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Heterometric micro-determination of uranium (VI) by precipitation with ferrous cyanide
VOL.
84
11
MICliO-Dl~‘l’J~R~lINA’TION OF URANIUM(V1) l’RECIPI1‘A’I’ION WITH FJ
I-I~‘l‘J’:12OiLI15-~IiIC
(1954)
BY
The lzecipitstion of uranium (VI) with l>otassium fcrrocyanide and its gravimetric determination as UO,[Fe(CN),,~ is bound up with considerable difficulties. The dark red precipitate obtained is of very fine colloidal character and therefore the gravimetric method would bc one of the undergoes adsorption. Although most scnsitivc, because of the difficulties involved, the intensity of the colour obtained is used for the determination instead of a gravimetric &termination. The following hctcromctric method is based on the photometric determination of the optical density of the +vcci$italed UO,CI;e(CN),]. In this work it was our purpose to make use of all the advantages presented by the gravimetric determination of uranium, but to avoid separation and weighing. arc encountered due As the following material shows, no difficulties whatsoever is not sefinvntcd fvonr to possible rtdsov#ion ~71crtomenu, so Zoq as the fi,rzcipitate flu solution. This fcaturc makes the heteromctric method especially useful and easy to carry out. M’c prcscnt hcrc only the mtaZyytica2 aspects of the results obtained. EXPERISIESTAL
All details concerning the Hctcromctcr and the hcteromctric titrations are given clscwhcrclle. The chemicals used wcrc all Baker analyscd c.11. reagents. A red filter was used in all the following cspcriments in order to avoid colour interrercncc. RESULTS
A sclcction of results arc compiled in Table I and Figs. I and 2. The table gives the numerical values of the different csycriments, while the curves show the course of titration of the corresponding espcrimcnts. The composition of each cspcriment is seen in Table I. I3y the dropwise addition of potassium ferrous References p. 87.
VOL.
11
(1954)
HETEROMETRIC
MICRODETERMINATION
OF
URANIUM
85
cyanide to the solution of uranyl nitrate, we obtain in all cases without exception, a red brown @m’pitate, the optical density of which is measured. As experiment I and 3 show, under similar working conditions, we obtain the same numerical maximum density values in neutral and acidic solutions. The addition of NH,NO, (exp. 2) increases the maximum value and thcrcfore makes the measurements more sensitive. A comparison of exps. 4 and 5 shows that the titration with a more dilute ferrous cyanide solution causes some increase in the maximum density although less uranium is determined. But it must be borne in mind that even the maximum density value of the same experiment may vary somewhat with changing conditions (e.g. temperature etc.). The possible fluctuation of the maximum density value in no way impairs the accuracy of the determination, which does not dcpcnd on the numerical maximum value. For comparison, the experiments are grouped in two figures (I and 2). As can be seen, the highest maximum values
0.7
06
0.5
a4
0.3
Qd
0.1
5mt
Fig I.
6
0.0 0
3
.?
Fig.
4
5 ml
2
are obtained working in acid solution and at a high NH,NO, concentration(exps. 7 and 8). The uranium concentration can then be reduced to about one fifth of the regular concentration used. As exp. g shows, a considerable decrease of the maximum value occurs in alcoholic solutions. In the presence of very high concentrations of NH,NO,, and with low concentration of uranium (exps. 7-g), Refermtces
p. 87.
M.
86
ROBTELSKY,
TARLE _---Gcncral
--^_
-_____
Composition:
u ml
_-_-_.-.-
__--_.--
_- -_.- -_-.---_.-
__ __ _______________
UO,(NO,,), + l\,[Lic(CN),] _---.. -_.----.
(10-a)
ml
______-___
solutkn
-/-
S
ml
xn.11
---
UO,(XO:,),
Uranium in mg ml molar _..__ -_ --__ -.___-_-----.-
.__ ..-_-.
(1954)
11
I __--______._
nM
Solution
Exp.
VOL.
IIALPERN
M.
&[:;J.(N),] .1 ml molar -. ---.-
NLaxiFum
y.
dcns1ty
.--
._.-_
Error _____
4
0.004
3.81
4.0
0.00.1
o-54
4
0.004
3.8~
3.9
0.004
0.75
4
0.004
3.81
.).O
0.004
OS.54
G ml 1~11 NI-IoNO:,
4
0.002
I .gos
I.95
0.004
o-43
2-s
5
G ml lM
3
0,002
I.43
3.1
o.oo.?
