PERMANGANATE VERSUSOXALATE

Reporters: Ken Alexander P. BautroLarry Andrew L. GaleonNece Jean P. TagamMary Jann Kestle Z. Tamayo

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OBJECTIVES:

To prepare 0.72N Sulfuric acid (H2SO4);

To standardize a Permanganate solution against Primary Standard Sodium Oxalate (Na2C2O4);

To calculate % Na2C2O4 in unknown sample.

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MATERIALS/CHEMICALS:Materials: Bunsen burner, clay

pot, wire gauze, asbestos mat, brown bottle, balance, graduated cylinder, beaker, thermometer, stirring rod, buret, buret clamp, iron stand.

Chemicals: H2C2O4, MnO4-

solution, H2SO4, Na2C2O4

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SCHEMATIC DIAGRAM:

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CALCULATIONS:For preparation of .72N H2SO4

.72N H2SO x =0.36M H2SO4

9N H2SO4 x = 4.5 M H2SO4

M1V1=M2V2

(4.5 M H2SO4) (V1) = (0.36M H2SO4) (0.250L H2SO4)

V1 = .02L or 20mL H2SO4

 

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CALCULATIONS:

For preparation 250mL Permanganate solution

= 0.8 g KMnO4

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Concentration of KMnO4 can be computed by:

CKMnO4 = (g Na2C2O4)(MNa2C2O4)(Molar ratio)

L KMnO4

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BACKGROUND: The permanganate ion, MnO4

-, is a powerful oxidizing agent. It reacts to form Mn2+ ion

MnO4- + 8H+ +5e- ----> Mn2+ + 4 H2O

So the Manganese goes from an oxidation state of +7 to +2

Each MnO4- ion will therefore consume 5 electrons It will oxidize another species, stealing the 5 electrons in the process

Since H+ is also consumed, the reaction will need to be done in an acidic solution.

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BACKGROUND: The Oxalate ion is stable, but can be oxidized

C2O42- --------> 2 CO2 + 2e-

• The C in oxalate is in an oxidation state of +5• The C in CO2 has an oxidation state of +4

• So each carbon will release 1 electron • Each oxalate will release 2 electrons • Equation for the oxidation of oxalate by permanganate in acidic solution:2 MnO4

-(aq ) + 5 H2C2O4(aq ) + 6 H3O+(aq ) --> 2Mn2+(aq ) + 10 CO2(aq ) + 14 H2O

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AUTOCATALYSIS: REACTION OF PERMANGANATE WITH OXALIC ACID

A dilute purple solution of potassium permanganate is added to each of two beakers of acidified oxalate solution. A few crystals of manganese(II) sulfate added to the solution on the right catalyze the reduction of permanganate to colorless manganese(II) ion. Note the initial red color due to formation of a manganese(III) intermediate in the beaker on the right.

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POTASSIUM PERMANGANATE IS ADDED.

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MANGANESE(II) SULFATE IS ADDED TO THE SOLUTION ON THE RIGHT.

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IT CATALYZES THE REDUCTION OF PERMANGANATE TO COLORLESS MANGANESE(II) ION.

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THE OTHER SOLUTION'S REACTION RATE EVENTUALLY INCREASES AS IT FORMS MANGANESE(II) ION, WHICH SUBSEQUENTLY AUTOCATALYZES ITS OWN FORMATION.

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FINDING THE ENDPOINT:

In addition to being a strong oxidizing agent, Permanganate has another important property. It is a compound with an intense purple color. Even one drop of our titrant, KMnO4, is enough to produce a strong pink color. In this case we simply titrate until the solution remains pink.

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ENDPOINT:Pre

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RUNNING A BLANK:

Perform a blank titration every time (it provides a more neutral starting point for the real titration) and the chance of batch failure will be greatly reduced

>>THE END<<

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