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Katarina Ong
Connor Wilson
Mike Oliver
April 8,2014
Redox Titrations with Potassium Permanganate
Experimental Background
The purpose of this laboratory investigation was to determine the mass-percent of iron in an
unknown sample by titrating with an oxidizing agent
...
By reacting the potassium permanganate with
the unknown concentration of Iron in a solid sample, the percent iron in the sample may be
determined, demonstrating multiple uses of titration data and a foray into Oxidation-Reduction
Reactions
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The 50mL burette contains the
potassium permanganate solution, and the erlenmeyer flask rests on a hot plate, so that both
the heating and stir functions could be utilized
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Three samples of
roughly 1g of oxalic acid dihydrate were measured using an analytic balance (exact masses
shown in ​Table 1​) and each transferred into a 250mL Erlenmeyer Flask
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As shown in ​Figure 1​, a buret was set up on a
stand in order to deliver a measured quantity (in mL) of the Potassium Permanganate solution
to the known quantity of the acid
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Each trial beaker was warmed on a hot plate to roughly 60 degrees Celsius
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A titration was performed by slowly adding the permanganate solution until the
solution was a persistent pink-purple color
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0207M for the Potassium
Permanganate solution
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A 50mL buret was set up on a buret stand, using a burette clamp, and filled to the
0
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A 250mL beaker was filled with roughly 50mL of dilute sulfuric acid, and about 3 mL of
phosphoric acid, and a sample of about 0
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This solution was placed on a hot plate under the buret setup (this titration was not heated, only
the stir function was utilized here)
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Again, a
standard titration was performed slowly adding the permanganate to the unknown solution until
the solution had a persistent pink-purple color
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Data Collection:
Table 1:​ Oxalic acid was dissolved in 50 mL of sulfuric acid
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Beaker #

Mass oxalic acid (g)

Potassium permanganate
used (mL)

1

0
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75

2

0
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04

3

0
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54

This standardization yielded the concentration of the potassium permanganate
...

ex
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104 g oxalic acid ×
3
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01875 L

1 mol oxalic acid
108
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85 × 10−4 moles KM nO4

= 0
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0205+
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0209
3

=
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5 grams were titrated with potassium permanganate
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Trial

Mass of unknown compound
(g)

Potassium permanganate
delivered (mL)

1

0
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65

2

0
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63

3

0
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28

From this titration, the number of grams of iron (II) within each sample was determined using the
molarity of potassium permanganate from the standardization and the stoichiometric coefficients
of M nO4 − and F e2+ from the chemical equation:
2M nO4 − + 5F e2+ + 8H + → 2M n2+ + 5F e3+ + 4H 2 O
ex
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207 mol M nO4 −
1L

× 0
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85 g F e2+
1 mol F e2+

= 0
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Data Processing:
Table 3:​ To determine the percent of iron within each sample, the grams of iron were divided by
the total weight of the sample
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0846

0
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5

2

0
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505

16
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0825

0
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5

ex
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0846 g
0
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5% iron in sample

The average percentage of iron in the unknown compound was calculated as such:
16
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8+16
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6%
3
avg
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6%

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Conclusion
The purpose of this investigation was to determine the mass-percent of iron in an unknown solid
sample
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The potassium permanganate was
then titrated into a solution containing a measured quantity of the unknown iron-bearing solid
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This visual indication was also helpful in
standardizing the potassium permanganate
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By
measuring the quantity of potassium permanganate delivered to the unknown solution, as well
as the mass of the unknown solid dissolved in solution, it was possible to calculate the exact
mass-percent of iron in the unknown solution using stoichiometry and the balanced chemical
equation
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6 percent
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Though this issue was likely mostly avoided by
beginning the titrations immediately after the unknown solid was dissolved in solution, any
discernable effect would be seen as a lowering of the calculated value for the mass-percent of
iron in the unknown solid

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