0.48
3.3
G
G ml wild NT-I,NO, I 1Yll Ilk? cH,Coo1-L
3
0.002
x.43
3.0
0.002
0.gC
0
3 ml GM NI-I,KO, -f1 ml IAN CH,COOH +3 ml I-T,0
3
0.002
r-43
3-0s
0.002
0.08
1.G
-I3 ml GAf Nl-I&O, I ml IAf CH,COOIX -1-3 ml I-I,0
3
0.00
I.55
0.002
0.38
3.3
I ml rM CH,COOH -t_ 1 ml El,0 i-5 ml alcohol
3
o.ooz*)
0.2-J
0
I
0 ml l-I,0
2
3 ml rA\l NI.f,,NO,+3
3
1 ml r:lf
4
7
8 s)
ml I-I,0
CI-I,,COOI-I
f5
ml I-I,0
NMqNOR -I- I ml l-I,0
_________--____-
+
..--.--___--__
.
I
o.ooz*)
0.714
1.43
3-o
- .._--.--..-.._..__. - .---- ._..-._
0
2.5 0
_. -.-._____ _._-___ __________
*) 5o”A, alcohol
the maximum density lines arc no longer horizontal. The time rcquirccl for a complete titration shows little variation, cvcn though the uranium concentration and the other espcrimental conditions vary. Gcncrnlly, about 20 minutes are rcquirccl for each titration, at room tempcraturc. It now remains to clarify the interrclntion bctwecn the .sc?~sitivity of tlic titration and the czfxxrncy of the dctcrrnination. The numerical value of the maximum density indicates to what cstcnt an analysed solution may still bc diluted, hence it indicates the sensitivity. This dots not ncccssarily mean that the latter property is conncctcd with the highest precision. The dctemrinntion of the endpoint is easy and sure, given the following conditions : I) the reaction proceeds quickly thus giving constant galvanometer readings after a few seconds: 2) the first maximum density value remains unchanged by the addition of titrant or the changes proceed regularly. The sensitivity, on the other hand, clcpencls on the insolubility (expressed in mol.) of the compound obtained. Refc~e?zccs
p.
87.
VOL.
11
(1954)
HETEROMETRIC
MICRODETERMINATION
OF
URANIUM
87
METHOD
I-Z ml concentrated NH,NO, and a few drops of concentmtccl acetic acid (final concentration about o.xN) arc added to a water solution which contains a few mg of uranium (VI) (0.5 to 3 mg) in a volume of about IO ml. A standardized solution of about 0.002Al K,,[Fe(CN),] is added drop by drop from a microburet while the solution is stirred vigorously. The readings of the galvanomctcr arc taken when they bccomc constant. The first maximum optical density point which corresponds to the endpoint, is taken by cstrapolation from a graph (enlarged) by drawing a lint through the masima values obtained. Where the quantity of uranium is unknown, it is advisablc to make a rougll preliminary hcteromctric titration, taking only a few points, following which the final titration is made.
A mctlmcl is _prcscntcd fur the dctcrmination of uranium (VI) by a hcterometric titration with k,[Fc(CN),]. 0.5-3 rng of uranium in 10 ml solution may bc clctermined in 15-20 niinutcs. The error amounts to 0-3’:/0.
Unc nidthoclc cst pr&icntk pour la cl6tcrmination clc l’uranium (VI) au moycn de KbCFc(CN)J par titration lrdteromdtricluc. 0.5-3 ml cl’urnnium clans 10 ml dc solution peuvcnt Otre ddtcrniink cn 15-20 minutes, avec une erreur dc 0-3’j&.
Einc Mcthoclc wird gcbracht zur I3cstimmun~ von Uranium (VI) mlt I-Iilfc ciuer hcteromctrischen Titration mit elncr l&sung von IC,[L;e(CN),]. 0.5-3 mg Uranium in IO ml LOsung kiinncn 11115-20 Minutcn mit cmcr Gcnauiglteit von o-3 ‘yObcstimmt werclcn.
1 M. 2 &I.
130lrTELSKY BOBTELSl
press). 3 M. BOUTELSKS 4 M. ~OI3TELSliY ccmbre. s %I. ~~OBTELSKY o hI.
BOBTDLSXY
ANV ANI~
I. l3~~-GADDA, 13. GRAUS,
13&l.
ANI., AND
13. GHAUS, r112ctl. I. ~~AR&AIJL)A,
AND
Y.
\VELWAR~,
AND
fir.
~ISILlSIZ,
J.
SOG.
Am.
Chrlir.
/ImzL.
Anal. ilMd.
clrinr.,
(1953) 276, 382, 75 (1953) 4x72;
Chc?u. Sot.,
chilJ2.
/1ck2,
CJ
(‘953)
Clrirn. /1&a, Chign. ff
Acta, Ch,
IO
g
X03. (1953)
9 (rg53) (1954)
G87, Brg. ibid.,
168;
281,
No. 374;
(in
cl& IO
260.
