# Equilibrium Constant Today’s Experiment: - PowerPoint PPT Presentation

1 / 4

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

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Equilibrium Constant Today’s Experiment:

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

#### Presentation Transcript

Equilibrium Constant

• Today’s Experiment:

Fe3+(aq) + HSCN(aq) FeSCN2+(aq) + H+(aq)

orange colorless dark red colorless

• Determine [FeSCN2+] using Spec20 and Beer’s Law

• Determine the other concentrations from an ICE Table

• Calculate K at three different Temperatures

• Use the Temperature data to determine DH, DS, and DG for the reaction

• Take a look at the Pre-Lab Problems

• Beer’s Law and Making a Calibration Curve

• Colored compounds absorb light that is shined through them

• A = elCAbsorbance = (Extinction Coefficient)(length)(Concentration)

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

A

[FeSCN2+]

• Procedure for finding K (Tubes #6-9)

• Make 4 different solutions of HSCN, Fe3+

• Find A with the Spec20

• Find [FeSCN2+] from the Calibration Curve

• Use an ICE Table to find all the other concentrations

• All solutions are made with 0.500 M HNO3, so [H+] = 0.500

• Other initial concentrations are found using the Dilution Equation

Slope = -DH/R

Intercept = DS/R

lnK

1/T

V. Procedure for finding DH, DS, and DG (Tubes #6-9 at different T’s)

• You will use the same tubes (#6-9) at an ice bath (around 5 oC)

• Hot tap water bath temperature (around 45 oC) [Not too hot! Boils off HSCN!)

• You already have the room temperature data from these tubes (around 25 oC)

• Plot lnK vs. 1/T for your three different temperatures

• Use the following equations to calculate DH, DS, and DG for the reaction

• Notes:

• Use parafilm to cover the test tubes as you mix the solutions thoroughly

• Spec20: 0% with nothing in it; 100% with Iron Solution only as Blank

• Fill cuvet with most dilute first, rinse with next most dilute, and so on