Equilibrium Constant Today’s Experiment: Fe 3+ (aq) + HSCN(aq) FeSCN 2+ (aq) + H + (aq) orange colorless dark red colorless Determine [FeSCN 2+ ] using Spec20 and Beer’s Law
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Fe3+(aq) + HSCN(aq) FeSCN2+(aq) + H+(aq)
orange colorless dark red colorless
3. We will use test tubes #1-5 to make a calibration curve using Beer’s Law
4. Excess Fe3+ (0.200 M) pushes the reaction to the right: [HSCN]o = [FeSCN2+]
5. We must use Fe3+ solution as a blank to cancel out Fe3+ absorbance
6. Record %T and calculate A for the five different [HSCN] concentrations
7. Plot A vs. [FeSCN2+] to give a straight line. Calibration Curve
8. Once you find the Absorbance of any other [FeSCN2+] solution, you can find its concentration from the calibration curve.
Slope = el
Slope = -DH/R
Intercept = DS/R
V. Procedure for finding DH, DS, and DG (Tubes #6-9 at different T’s)