Rcce~vecl December
xgth,
1953
84
11
MICliO-Dl~‘l’J~R~lINA’TION OF URANIUM(V1) l’RECIPI1‘A’I’ION WITH FJ
I-I~‘l‘J’:12OiLI15-~IiIC
(1954)
BY
The lzecipitstion of uranium (VI) with l>otassium fcrrocyanide and its gravimetric determination as UO,[Fe(CN),,~ is bound up with considerable difficulties. The dark red precipitate obtained is of very fine colloidal character and therefore the gravimetric method would bc one of the undergoes adsorption. Although most scnsitivc, because of the difficulties involved, the intensity of the colour obtained is used for the determination instead of a gravimetric &termination. The following hctcromctric method is based on the photometric determination of the optical density of the +vcci$italed UO,CI;e(CN),]. In this work it was our purpose to make use of all the advantages presented by the gravimetric determination of uranium, but to avoid separation and weighing. arc encountered due As the following material shows, no difficulties whatsoever is not sefinvntcd fvonr to possible rtdsov#ion ~71crtomenu, so Zoq as the fi,rzcipitate flu solution. This fcaturc makes the heteromctric method especially useful and easy to carry out. M’c prcscnt hcrc only the mtaZyytica2 aspects of the results obtained. EXPERISIESTAL
All details concerning the Hctcromctcr and the hcteromctric titrations are given clscwhcrclle. The chemicals used wcrc all Baker analyscd c.11. reagents. A red filter was used in all the following cspcriments in order to avoid colour interrercncc. RESULTS
A sclcction of results arc compiled in Table I and Figs. I and 2. The table gives the numerical values of the different csycriments, while the curves show the course of titration of the corresponding espcrimcnts. The composition of each cspcriment is seen in Table I. I3y the dropwise addition of potassium ferrous References p. 87.
VOL.
11
(1954)
HETEROMETRIC
MICRODETERMINATION
OF
URANIUM
85
cyanide to the solution of uranyl nitrate, we obtain in all cases without exception, a red brown @m’pitate, the optical density of which is measured. As experiment I and 3 show, under similar working conditions, we obtain the same numerical maximum density values in neutral and acidic solutions. The addition of NH,NO, (exp. 2) increases the maximum value and thcrcfore makes the measurements more sensitive. A comparison of exps. 4 and 5 shows that the titration with a more dilute ferrous cyanide solution causes some increase in the maximum density although less uranium is determined. But it must be borne in mind that even the maximum density value of the same experiment may vary somewhat with changing conditions (e.g. temperature etc.). The possible fluctuation of the maximum density value in no way impairs the accuracy of the determination, which does not dcpcnd on the numerical maximum value. For comparison, the experiments are grouped in two figures (I and 2). As can be seen, the highest maximum values
0.7
06
0.5
a4
0.3
Qd
0.1
5mt
Fig I.
6
0.0 0
3
.?
Fig.
4
5 ml
2
are obtained working in acid solution and at a high NH,NO, concentration(exps. 7 and 8). The uranium concentration can then be reduced to about one fifth of the regular concentration used. As exp. g shows, a considerable decrease of the maximum value occurs in alcoholic solutions. In the presence of very high concentrations of NH,NO,, and with low concentration of uranium (exps. 7-g), Refermtces
p. 87.
M.
86
ROBTELSKY,
TARLE _---Gcncral
--^_
-_____
Composition:
u ml
_-_-_.-.-
__--_.--
_- -_.- -_-.---_.-
__ __ _______________
UO,(NO,,), + l\,[Lic(CN),] _---.. -_.----.
(10-a)
ml
______-___
solutkn
-/-
S
ml
xn.11
---
UO,(XO:,),
Uranium in mg ml molar _..__ -_ --__ -.___-_-----.-
.__ ..-_-.
(1954)
11
I __--______._
nM
Solution
Exp.
VOL.
IIALPERN
M.
&[:;J.(N),] .1 ml molar -. ---.-
NLaxiFum
y.
dcns1ty
.--
._.-_
Error _____
4
0.004
3.81
4.0
0.00.1
o-54
4
0.004
3.8~
3.9
0.004
0.75
4
0.004
3.81
.).O
0.004
OS.54
G ml 1~11 NI-IoNO:,
4
0.002
I .gos
I.95
0.004
o-43
2-s
5
G ml lM
3
0,002
I.43
3.1
o.oo.?
