1 / 11

Experiment 22: Colorimetric determination of an equilibrium constant

Experiment 22: Colorimetric determination of an equilibrium constant. PURPOSE To determine the value of the equilibrium constant for the equilibrium system involving Fe 3+ ( aq ), SCN – ( aq ) and FeSCN 2+ ( aq ) using colorimetric analysis. THEORY.

alarice
Télécharger la présentation

Experiment 22: Colorimetric determination of an equilibrium constant

An Image/Link below is provided (as is) to download presentation 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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Experiment 22: Colorimetric determinationof an equilibrium constant PURPOSE To determine the value of the equilibrium constant for the equilibrium system involving Fe3+(aq), SCN–(aq) and FeSCN2+(aq) using colorimetric analysis.

  2. THEORY • In aqueous solution, Fe3+ ions react with SCN– ions to form the blood red coloured FeSCN2+ ion: • Fe3+(aq) (pale yellow) + SCN–(aq) (colourless)  FeSCN2+(aq) (red) • The colour of the solution is directly proportional to the concentration of FeSCN2+ ions present. The concentration of these ions can be determined by measuring the absorbance of the solution and comparing it with the absorbance of a solution of known concentration. If the initial concentrations of Fe3+ and SCN– are known, a value for the equilibrium constant, K, for the reaction can be calculated. • Colorimeters measure the amount of light that is transmitted or absorbed by a solution. A description of how they work can be found in your text book

  3. SAFETY PROCEDURES • Follow all instructions for using the equipment in this activity. • 2. Wear safety glasses and a laboratory coat for this experiment. • 3. Potassium thiocyanate is irritating to the skin and eyes. Avoid contact. • 4. The iron(III) nitrate solution used in this experiment contains nitric acid. The solution is irritating to skin and body tissues.

  4. Part 1. Preparation of Equilibrium Solutions • Label six 50.00 ml flasks 1-6 • Pipet 10.00 ml of .2M Fe(NO3)3 into each flask • Then pipet 1.00, 2.00, 3.00, 4.00, and 5.00 ml of .002M (NaSCN)- into flasks 2 – 6 respectively • Add .1M nitric acid to each flask to make a total of 50.00 ml per flask and stopper each flask

  5. Part 1. Preparation of Equilibrium Solutions • Calculate the final Fe(NO3)3 concentration and report them in part A • Calculate the final Fe(NCS)+2 concentration in each flask

  6. Part 1. Preparation of Equilibrium Solutions • Obtain 2 cuvettes, rinse one cuvette with soln 1, and discard in waste jar • Fill the rinsed cuvette with soln 1, insert cuvette into spectrophotometer and adjust 10 0 absorbance and 100 transmittance. • Rinse the second cuvette with soln 2 and discard in waste jar and measure the absorbance and transmittance of soln 2 at 447nm • Repeat procedures for soln 3 -6

  7. calibration curve • Prepare calibration curve by plotting absorbance vs concentration

  8. Part B: Determination of the calibration curve • Label six clean dry test tubes 1- 6 • Pipet 5.00 ml of .002M Fe(NO3)3 into each test tube • Then pipet 1.00, 2.00, 3.00, 4.00, and 5.00 ml of .002M (NaSCN)- into flasks 2 – 6 respectively • Add .1M nitric acid to each flask to make a total of 10.00 ml per flask and stopper each flask

  9. Part B: Determination of the calibration curve • Measure and record the absorbance and transmittance of these solns at 447nm • From your calibration curve determine the equilibrium concentration of Fe(NCS)+2

  10. Part B: Determination of the calibration curve

  11. Part B: Determination of the calibration curve

More Related