REDOX Titration



Virtual REDOX Titration

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PROBLEM:

The purpose of this experiment is to determine the number of grams of Fe in a sample through titration with potassium permanganate in an acidic solution.

BACKGROUND: Potassium permanganate, KMnO4, is widely used as an oxidizing agent in volumetric analysis in an acidic solution. MnO4-1 ion undergoes reduction to Mn+2 as shown in the following equation.

8H+ (aq) + MnO4-1 (aq) + 5e-1 ( Mn+2 (aq) + 4H2O (l)

In the present experiment you will take a sample containing iron, add acid to dissolve it [thereby converting all the iron to iron(II)], then use a solution containing permanganate ion, MnO4-, to oxidize this Fe2+ to Fe3+ ion. The percent of iron in the sample will be calculated from the amount of permanganate needed to oxidize fully all the Fe2+ ions.

A solution of permanganate ion in sulfuric acid efficiently oxidizes Fe2+ to Fe3+

The permanganate ion acts as its own indicator, as MnO4- is highly colored while Mn2+ is essentially colorless.

PROCEDURE:

1. Select the reaction where the oxidizing agent is KMnO4 and the reducing agent is Fe+2.

2. Push the slider up to fill the buret with KMnO4.

3. Record the molarity of KMnO4. Record the volume of Fe+2 in the Erlenmeyer flask.

4. Add a small amount of KMnO4 from the buret to the Erlenmeyer flask by pushing the slider up. The liquid will enter the flask when you release the slider. Continue to add a small amount of KMnO4 to the flask at a time. When a temporary pink color is seen in the flask start to add KMnO4 by using the dropwise button.

5. Continue to add KMnO4 to the Fe+2 until a permanent pink color is obtained.

6. Record the volume of KMnO4 needed to titrate the Fe+2.

7. Calculate the molarity of the Fe+2 and enter it into the appropriate space. Check to see if it is correct.

If it is not correct repeat the titration until your molarity is correct.

WARNING: RESETTING THE EXPERIMENT WILL GIVE YOU A DIFFERENT SAMPLE OF KMNO4, WITH A DIFFERENT MOLARITY.

DATA/RESULTS

| |Trial 1 |

|Molarity of KMnO4 | |

|Volume of Fe+2 | |

|Volume of KMnO4 needed to titrate | |

|Molarity of Fe+2 | |

|Mole ratio Fe/MnO4-1 from bal. Equation | |

|Moles Fe in sample | |

|Grams Fe in sample | |

Write the balanced redox reaction below:

CALCULATIONS: Show set up and all work. Box your answer.

A. Determine the number of moles of permanganate ion consumed.

B. Using the mole ratio of the balanced equation, determine the number of moles of Fe+2 ions that were reacted with the permanganate ion consumed.

C. Determine the number of grams of Fe+2 that reacted.

POST LAB QUESTIONS

A. Examine the five reactions shown below and identify those that can be classified as oxidation- reduction. If not redox, determine the type of reaction.

1. 2H3PO4 + 3 Ca(OH)2 ( Ca3(PO4)2 + 6H2O

2. 2Cr + 3Cl2 ( 2CrCl3

3. C6H12O6 + 6O2 ( 6CO2 + 6H2O

4. Na2CO3 ( Na2O + CO2

5. 2VO+2 + Zn + 4H+ ( 2V+3 + Zn+2 + 2H2O

The usefulness of metals in structural applications depends on their physical and chemical properties. Corrosion is the oxidation of metals and is a common failing point for a metal structure.

| |Cu(NO3)2 |Mg(NO3)2 |Zn(NO3)2 |AgNO3 |

|Cu(s) | |No reaction |No reaction |Silver crystals form on Cu(s) surface; |

| | | | |Solution turns green |

|Mg(s) |Dark precipitate forms. Solution | |Solution bubbles and dark |Large amount of flaky precipitate forms; |

| |bubbles, turns green/gray | |precipitate forms |solution turns dark gray |

|Zn(s) |Dark precipitate forms, solution slowly|No reaction | |Large amount of flaky gray precipitate |

| |turns green | | |forms; solution turns gray |

B. Examine the observations above for the metals Cu, Mg and Zn. Identify the metal that is most susceptible to oxidation (corrosion). Identify the metal that is most resistant to oxidation.

C. Because silver metal is expensive, it is not used in the tests shown above. Based on the reactions of Cu, Mg and Zn with silver nitrate, explain why is was not necessary to test silver metal in order to determine its reactivity.

D. Student performs a titration of Ferrous ammonium sulfate with Potassium permanganate. She calculates that 0.002634 moles of Fe2+ reacted with the permanganate ion. What is the percent Fe+2 in the 1.235 gram sample of ferrous ammonium sulfate. The molar mass of Fe(NH4)2(SO4)2.6H2O is 392.2 g.Show work, box answer.

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