The determination of the standard solution of sulfuric acid in the testing process of the nitrogen determination instrument: In a 1000 ml volumetric flask, add about 40 ml of distilled water, pipette 0.7 ml of sulfuric acid slowly into a volumetric flask, dilute to the mark with water, and shake it evenly. When preparing sulfuric acid standard solution, it should be as accurate as possible according to the provisions in GB/T19227-2008. Because the formulation concentration is high, the titration is small, but the operation error and reading error in the intangible will also increase, which affects the accuracy of the experiment. If the prepared concentration is low, although the operation error and reading error can be reduced, the large amount of titrants makes the volume of the receiving liquid too large, the determination of the end point is not accurate enough, the final result is affected, and the cost of the experiment is increased.
The calibration of the standard solution is very important. When the indicator is calibrated with methyl orange for the sulfuric acid solution, the end point is not good, because the color change is not acute. This should be noted at the time of calibration: 1 Accurately weigh and dry 0.02g of anhydrous sodium carbonate, and fully dissolve in 55ml of distilled water. Be sure to add 2.5 drops of methyl orange indicator until the solution is bright yellow, because the indicator plus or less will not be bright yellow. 2 too little indicator, the end color is not obvious, easy to make excessive titration of sulfuric acid solution; excessive indicator, the endpoint color is a bit purple. 3 When titrating, try not to calibrate in poor light or in the evening, because one-side natural light is the light source, can achieve the best titration effect. 4 In order to make the color more easily discernible, a few pages of filter paper can be added under the conical flask to make the color of the solution more obvious and easier to determine the end point.
In the determination process of the nitrogen determination instrument, we need to pay attention to the details. There is a slight oversight that will lead to an error in the results. We must always operate in accordance with the provisions of the national standard, but also on the basis of the national standard, sum up experience, improve the actual operation of the experiment and accuracy.
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