Korea Advanced Institute Science and Technology

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Exp 3. Colorimetric Determination of Iron

• Korea Advanced Institute Science and Technology
• General Chemistry Laboratory II

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PART A. Preparation of the Calibration Curve

• Using a pipette, add 1, 2, 3, 4, 5mL of standard
  iron solution to
• each of
  five clean, dry 50mL volumetric flasks.
• Add 1 mL of 1 M ammonium acetate,
• 1 mL of 10 hydroxylamine
  hydrochloride,
• and 10mL of 0.30 o -
  phenanthroline solution, successively.
• Dilute to exactly 50 mL with distilled water .
• Mix well to develop the characteristic
  orange-red color of the iron(II)-phenanthroline
  complex.

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• Allow the color to develop for 45 min.
• Measure the absorbance of these solutions at
  510nm and plot the absorbance versus
  concentration to construct your calibration
  curve.
• Plot the absorbance versus concentration to
  construct your calibration curve.

A cap
Disposable cuvette
Sample holder
Before inserting the cuvette into the sample
holder of the spectrometer, be sure to close the
mouth of the cuvette with the cap every time.
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PART B. Determination of Iron

• Accurately weigh out about 0.1 g to four
  significant figures of the iron unknown into a 50
  mL volumetric flask.
• Add five drops of 6 M sulfuric acid (CAUTION! Be
  careful ! Sulfuric acid is a strong acid.), and
  dilute to exactly 50 mL.
• Pipet exactly 1mL of this solution into three
  additional 50 mL volumetric flasks.
• (Repeat the procedure described in PART A)
• Add 1 mL of 1 M ammonium acetate,
• 1 mL of 10 hydroxylamine
  hydrochloride,
• and 10mL of 0.30 o-
  phenanthroline solution, again.
• Dilute to exactly 50 mL with distilled water.
• (Mix well to develop the characteristic
  orange-red color of the iron(II)-phenanthroline
  complex.)

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• Allow the color to develop for 45 min.
• Measure the absorbance of these solutions at
  510nm plot versus concentration to construct your
  calibration curve.
• Using the observed absorbance and calibration
  curve,
• Calculate the milligrams of iron
  in 1 mL of solution.
• the percentage
  of iron in the sample.
• the mean and
  standard deviation of your results.

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How to operate the spectrometer. Your TA will
demonstrate this.
1) Turn on the spectrophotometer and the computer
that runs it. Allow the spectrophotometer to warm
up for 30 minutes before use. Start the program
by double-clicking VisualSpectra2.1-Sr on the
desktop.
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2) Add distilled water in a cuvette as a
reference. Insert it sample holder. Be sure to
cover sample holder.
3) Move the shutter button toward off. (UV
Visible On)
4) Click the GO button. (Initialize the
detection system and get ready to start.)
5) Click the DARK button . (To obtain a dark
spectrum without a light source.)
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6) Move the shutter button toward ON. (UV
Visible On)
7) Click the refer button. ( To get the
reference spectrum under the light source.)
The ABSORBANCE MODE has been activated.
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8) Click the ABSOR button.
9) Type 510 in the blank of Wavelength.
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10) Fill the cuvette with sample solution, and
then close the mouth of the cuvette with a lid.
Insert it into the chamber. Close the sample
cover again. (Make sure there are no bubbles in
the cuvette. To remove bubbles, tab the cuvette
gently with your finger.)
11) Click the gtgt button. After a few moments,
the absorbance will be displayed on the
right box. Record the data on your report sheet.
12) Repeat step 10-11 with your remaining
samples.