Determination of Oxalate by Titration

Lab 9

Outline

0Purpose0Redox Reaction0Procedure0Calculation Sequence0Glassware Setup0Safety Concerns0Waste0Next Lab Reminder

Purpose

0Analyze three unknown samples for oxalate via titration.0Compare the analytical results of your redox reactions

with the percent oxalate in three known compounds.0 Identify the unknowns.0Gain 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)

Procedure0 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. 222 and 2230 Percent oxalate in your “known” compounds0 Moles of permanganate0 Moles of oxalate0 Mass of oxalate0 Percent oxalate present by mass0 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

0Oxalate solid goes in the garbage.0Pink, yellow and orange solutions must be disposed

in the acid waste container in the fume hood.0Purple solutions must go in the permanganate waste

container in the fume hood.0Small quantities of excess H2SO4 can be used in your

experiment.

Next Week – Lab 9 continued0Submit reports.