Determination of Oxalate by Titration Lab 9

Outline Purpose Redox Reaction Procedure Calculation Sequence Glassware Setup Safety Concerns Waste Next Lab Reminder

Purpose Analyze three unknown samples for oxalate via titration. Compare the analytical results of your redox reactions with the percent oxalate in three known compounds. Identify the unknowns. 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) + 2e- Half 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 Start off with a known mass of unknown oxalate compound. Determine the moles of oxalate in the unknown by performing a titration with permanganate. 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. 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. 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 Percent oxalate in your “known” compounds Moles of permanganate Moles of oxalate Mass of oxalate Percent oxalate present by mass Percent error (experimental values compared to “known” values)

Glassware Setup

Safety Concerns Reagents: Inhalation: Ingestion: Skin Contact: Oxalate salts Potassium permanganate Sulfuric acid Sodium meta-bisulfite 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. Ingestion: Poisonous! Burns of the throat, mouth and stomach, nausea, vomiting, abdominal pain, edema, hypotension, circulatory collapse, gastric irritation, asthma, diarrhea, death. Skin Contact: Redness, itching, pain, burning, blurred vision, circulatory collapse, irritation, death. Eye Contact: Irritation, redness, pain, irreversible eye damage.

Waste Oxalate solid goes in the garbage. Pink, yellow and orange solutions must be disposed in the acid waste container in the fume hood. Purple solutions must go in the permanganate waste container in the fume hood. Small quantities of excess H2SO4 can be used in your experiment.

Next Week – Lab 9 continued Submit reports.