Chem 152 Lab 2

Calibration Curves and an Application to Beer's Law

Demonstration

Below are many of the experimental steps you will perform in this lab. Be sure to consult the procedure for the detailed instructions. Click on an image to open an enlarged view.

1.
Ferroin stock solution

Obtain 5 mL of the ferroin stock solution in a beaker from the automatic dispenser in the hood.

2.
digital pipettor and ferroin stock solution

Use the digital pipettor, with a blue pipet tip, to transfer a portion of the ferroin stock solution to the 10 mL volumetric flask in order to make your first ferroin standard solution.

3.
diluting ferroin stock solution

Dilute the stock solution with DI water to the calibration mark on the neck of the flask, making sure that the bottom of the meniscus sits directly on the mark. Cap the flask and invert it several times to mix the solution thoroughly.

4.
transferring ferroin standard to cuvette

Transfer a portion of the solution to a clean, labeled cuvette to rinse it and pour that rinsing down the drain. Then fill the cuvette again (3/4 full) and set this aside. The remainder of the solution can go down the drain. Rinse the volumetric flask well and repeat steps 2-4 outlined on this page until you have prepared all 5 standard solutions.

5.
weighing out crushed iron tablet

For the preparation of the iron sample in Part II, weigh out ~20 mg of the crushed iron tablet and transfer it to a beaker. Make sure to record the required information listed on the bottle label.

6.
add HCl

Add 0.1 M HCl to the beaker using the automatic dispenser in the hood, as well as ~10 mL of DI water.

7.
stir and heat beaker containing iron tablet, HCl and water until boiling

Add a stir bar and heat the solution, while stirring, until it boils. Then turn off the heater and let it cool.

8.
pulling cooled solution into syringe

Pull the cooled iron tablet solution into the 5 mL plastic syringe. (This is easiest if one person holds the beaker and the other works the syringe.)

9.
deliver solution to flask through filter attached to end of syringe

Twist the 0.45 micron filter onto the tip of the syringe and then push the solution through the filter, delivering it to a clean, 100 mL volumetric flask. Add some water to the beaker to rinse it and ensure all of the iron tablet solution is being collected. Transfer the rinsing to the volumetric flask using the same process of drawing it into the syringe (no filter on the end), replacing the filter, and pushing the solution through the filter into the flask.

10.
dilute filtered solution to mark on neck of volumetric flask

Dilute the iron tablet solution with DI water to the calibration mark on the neck of the flask. Cap the flask and invert it several times to mix the solution thoroughly. Then pour the solution into a clean, dry beaker.

11.
pull 5mL of diluted iron solution into volumetric pipet

Use the pipet bulb to pull diluted iron tablet solution from the beaker into a 5 mL volumetric pipet, making sure to pull it a little ways above the calibration mark on the pipet. Quickly, but carefully, remove the bulb and place your finger tightly over the opening at the top of the pipet to prevent any solution from draining out the bottom.

12.
up close veiw of meniscus in volumetric pipet

Carefully loosen your finger at the top of the pipet to let the extra solution slowly drain from the pipet back into the beaker until the meniscus is directly on the calibration mark on the pipet.

13.
deliver 5 mL from volumetric pipet to new volumetric flask

Carefully let the 5 mL of diluted iron tablet solution drain into a clean, 100 mL volumetric flask.

14.
add hydroxylamine hydrochloride to flask containing 5 mL iron solution

Using the automatic dispenser in the hood, add 0.23 M hydroxylamine hydrochloride to the flask containing the 5 mL of diluted iron tablet solution.

15.
add sodium acetate to flask containing iron and hydroxylamine HCl

Using the automatic dispenser in the hood, add 1.0 M sodium acetate to the flask containing the diluted iron tablet solution and hydroxylamine hydrochloride.

16.
adding phen solution to the iron/reagent mixture in the flask

Using the automatic dispenser in the hood, add 1,10-phenanthroline solution to the flask containing the diluted iron tablet solution, hydroxylamine hydrochloride, and sodium acetate. This last additon will begin to form the colored ferroin complex that you will notice starting to appear (this is the same ferroin complex in the standard solutions you prepared in Part I).

17.
dilute reaction mixture in flask to the mark on the neck of the flask

Dilute the solution with DI water to the calibration mark on the neck of the flask. Cap the flask and invert it several times to mix the solution thoroughly. It will take 5-10 minutes for the ferroin solution to form completely, so let the solution sit for some time after you have mixed it well.

18.
transfer the ferroin complex to a cuvette

Transfer a portion of the solution to a clean, labeled cuvette Note: the solution you prepare in Part II cannot go directly down the drain. Follow the instructions in the manual for disposing of this solution when you are finished with the experiment.

19.
spectrometer station

Take all 6 cuvettes to the spectrometer station and place the first cuvette in the spectrometer, which is shown in the lower left corner of this picture, such that the path of the light beam goes through the clear sides of the cuvette.. You will see a curve, similar to the one shown here, appear on the computer screen. Move the vertical cursor to the highest point on the peak. Record that wavelength, as well as the magnitude of the absorbance (both shown in the bar in the lower right corner of the screen). Measure and record the absorbance (at the same wavelength) for the remaining standard solutions and the sample solution.

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