10.9 nh lng nitrogen trong hp cht hu c

 

Nitrogen trong hp cht hu c c nh lng di dng amoniac trong amoni sulfat thu c khi v c ho cc hp cht hu c c cha nitrogen vi acid sulfuric.

Dng c

B dng c nh lng nitrogen c th c ch to nguyn b chuyn dng ct amoniac hoc c lp ghp t cc dng c thu tinh cn thit vi nhau sao cho m bo cc b phn v yu cu nh Hnh 10.9. Cc phn bng cao su ca thit b nn c x l bng cch un si 10 - 30 pht trong dung dch natri hydroxyd 1 M (TT), tip theo 30 - 60 pht trong nc, cui cng ra li bng nc trc khi dng.

A. Bnh Kjeldahl v c ho mu th v thc hin phn ng.

B. Bnh cu cung cp hi nc.

C. Phn thu hi hi.

D. Phu cp nc vo bnh B.

E. ng dn hi nc t bnh B sang bnh phn ng A.

F. Phu cp dung dch kim vo bnh phn ng A.

G. ng ni bng cao su c kp kha.

H. L nh c ng knh bng ng knh ng cp hi.

J. ng sinh hn.

K. Bnh hng dch ct c.

Ghi ch: n v o ghi trong hnh tnh bng milimet (mm).

Cch tin hnh

Nu chuyn lun ring khng c ch dn g c bit th tin hnh nh sau:

Phng php 1

a. V c ho

Ly chnh xc mt lng mu th c cha khong 5 mg nitrogen cho vo bnh Kjeldahl A, thm 1 g hn hp kali sulfat khan (TT) (hoc natri sulfat khan) v ng sulfat (TT) (t l 10:1) c tn nh, 7 ml acid sulfuric m c (TT) v vi vin bi thu tinh. y bnh bng mt phu c cung di. t bnh nghing 450 trn ngn la nh hn hp nng ln t t ri tng dn nhit ti khi si v tip tc un ti khi cht lng trong bnh c mu lc ti v khng cn nhng m en ca cht ho than trn thnh bnh. Nu cht lng trong bnh cha chuyn sang mu lc ti, c th thm 1 - 2 ml dung dch hydrogen peroxyd 100 tt (TT) khi ngui v un tip n khi thu c mu ny. un thm 30 pht na, ngui.

b. Chun b ct

Thm 20 ml nc ct vo bnh Kjeldahl v c ho, ngui tr li ri lp bnh ny vo b dng c ct c lm sch trc bng cch cho hi nc chy qua. Nu b dng c ct amoniac c bnh phn ng A gn lin th dng 20 ml nc ct chuyn hn hp t bnh Kjeldahl vo bnh phn ng.

Cho nc ct vo khong 2/3 bnh cp hi nc B, thm vi git acid sulfuric (TT) acid ho chng s thm nhp ca amoniac t khng kh.

Ly chnh xc 30,0 ml dung dch acid sulfuric 0,02 N (C) v 2 git dung dch hn hp methyl (TT) cho vo bnh hng K.

Lp ni cc b phn vi nhau nh hnh v sao cho to thnh mt h thng kn, u cui ca ng sinh hn thu dch ct c phi ngp su trong dung dch ca bnh hng K.

c. Tin hnh ct

Khi vic chun b ct hon tt, cho nc lnh chy qua ng sinh hn v bt u un nc trong bnh B. Khi nc si th cho vo bnh phn ng A qua phu F tng t mt 30 ml dung dch natri hydroxyd 40 % (TT) ( ht lng kim ny vo phu F v dng kp G iu chnh cho dung dch kim chy xung t t, khi xong kho cht kp li). Tip tc ct n khi hng c khong 100 ml dch ct. H thp bnh hng v ra u sinh hn vi mt t nc ct.

d. Chun

Chun acid sulfuric tha trong bnh hng dch ct bng dung dch natri hydroxyd 0,02N(C) ti khi chuyn sang mu vng, ghi s ml dung dch natri hydroxyd 0,02 N (C) dng (a ml).

Tin hnh song song mt mu trng theo trnh t trn. Ghi s ml dung dch natri hydroxyd 0,02 N dng (b ml).

Tnh kt qu: Lng nitrogen trong mu th (X) tnh bng gam theo cng thc:

 

X = (b - a) x 0,00028

Phng php 2

p dng cho mu th c ln nitrat v nitrit.

Tin hnh tng t nh phng php 1 nhng giai on v c ho cn tin hnh loi tr nh hng ca nitrat v nitrit nh sau:

Sau khi cho mu th vo bnh Kjeldahl A, thm 10 ml acid sulfuric (TT) ho tan 0,4 g acid salicylic (TT), lc u v yn 30 pht (thnh thong lc u). Thm 2 g natri thiosulfat (TT), lc u, thm 200 mg bt ng sulfat khan (TT) ri tin hnh v c ho ging nh phng php 1 bt u t on "t bnh nghing 450.. "

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hnh10.9: Dng c nh lng nitrogen