OF IRON IN AN ORE
1. The student will use chemical principles to dissolve
an iron ore.
2. The student will pre-treat the sample to obtain
the iron in the reduced(+2 oxidation) state.
3. The student will use a strong oxidant as the titrant.
4. The student will use a solution of primary standard
as the titrant.
Preparation of 0.016 M Potassium Dichromate
Weigh out approximately 0.008 mole of dry K2Cr2O7
(100o C for drying) on the analytical balance. Dissolve in water
and dilute to 500 ml. in a volumetric flask.
Preparation of Preventive Solution
Preventive solution is a strong acid solution which
is used to prevent bad results. It is 4-5 M in H2SO4
and a 1-1.5 M in H3PO4. In a pyrex beaker add in
order with stirring 400 ml. distilled water; 60 ml. 18M sulfuric acid;
40 ml. 15 M phosphoric acid. After cooling to room temperature, store in
a glass bottle.
Determination of the Iron
Weigh a 0.7 g samples of ore into 500 mL erlenmeyer
flasks. Since the iron ore is very hygroscopic, weigh the sample
on the same day you dry it. Plan to run 4 or 5 samples so that you
will have 3 good ones to report. Have DRY erlenmeyer flasks for ease of
Dissolving the Ore Sample
Add 10 ml. conc. (12 M) HCl and 3 ml. stannous chloride.
Heat on a hot plate until no colored ppt. remains. This should be under
NOTE: From this point on do only one sample at a
time. Each sample will probably take from 30 to 45 min. The sample must
be taken to completion today if it is carried past this point.
Reduction of Iron (III) to Iron (II)
If the solution is yellow in color, add stannous
chloride to the hot (nearly boiling) solution. Add until the solution is
colorless, then add 2 to 3 drops in excess. Immediately place in ice bath.
IF MORE THAN 4 DROPS OF EXCESS STANNOUS WAS ADDED AND
If the solution is colorless, all of the iron is reduced and excess Sn2+
may be present. Add one or two crystals of KMnO4. Be sure that
they all dissolve completely. Continue to add the crystals until one crystal
turns the solution yellow. All of the excess stannous chloride has been
destroyed. Add stannous chloride drop-wise until the solution is colorless.
Add two drops in excess.
Cool in an ICE BATH until the solution is from 5-10o
C. Add 75 ml. of ice cold (5 - 10o C) preventative solution
and 200 ml. of cold water. Add 10 ml. of saturated (you should see particles
in bottle) mercuric chloride fast, using a graduated cylinder. Swirl for
1/2 to 1 minute. Let the solution stand for 5 min. in the ice bath. If
you have no silky ppt., note this on your results. Add 6 drops of Barium
Diphenylamine sulfonate indicator. Titrate to the first violet or purple
color. In calculating subtract 0.05 ml. for an indicator blank.
Calculate percent iron in ore. Include computer print-out
for the calculation. Check pages 372-3 of your text to see the chemical
CAUTION: The iron ore should be dried on the
day it is weighed.
This may mean re-drying the sample.
DO NOT OVER DRY THE SAMPLE!
SAFETY AND DISPOSAL INFORMATION: Dispose of all test
solutions and precipitates in the "IRON EXPERIMENT WASTE" container.
CAUTION: Remember to treat all chemicals with respect.
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