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UNIT 2 MODULE 2 REDOX TITRATION SKILLS TESTED: None
Finding The Percentage of Iron in A Sa!"e of The Meta"
The amount of iron in a sample of its ore or of the metal(steel)
itself may be found by titrating an aqueoussolution derived from
the sample against a standard potassium manganate(VII) solution.
Potassium manganate
(VII) reacts quantitatively with iron(II) according to the half
equations:
n!"# (aq) $ % &$ ( aq) $ 'e# n$ (aq) $ "
&! (l)e $ (aq) e*$ (aq) $ e#
The sample in today+s e,ercise was obtained by dissolving a
sample of ## g of steel from our school wor-shopin dilute
sulphuric acid and then ma-ing up the solution formed to
$%d& with distilled water in a volumetric
flas-. fter mi,ing the solution thoroughly it was ready to be
titrated. The concentration of the anganate
'(II) *o"+tion is %,%2%% o" d-&,
Proced+re:
ill the burette to the /ero mar- with potassium manganate(VII)
solution. Pipette ' cm* of the iron(II) solutioninto an
0rlenmeyer flas-. dd 12 cm* of 1 sulphuric acid. 3ow run in
from the burette into the 0rlenmeyer
flas- the manganate(VII) solution with constant swirling of the
flas- and contents until one drop gives a permanent pin- end
point. 4epeat the titration as many times as is necessary to obtain
consistent results.
Ta."e of /+rette Reading*
Titration No, Ro+gh $ 2 &
Fina" Reading0c&
Initia" Reading0c&
(o"+e U*ed0c&
Tic1 the burette readings to be used in your calculation of the
aerage of the acc+rate .+rette reading*,
verage 5................. cm*
Treatent of Re*+"t*
$,6rite a balanced chemical equation for the reaction between
iron(II)ions and the n!"#ion.
2. 7alculate the number of moles of n!"# ions in the
average burette volume used.
&. (a)8se the result in 2 and the equation at $ to
calculate the no. of moles of iron(II) in ' cm *
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(b) in 1222 cm*
(c) &ence find the mass concentration of iron in the
solution
(d) 8se the answer in (c) to find the mass of iron dissolved in
the 12 dm*
". 9iven that ##g of steel were dissolved in the
$%d& of solutioncalculate the ; of iron in the steel.
', If some of the iron in the sample of steel was ALREAD3 in the
4& o,idation state how would still affect
the results and give a brief procedure which can be used to
determine the percentage of iron(II) and iron(III) present in
the sample of steel.