0.48
3.3
G
G ml wild NT-I,NO, I 1Yll Ilk? cH,Coo1-L
3
0.002
x.43
3.0
0.002
0.gC
0
3 ml GM NI-I,KO, -f1 ml IAN CH,COOH +3 ml I-T,0
3
0.002
r-43
3-0s
0.002
0.08
1.G
-I3 ml GAf Nl-I&O, I ml IAf CH,COOIX -1-3 ml I-I,0
3
0.00
I.55
0.002
0.38
3.3
I ml rM CH,COOH -t_ 1 ml El,0 i-5 ml alcohol
3
o.ooz*)
0.2-J
0
I
0 ml l-I,0
2
3 ml rA\l NI.f,,NO,+3
3
1 ml r:lf
4
7
8 s)
ml I-I,0
CI-I,,COOI-I
f5
ml I-I,0
NMqNOR -I- I ml l-I,0
_________--____-
+
..--.--___--__
.
I
o.ooz*)
0.714
1.43
3-o
- .._--.--..-.._..__. - .---- ._..-._
0
2.5 0
_. -.-._____ _._-___ __________
*) 5o”A, alcohol
the maximum density lines arc no longer horizontal. The time rcquirccl for a complete titration shows little variation, cvcn though the uranium concentration and the other espcrimental conditions vary. Gcncrnlly, about 20 minutes are rcquirccl for each titration, at room tempcraturc. It now remains to clarify the interrclntion bctwecn the .sc?~sitivity of tlic titration and the czfxxrncy of the dctcrrnination. The numerical value of the maximum density indicates to what cstcnt an analysed solution may still bc diluted, hence it indicates the sensitivity. This dots not ncccssarily mean that the latter property is conncctcd with the highest precision. The dctemrinntion of the endpoint is easy and sure, given the following conditions : I) the reaction proceeds quickly thus giving constant galvanometer readings after a few seconds: 2) the first maximum density value remains unchanged by the addition of titrant or the changes proceed regularly. The sensitivity, on the other hand, clcpencls on the insolubility (expressed in mol.) of the compound obtained. Refc~e?zccs
p.
87.
VOL.
11
(1954)
HETEROMETRIC
MICRODETERMINATION
OF
URANIUM
87
METHOD
I-Z ml concentrated NH,NO, and a few drops of concentmtccl acetic acid (final concentration about o.xN) arc added to a water solution which contains a few mg of uranium (VI) (0.5 to 3 mg) in a volume of about IO ml. A standardized solution of about 0.002Al K,,[Fe(CN),] is added drop by drop from a microburet while the solution is stirred vigorously. The readings of the galvanomctcr arc taken when they bccomc constant. The first maximum optical density point which corresponds to the endpoint, is taken by cstrapolation from a graph (enlarged) by drawing a lint through the masima values obtained. Where the quantity of uranium is unknown, it is advisablc to make a rougll preliminary hcteromctric titration, taking only a few points, following which the final titration is made.
A mctlmcl is _prcscntcd fur the dctcrmination of uranium (VI) by a hcterometric titration with k,[Fc(CN),]. 0.5-3 rng of uranium in 10 ml solution may bc clctermined in 15-20 niinutcs. The error amounts to 0-3’:/0.
Unc nidthoclc cst pr&icntk pour la cl6tcrmination clc l’uranium (VI) au moycn de KbCFc(CN)J par titration lrdteromdtricluc. 0.5-3 ml cl’urnnium clans 10 ml dc solution peuvcnt Otre ddtcrniink cn 15-20 minutes, avec une erreur dc 0-3’j&.
Einc Mcthoclc wird gcbracht zur I3cstimmun~ von Uranium (VI) mlt I-Iilfc ciuer hcteromctrischen Titration mit elncr l&sung von IC,[L;e(CN),]. 0.5-3 mg Uranium in IO ml LOsung kiinncn 11115-20 Minutcn mit cmcr Gcnauiglteit von o-3 ‘yObcstimmt werclcn.
1 M. 2 &I.
130lrTELSKY BOBTELSl
press). 3 M. BOUTELSKS 4 M. ~OI3TELSliY ccmbre. s %I. ~~OBTELSKY o hI.
BOBTDLSXY
ANV ANI~
I. l3~~-GADDA, 13. GRAUS,
13&l.
ANI., AND
13. GHAUS, r112ctl. I. ~~AR&AIJL)A,
AND
Y.
\VELWAR~,
AND
fir.
~ISILlSIZ,
J.
SOG.
Am.
Chrlir.
/ImzL.
Anal. ilMd.
clrinr.,
(1953) 276, 382, 75 (1953) 4x72;
Chc?u. Sot.,
chilJ2.
/1ck2,
CJ
(‘953)
Clrirn. /1&a, Chign. ff
Acta, Ch,
IO
g
X03. (1953)
9 (rg53) (1954)
G87, Brg. ibid.,
168;
281,
No. 374;
(in
cl& IO
260.
Rcce~vecl December
xgth,
1953