To Estimate the Purity of Commercial Nitrite

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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.
  2. The sodium nitrite powder was dissolved in distilled water in volumetric flask of 250cm3 where the molarity was about 0.05M.
  3. 25cm3 0.02M potassium permanganate solution was pipette into a conical flask, 15cm3 dilute sulphuric acid was added for acidification.
  4. Sodium nitrite solution was transferred to burette for titration.
  5. The initial burette reading was taken.
  6. Sodium nitrite solution was slowly added to the acidified permanganate solution with continual swirling until the colour of the permanganate solution was just become colourless.
  7. Final burette reading was taken.
  8. The steps above were repeated for at least 3 times to obtain more results.
  9. Calculation should be done.
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The permanganate solution changed from purple to colourless under the reaction.


Mean titre:


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%


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 ...

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