Determination of Oxalate by Titration

Determination of Oxalate by
Lab 9
0 Purpose
0 Redox Reaction
0 Procedure
0 Calculation Sequence
0 Glassware Setup
0 Safety Concerns
0 Waste
0 Next Lab Reminder
0 Analyze three unknown samples for oxalate via titration.
0 Compare the analytical results of your redox reactions
with the percent oxalate in three known compounds.
0 Identify the unknowns.
0 Gain experience in completing a titration without the use
of a formal indicator.
Redox Reactions
Half reaction for the oxidation of C2O42-:
C2O42-(aq)  2CO2(g) + 2eHalf reaction for the reduction of Mn7+:
8H+(aq) + MnO4-(aq) + 5e-  Mn2+(aq) + 4H2O(l)
Complete reaction:
16H+(aq) + 5C2O42-(aq) + 2MnO4-(aq)  10CO2(g) + 8H2O(l) + 2Mn2+(aq)
0 Start off with a known mass of unknown oxalate compound.
0 Determine the moles of oxalate in the unknown by performing a
titration with permanganate.
0 At the point where all the oxalate has reacted with the
permanganate we are adding by way of the buret, we see a color
change from yellow to light pink.
0 This end point is indicative of passing the equivalence point
slightly. An end point error is introduced and needs to be
minimized as much as possible.
0 From the known concentration and measured volume of
permanganate added, we calculate the moles of oxalate, keeping
in mind our stoichiometric ratio given by the complete reaction
Calculation Sequence
Sample calculations are on pp. 214 and 215
0 Percent oxalate in your “known” compounds
0 Moles of permanganate
0 Moles of oxalate
0 Mass of oxalate
0 Percent oxalate present by mass
0 Percent error (experimental values compared to
“known” values)
Glassware Setup
Safety Concerns
0 Reagents:
 Oxalate salts
 Potassium permanganate
 Sulfuric acid
 Sodium meta-bisulfite
0 Inhalation:
 Poisonous! Nervousness, cramps, CNS depression, burns / irritation to
respiratory tract, irritation of nose and throat, difficulty breathing, lung
edema, damage to mucosa, coughing, shortness of breath, allergic reaction.
0 Ingestion:
 Poisonous! Burns of the throat, mouth and stomach, nausea, vomiting,
abdominal pain, edema, hypotension, circulatory collapse, gastric
irritation, asthma, diarrhea, death.
0 Skin Contact:
 Redness, itching, pain, burning, blurred vision, circulatory collapse,
irritation, death.
0 Eye Contact:
 Irritation, redness, pain, irreversible eye damage.
0 Oxalate solid goes in the garbage.
0 Pink, yellow and orange solutions must be disposed
in the acid waste container in the fume hood.
0 Purple solutions must go in the permanganate waste
container in the fume hood.
0 Small quantities of excess H2SO4 can be used in your
Next Week – Lab 9 continued
0 Submit reports.

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