Лаборатория иши №5

LABORATORY WORK 4


PRODUCTION OF NITROGEN FERTILIZERS AND DETERMINATION OF NITROGEN CONTENT IN THE FORMAL METHOD


Purpose of work:Determination of nitrogen content in nitrogen fertilizers by formaldehyde method.
Required equipment and reagents:glass 200ml, magnetic stirrer, micro burette, formalin 40%, indicator phenolphtholein, ammonium nitrate salt,
Since nitrogen, which is an inorganic and organic substance, is of great importance, its determination is an important analytical task. To determine nitrogen, it is converted to ammonia. To do this, ammonium salts are boiled with alkali, nitrate and nitrites are returned with a Devard alloy containing 45% Al, 5% Zn and 50% Cu, nitrogenous organic compounds are heated with concentrated H2SO4 and the resulting ammonium hydrosulfate alkali (Keldal method) decomposes with.
There are a number of methods for determining ammonia, some of which we will consider
`The first method. When a large amount of formaldehyde is added to a solution of ammonium salts, the reaction results in the formation of an equivalent amount of hydrogen ion and a heterocyclic compound - urotropin.
4NH4 ++ 6HCHO = 4H ++ (CH2) 6H4 + 6H2O.
The amount of nitrogen is determined by titrating the resulting colored hydrogen ion with a standard solution of sodium hydroxide. Due to the fact that urotropin is dyed with a weak basic property (Kb = l, 4,10-9), the pH of the solution at the equivalent point is 9. It is therefore advisable to use phenolphthalein as an indicator.
Procedure for analysis.1.5-3.0 g of ammonium salt (depending on the nature of the salt) is added to the beaker and weighed on a technical scale. The beech is then weighed accurately on an analytical balance with salt. After placing the salt in the beaker in a 250 ml volumetric flask using a dry funnel, the beaker is weighed again on an analytical balance with a load of salt. The difference in masses is equal to the mass of the salt obtained. Once the salt in the funnel is completely transferred to the measuring flask with distilled water, it is completely dissolved. Once the salt has dissolved, water is added to the mark of the flask and the resulting solution is stirred vigorously. Pipette 5 ml of 40% formaldehyde solution into the titration flask. Add 3-4 drops of phenolphthalein solution to the resulting solution and titrate with 0.1 N NaOH solution until a light red color appears. Then 25.00 ml of ammonium salt solution is pipetted into this solution. mixed and titrated with a standard solution of NaOH after 3–4 min for 30 s until a light red color is formed that does not disappear. Repeat the titration 3-4 times to obtain the average value of the titrant