Determination of Equilibrium Constant

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SUMMARY

The discussion centers on determining the equilibrium constant (K) for the reaction Fe3+ + SCN- -> Fe(SCN)2+. The experiment utilized a calibration curve and Beer's law to establish the relationship between concentration and absorbance. Key requirements for the calibration curve include linearity and the necessity for it to pass through the origin. Changes in pH significantly affect the formation constant, with a decrease in pH leading to a lower K value and an increase in pH resulting in a higher K value.

PREREQUISITES
  • Understanding of Beer's law and its application in spectrophotometry
  • Knowledge of calibration curves and their significance in quantitative analysis
  • Familiarity with chemical equilibrium concepts, particularly formation constants
  • Basic principles of acid-base chemistry and its impact on equilibrium
NEXT STEPS
  • Study the principles of Beer's law in detail, focusing on linearity and calibration curves
  • Research the effects of pH on equilibrium constants in chemical reactions
  • Explore the role of concentration changes in shifting equilibrium positions
  • Investigate the preparation and analysis of solutions using Fe(NO3)3 and KSCN
USEFUL FOR

Chemistry students, laboratory technicians, and educators involved in chemical equilibrium studies and spectrophotometric analysis.

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I did an experiment in my Chem II class that required finding the equilibrium constant for this reaction

Fe3+ + SCN- ->Fe(SCN)2+

For the experiment, I had to use a calibration curve and Beer's law. How do I know that the calibration curve obeys Beer's law? I know that it would have to be a linear line, but are there other requirements?

To create this curve, I made solutions with Fe(NO3)3, KSCN, and HNO3. What would happen to the K value if I used water instead? Is it the acidity or the polarity that affects the equilibrium constant? How would I be able to increase or decrease a K value? Change the concentrations?
 
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For first part: straight-line, intersects the origin.

For second part: read your textbooks to properly study this, but if pH is decreased, formation constant will decrease; if increase the pH, then formation constant will increase.
 

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