Lab Report 9 - About redox titration PDF

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About redox titration...

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Redox Titration Introduction: Redox titration is the type of titration based on redox reaction between the analyte and titrant. Redox titration includes oxidation half reactions and reduction half reactions. Oxidation reduction reactions involve transfer of electrons. In this experiment, both oxidation half reactions and reduction half reactions are found. The purpose of the experiment was to observe the redox titration of potassium permanganate and sodium oxalate in an acidic solution and to determine the average molarity of the potassium permanganate by titrating sodium oxalate solution of known molarity. It was hypothesized that the potassium permanganate neutralized sodium oxalate completely and molarity of potassium permanganate could be determined by titration.

Experimental: For this experiment, burette, beaker, graduated cylinder, stirrer, dropper, funnel, sodium oxalate and potassium permanganate were used. At first the burette was filled with potassium permanganate up to zero level. Approximately 0.25 g of sodium oxalate was measured and kept inside the beaker to make aqueous solution of sodium oxalate. Again about 3 mL of 3M sulfuric acid was measured in graduated cylinder and mixed with the solution of sodium oxalate to make acidic solution. The whole solution was placed above stirrer to mix the solution completely. The burette filled with potassium permanganate was placed above solution so that potassium permanganate could drop to the solution. At each titration, single drop of potassium permanganate was added at a time to the solution of beaker. At first addition of potassium permanganate to the solution, the solution was left for a while to react completely with acidic sodium oxalate solution until the pink color changed to purplish color. After some time, another

drop of potassium permanganate from burette was dissolve in the solution. After 5 mL of potassium permanganate, the titration was done a little fast than previous. The potassium permanganate was added to the solution until the solution stayed purple. The same experiment was repeated for 4 times with different measurements of sodium oxalate and molarity was calculated at each experiment through titration. After completion of the experiment, the burette was rinsed with water and solution was disposed to the waste. The burette was neutralized by the acidic solution of sodium oxalate and then was cleaned with water.

Result: The molarity of the potassium permanganate was calculated at each time through titration with acidic solution of acidic oxalate. The data was collected for each experiment and data were included in the table. Trial

Mass of sodium

Volume of H2SO4

Volume of KMnO4

1 2 3 4

oxalate (g) 0.27g 0.25g 0.25g 0.26g

(mL) 3.0mL 3.0mL 3.0mL 3.0mL

(mL) 43 mL 36 mL 40 mL 40.2 mL

Oxidation- half reactions: MnO4- + 8H+ + 5e-→ Mn2+ + 4H2O ] ×2 Reduction- half reaction: (COO-)2 – 2e-→ 2CO2 ] ×5 Redox reaction: 2MnO4- + 16H++ 5(COO-)2-→ 2Mn2+ + 8H2O + 10CO2 2KMnO4- + 5Na2C2O4 + 8H2SO4→ K2SO4 + 2MnSO4 + 10CO2 + 5Na2SO4 + 8H2O

From above equation, it was found the relation between moles of potassium permanganate that can neutralized moles of acidic sodium oxalate. 2 mol of potassium permanganate = 5 mol of acidic sodium oxalate For 1st trial, the mass of sodium oxalate was 0.27 g, the moles of sodium oxalate was calculated which is mentioned below,

Here moles of sodium oxalate =

=

mass of sodium oxalate molar mass of sodium oxalate 0.27 g 134 g /mol

= 0.002 mol Now, the molarity of potassium permanganate could be calculated by titration, which is given by,

43 mL KMnO4 =0.002mol Na2C2O4×

1 5 mol KMnO 4 1000 mL × × 2 mol Na 2C 2 O 4 43 mL KMnO 4 1 L KMnO 4

= 0.0186 M KMnO4 For 2nd trial, the mass of sodium oxalate is 0.25g, the moles of sodium oxalate could be obtained as given below:

Moles of sodium oxalate=

mass of sodium oxalate molar mass of sodium oxalate

=

0.25 g 134 g /mol

= 0.00187 mol Now, the molarity of potassium permanganate could be calculated by titration, which is given by,

36 mL KMnO4 =0.00187mol Na2C2O4×

1 5 mol KMnO 4 × 2 mol Na 2C 2 O 4 1 L KMnO 4

×

1000 mL 36 mL KMnO 4 = 0.129861 M KMnO4 For 3rd trial, the mass of sodium oxalate is 0.25g, the moles of sodium oxalate could be obtained as given below:

Moles of sodium oxalate=

mass of sodium oxalate molar mass of sodium oxalate

=

0.25 g 134 g /mol

= 0.00187 mol Now, the molarity of potassium permanganate could be calculated by titration, which is given by,

40 mL KMnO4 =0.00187mol Na2C2O4×

1 5 mol KMnO 4 × 1 L KMnO 4 2 mol Na 2C 2 O 4

×

1000 mL 40 mL KMnO 4 = 0.116875M KMnO4 For 4th trial, the mass of sodium oxalate is 0.26g, the moles of sodium oxalate could be obtained as given below:

Moles of sodium oxalate=

mass of sodium oxalate molar mass of sodium oxalate

=

0.26 g 134 g /mol

= 0.00194 mol Now, the molarity of potassium permanganate could be calculated by titration which is given by,

40.2 mL KMnO4 =0.00194mol Na2C2O4×

1 5 mol KMnO 4 × × 2 mol Na 2C 2 O 4 1 L KMnO 4

1000 mL 40.2 mL KMnO 4 = 0.12067 M KMnO4 Hence, the average molarity of KMnO4 could be determined which is given below,

Average molarity of KMnO4=

0.0186 + 0.12986 +0.116875 +0.12067 4

= 0.0965 M KMnO4 Hence, the average molarity of potassium permanganate was found to be 0.0965 M.

Conclusion: The molarity of potassium permanganate for each trial was calculated and the average molarity of potassium permanganate was found to be 0.0965M. the experiment helps to find the molarity of solution by titration. The experiment also helps to know the concept of redox reaction and titration. The possible reasons of error in the experiment due to inappropriate amount of chemicals, contaminated burette and measurements. These errors could be reduced by taking appropriate amount of chemicals and using clean vessel or burette. The experiment could be used in future to determine the molarity of other compounds through titration of redox reactions.

For this experiment, around 0.25 g of sodium oxalate was measured and aqueous solution of sodium oxalate was prepared. Around 3 mL of 3M sulfuric acid was added to the solution to make the solution acidic. Then, the burette filled with potassium permanganate was allowed to titrate with acidic sodium oxalate. The beaker with acidic sodium oxalate was placed above stirrer and a single drop of potassium permanganate was added to the solution at a time. After 5 mL of potassium permanganate, titration was done in a fast rate. After titration, the purple color of the potassium permanganate was found colorless and complete neutralization was obtained....