answer
Practice : Co2+ solution =4.32 mg/ml=Cstock
tube A:
volume of stock=2.00ml=Vstock
volume of dilute sol=10ml=Vdil
Concentration of dilute Co2+ solution=Cstock*Vstock/Vdil=4.32mg/ml*(2.00ml/10.00ml)=0.864mg/ml
tube B:
volume of stock=4.00ml=Vstock
volume of dilute sol=10ml=Vdil
Concentration of dilute Co2+ solution=Cstock*Vstock/Vdil=4.32mg/ml*(4.00ml/10.00ml)=1.728mg/ml
tube C
volume of stock=6.00ml=Vstock
volume of dilute sol=10ml=Vdil
Concentration of dilute Co2+ solution=Cstock*Vstock/Vdil=4.32mg/ml*(6.00ml/10.00ml)=2.592mg/ml
tube D
volume of stock=8.00ml=Vstock
volume of dilute sol=10ml=Vdil
Concentration of dilute Co2+ solution=Cstock*Vstock/Vdil=4.32mg/ml*(8.00ml/10.00ml)=3.456mg/ml
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