How to determine amount of Nitrite
Nitrite
Sodium nitrite is a good steel corrosion inhibitor which can be used in open recirculating cooling systems. However, due to problems with nitrifying bacteria which oxidize it to nigrate, it is most often applied in closed systems. While nitrites are sometimes regarded as reducing agents, it is their oxidizing properties that create inhibition by promoting the formation of a passive film on the steel surface.
View our most popular handbook on Water Treatment chemicals
To establish a protective iron oxide film, it is sometimes necessary to feed nitrite initially at a greater concentration than normally required. The feedrate can be reduced to normal once the protective film has been established. Both oxidizing and reducing agents will destroy nitrite. These decomposition problems and the problem of bacterial-induced oxidation make it difficult to maintain effective nitrite concentrations in open circulating systems without using excessive feedrates. However, where nitrite concentrations can be continuously maintained at an effective level, and especially in closed systems, satisfactory protection of ferrous metals is obtained.
Nitrite Direct Titration Method (0-230 ppm) Theory of Test
This test is based on the determination of the nitrite content of a sample by titration in an acid medium with a standard oxidizing agent, potassium permanganate. Nitrite is quantitatively oxidized to nitrate. The permanganate titrant is purple, but forms a colorless product in the reaction with nitrate. Thus, the persistence of a definite pink color for one minute, which indicates excess permanganate, is taken as the endpoint.
Chemicals Required
Potassium Permanganate, 0.1N
Sulfuric Acid, 5%
Preparation of Titrating Solution
The titrating solution, 0.01N potassium permanganate, has limited stability and must be prepared fresh each month. To prepare, pipet 50 ml of 0.1N potassium permanganate into a 500 ml volumetric flask and dilute to 500 ml with distilled water. Protect the titrating solution from light by storing in amber colored bottles.
Procedure for Test
Measure a 10-ml sample into the graduate and cool to room temperature. Transfer to the casserole; measure 3-ml of the 5 per cent sulfuric acid into the 10-ml graduate, and add to the sample in the casserole. Use a 100-watt bulb directly over the casserole for illumination. Add the standard 0.01N potassium permanganate from the buret, drop by drop to the sample in the casserole stirring constantly until a pink color starts to persist.
At this point of the determination, add the permanganate 1.0-ml at a time with constant stirring. Continue to add the permanganate at the rate of 1.0 ml until a definite pink color persists for one minute. The time interval of one minute should be measured with a stopwatch.
Calculation of Results
FORMULA:
ppm nitrite as NO2= Ml 0.01N of potassium permanganate x 1000/ml sample
Using a 10 ml sample, nitrite in parts per million as NO2 is equal to the ml of 0.01N potassium permanganate multiplied by 23.
Limitations of Test
This method is rapid and adaptable for control purposes where nitrite is used as a corrosion inhibitor. It is affected by any oxidizable substances in the sample such as organic matter, sulfides, hydrogen sulfide and mercaptans. If present, these substances will interfere by reacting with the titrating, potassium permanganate, yielding an erroneously high nitrite concentration.
|
Apparatus Required |
||
|
Buret, automatic, 25 ml |
- |
1 |
|
Casserole, 210 ml |
- |
1 |
|
Cylinder, graduated, 10 ml |
- |
1 |
|
Pipet, 50 ml |
- |
1 |
|
Stirring rod, |
- |
1 |
|
Timing device |
- |
1 |
|
Volumetric flask, 500 ml. |
- |
1 |
For more information, kindly mail us at: mail@rxmarine.com
Product: