Lab+4+Analysis+by+Oxidation-Reduction+Titration

Title/Date: Analysis by Oxidation-Reduction Titration 11/13/11

Purpose: To standardize a potassium permanganate solution, then to use that standardized solution of potassium permanganate to analyze an unknown iron (II) solution.

Chemical Reactions: 8H2SO4 (aq) + 2K2MnO4(aq) + 5K2C2O4(aq) --> 2MnSO4(aq) + 10CO2(g) + 6K2SO4(aq) + 8H2O 8H2SO4 + 10FeSO4 +2KMnO4 --> 5F2(SO4)3 + 2MnSO4 + 8MnSO4 + K2SO4 Materials: 4 microtip plastic transfer pipettes milligram balance labels 10 mL Erlenmeyer flasks hot plate 3 M H2SO4 potassium permanganate solution standard potassium oxalate solution iron (II) salt (unknown)

Safety considerations: Safety goggles must be worn. The chemicals are highly corrosive, so handle the liquids with care and make syre not to spill any on skin and clothing. For disposal of the liquids containing manganese, transfer the liquids to a container for transition metals. Brown stains in the flasks should be clean out with 3 % hydrogen peroxide. Do not put unused reagents back in their originalbottle. Excess potassium oxalate can be poured down the drain as well as the unknown solution after it is neutralized.

Procedure: Obtain 3 pipettes and label them. Label one acid(3 M H2SO4), one perm (KMnO4), and ox (oxalate standard). Fill each pipette with the substances given and record the masses of the filled pipettes, excluding the oxalate solution. Add between 1.0 and 1.5 grams of ox in a graduated cylinder from the pipette and an equal amount of acid from the pipette. Warm on the hotplate and add perm to the liquid from the pipette while swirling and heating every 30-45 seconds. Add perm until liquid turns pink for at least 30 seconds. Weigh the perm and ox pipettes. Repeat twice more. For part B, weigh a sample of the iron (II) salt between 0.6 and 0.7 grams. Dissolve the salt in a 25 mL flask filled half way with water. Add three drops of phosphoric acid and enough 3 M H2SO4 to fill half of the remaining volume. Fill a pipette with the unknown Fe salt and label it Fe. Weigh the pipette and contents, then refill the perm pipette and weigh it. Titrate the iron salt and repeat two more times for three trials.

Data Tables:
 * || Trial 1 || Trial 2 || Trial 3 ||
 * Initial mass of PERM pipette || 1.2613 g || 1.1172 g || 1.5377 g ||
 * Final mass of PERM pipette || 1.1172 g || 0.9927 g || 1.3450 g ||
 * Mass of PERM || 0.1441 g || 0.1245 g || 0.1927 g ||
 * Initial mass of OX pipette || 1.3518 g || 1.0710 g || 1.2110 g ||
 * Final mass of OX pipette || 1.0710 g || 0.8328 g || 0.8622 g ||
 * Mass of OX || 0.2808 g || 0.2382 g || 0.3488 g ||
 * moles of Na2C2O4/g OX || 4.94 x 10^ -3 mol/g || 4.91 x 10^ -3 mol/g || 4.80 x 10^-3 mol/g ||
 * Moles of OX delivered || 0.001689 mol || 0.001433 mol || 0.002098 mol ||
 * Moles of KMnO4 || 9.118 x 10^ -4 mol || 7.878 x 10^ -4 mol || 1.219 x 10^-4 mol ||
 * conc. of PERM in mol KMnO4/g solution || 2.146 x 10^ -3 mol/g || 2.172 x 10^ -3 mol/g || 2.243 x 10^ -3 mol/g ||
 * Average PERM conc. in moles KMnO4/ g solution ||  || 2.187 +/- 0.000037 mol/g ||   ||
 * Avergae PERM conc. including avg. deviation ||  || 0.002187 +/- 0.000037 mol/g ||   ||


 * || Trial 1 || Trial 2 || Trial 3 ||
 * Initial mass PERM pipette || 1.3450 g || 1.4468 g || 1.1346 g ||
 * Final mass PERM pipette || 0.9991 g || 1.1346 g || 0.7566 g ||
 * Mass of KMnO4 used || 0.3459 g || 0.3122 g || 0.3780 g ||
 * Moles of KMnO4 used || 0.002189 mol || 0.001975 mol || 0.002392 mol ||
 * Moles of Iron present ||  ||   ||   ||
 * Initial mass of FE pipette || 1.4930 g || 0.9452 g || 1.1158 g ||
 * Final mass of FE pipette || 0.9452 g || 0.4855 g || 0.4895 g ||
 * Mass of Iron solution used || 0.5478 g || 0.4597 g || 0.6263 g ||
 * Conc. of iron(mol Fe+2/g solution) || 0.01097 mol/ g of solution || 0.01060 mol/ g of solution || 0.01116 mol/ g of solution ||
 * % iron in unknown ||  ||   ||   ||
 * Avg. % iron ||  ||   ||   ||
 * Avg. % of iron w/ avg. deviation ||  ||   ||   ||

Calculations/ Results: Questions/Problems: Prelab 1) a) H2SO4 + KMnO4 + K2C2O4 --> MnSO4 + CO2 + K2SO4 + H2O KMnO4 + 5e- --> MnSO4 K2C2O4 --> 2CO2 + 2e- **8H2SO4 + 2KMnO4 + 5K2C2O4 --> 2MnSO4 + 10CO2 + 6K2SO4 + 8H2O** b) The reducing agent is K2C2O4 and oxidizing agent is KMnO4. c) There are 2 moles of potassium permanganate per 5 moles of potassium oxalate. There are 8 moles of sulfuric acid per 2 moles of potassium permanganate. The concentration of oxalate solution is given in moles of K2C2O4 solution per gram of potasium oxalate solution. 2) H2SO4 + FeSO4 + KMnO4 --> Fe2(SO4)3 + MnSO4 + H2O 2FeSO4 --> F2(SO4)3 + 2e- KMnO4 + 5e- --> MnSO4 3) % by mass Fe = (part/whole) x 100 = (55.85 g Fe / 278.022 g FeSO4 * H2O) x 100 = **20.1 % Fe** 4) The dilute aqueous solution will have a mass between 25 and 26 when the volume is 25 mL because the molar mass of the solution is significantly larger than water.
 * 8H2SO4 + 10FeSO4 + 2KMnO4 --> 5Fe2(SO4)3 + 2MnSO4 + 8MnSO4 + K2SO4**