[scheikunde] bepaling van nitraten

[Pepito]

Hallo

Ik moet een nitraatbepaling doen van kunstmeststoffen ik heb dit ook gedaan maar ik weet niet hoe ik de percentage moet berekenen. Mijn titraties vindt u hieronder. Kan iemand mij helpen alvast dank
11.3 Berekening percentage bepaling van nitraten
Soorten titratie Omslagpunt (resultaat)
De werkelijke titratie (a) 5,6 ml
De blanco titratie (b) 5,7 ml


bron:
Discussion. Nitrates are reduced to ammonia by means of aluminium, zinc or,
most conveniently, by Devarda's alloy (50 per cent Cu, 45 per cent AI,
5 per cent Zn) in strongly alkaline solution:
3NO;- + 8AI+ 50H - + 2H zO = 8AIOz+ 3NH 3
The ammonia is distilled into excess of standard acid as in Section 10.35.
Nitrites are similarly reduced, and must be allowed for if nitrate alone is to
be determined.
Procedure. Weigh out accurately about 1.0 g of the nitrate. Dissolve it in water
and transfer the solution quantitatively to the distillation flask of Fig. 10.10.
Dilute to about 240 mL. Add 3 g of pure, finely divided Devarda's alloy (it
should all pass a 20 mesh sieve). Fit up the apparatus completely and place
75-100 mL standard 0.2M hydrochloric acid in the receiver (500 mL Pyrex
conical flask). Introduce 10 mL of20 per cent (0.5M) sodium hydroxide solution
through the funnel, and immediately close the trap. Warm gently to start the
reaction, and allow the apparatus to stand for an hour, by which time the
evolution of hydrogen should have practically ceased and the reduction of nitrate
to ammonia be complete. Then boil the liquid gently and continue the distillation
until 40-50 mL of liquid remain in the distillation flask. Open the tap before
removing the flame. Wash the condenser with a little distilled water, and titrate
the contents of the receiver plus the washings with standard O.2M sodium
hydroxide, using methyl red as indicator. Repeat the determination. For very
accurate work, it is recommended that a blank test be carried out with distilled
water.
1mL 1M HCI == 0.06201 g NO;-

[ArcherBarry]

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