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.