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To Estimate the Purity of Commercial Nitrite

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Introduction

Date: 9/9/10 Experiment No.: 1 Title: To Estimate the Purity of Commercial Nitrite Object: The purpose of this experiment is to check the purity of commercial nitrite by titration. Theory: Sodium nitrite (commercial nitrite) solution is oxidized by potassium permanganate to nitrate: 2MnO4- + 6H+ + 5NO2- --> 2Mn2+ 5NO3- +3H2O As potassium permanganate itself changes colour in this reaction, so no indicator is required. However, once sodium nitrite is acidified, nitrous acid will form and decompose (*). Thus, sodium nitrite is placed in burette and added to acidified potassium permanganate. *2NaNO2 + H2SO4 -->Na2SO4 + 2HNO2 3HNO2-->HNO3 + H2O + 2NO Experimental procedure: 1. Around ( (should be a little more for the impurity)) 0.90g sodium nitrite powder was transferred and weighed to the nearest 0.01g in a weighting bottle. ...read more.

Middle

Data Trial 1st 2nd 3rd Initial reading (cm3) 0.20 0.00 0.06 12.34 Final reading (cm3) 25.20 25.00 25.08 37.40 Titre(cm3) 25.00 25.00 25.02 25.06 Mean titre: Calculation: Mol of titre used: As only 25.02cm3 titre was used for titration, mol of the total 250cm3 sodium nitrite solution: Thus, there is pure sodium nitrite: Finally, the purity of the commercial nitrite: Result: The purity of the commercial nitrite is 95.8% Discussion: The purity was found. There was just a small difference between the reference answer (94%) and the answer calculated. The 3rd time reading was larger than the previous readings due to the slow reaction of this experiment. Thus more sodium nitrite solution was added and might affect the result. ...read more.

Conclusion

When HNO3 is added to KMnO4, NO2 is formed which is toxic. 4. In weakly acidic, weakly alkaline and neutral medium, KMnO4 reduces to form the brown solid MnO2 instead of Mn2+. Write the equation for this reduction. MnO4 + 4H+ + 4e- -->MnO2 +2H2O 5. Explain why neutral KMnO4 (aq) is seldom used in redox titration. It is because the colour change is not significant, and so it is hard to judge the end point. 6. Suggest one advantage and one disadvantage of using acidified KMnO4 in redox titration. The advantage of using acidified KMnO4 in redox titration is the great colour change and so it can be indicator itself. The disadvantage of it is that it cannot react with compound containing chloride ion or high concentration acid. Conclusion: After the experiment and calculation, the purity found is 95.8%. ...read more.

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