Transcript Determination of Oxalate by Titration

Determination of Oxalate by
Titration
Lab 9
Outline
0 Purpose
0 Redox Reaction
0 Procedure
0 Calculation Sequence
0 Glassware Setup
0 Safety Concerns
0 Waste
0 Next Lab Reminder
Purpose
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)
Procedure
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
(2:5).
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.
Waste
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
experiment.
Next Week – Lab 9 continued
0 Submit reports.