Electrogravimetric determination of lead as lead dioxide

Electrogravimetric determination of lead as lead dioxide

SHORT COMMUNICATIONS 395 est tel qu’il permet de le lager dans le compartiment des cuves de la plupart des spectrophotom&res (Cary Modeie I 1-50 et ...

200KB Sizes 0 Downloads 10 Views

SHORT COMMUNICATIONS

395

est tel qu’il permet de le lager dans le compartiment des cuves de la plupart des spectrophotom&res (Cary Modeie I 1-50 et Zeiss PMQ I I par exemple). Lc dispositif ainsi realis& est repr&cntt5 sur la Fig. I*. 11 comporte une cuvc de IO cm d’epaisseur, de capacite 30 ml et une ampoule de capacitC environ 30 ml. Le volume de l’ampoule peut &re reduit ou augmente selon la capacite de la cuvc ou selon le volume total de reactif B ajouter. La houcle C pcut comportcr un tube en plastique ou etre entierement en verre; dans ce dernier cas tile scra plus difficile zt ajuster sur les rodages de la cuve par suite cle sa rigidit& La solution& titrerestintroduitcparl’ouverturcnlenagCegceteffet dansl’ampouleI3; cllc s’~coulc ensuitc dans la cuvc ..A.Le reactif cst ajoutd en utilisant la m8me technique et l’on pro&de h un lent mouvcment d’oscillation pendant lequel le licluidc passe de la cuve A dans l’ampoule 13 en cmpruntant la boucle C. Apr&s homogeneisation on fait rcntrcr ZLnouveau la solution dans la cuve et on rep&c cc processus 3 B 4 fois avant de faire la mesure colorimetrique. On proc&de h une nouvelle addition de reactif et on applicluc la mi\mc technique avant la meSure suivante.

Unc deuxieme entrtSc pcut &rc ~~~entuellement pr&vue sur l’ampoulc mcttrc l’introduction tlu rCactif sous atmosphere incrtc. NOW rcmcrcions

M. C~or~rs pour l’execution

B afin de pcr-

de la partic on vcrre du clispositif.

Y. LE DUIGOU

Ettvatant,

Bttrcatt Ce*ttvnl de Mcsttres Gccl (i~clgiyttc)

Ntrclt!uivc?s,

Electragravimetric

determination

A. BRijCK

of lead as lead dioxide

l’rctmptccl by a suggestion of LXNGANIE~, we ltave carried out an clectrogravimctrit determination of lead by depositing it as lead dioxide which was then weighed under water to circumvent the necessity of drying.

ICnown amounts of reagent-grade lead, in the neighborhood of 40 mg were dissolved in 15 ml of G M nitric acid. The solution was diluted to about xoo ml and one ml of z 1M sulfuric acid added to retard flaking of lead dioxide at the anode; IO ml of 0.1 M copper sulfate was added to prevent deposition of lead at the cathode. The depositions AIral. CXinr. Acta, 3 I (196q) 395-396

SNORT

396

COMEfUNtCATOKS

wcrc performed at go” for 20-30 min at I A with platinum gauze electrodes. At the end of the electrolysis the anode coated with lead dioxide was washed in distilled water and hung in a container of distilled water. A platform was constructed to support this container above, and without touching, one pan of an analytical balance. The platinum wire used to hang’ the electrode in solution was marked so that on each successive wci&iw the liquid level wits the same, i.e., the clcctrade and wire were submerged to the same depth for reproducibility. The water temperature was measured and the [email protected] performed in the usual manner. The elcctrodc was removed, cleaned in nitric acid-hydrogen peroxide mixture and rcwci&ed. The diflcrcncc in weights after ;L correction for buoyancy effects gave the weight of lead dioxide. c~~cltt~tt~~~ IT = buoyant force, Q = density Where W = true weight, Iy’ = apparent wei&t, of water, 3 = density of Ic:~l dioxide, XIC~ V = volume of lend dioxide = volume of water diq3lacet1, then obviously :

The results of several tests ;Lrc shown in Table I. Although these results arc quite as good as those reported by SCHI~NK AND L)ELANO”, there is a 3-s-fold ving in time, due to both shorter time of electrolysis and to circumventing necessity of drying.

-.._ I’b

.,_..._..... .. _._-._. _-

..._._ .-- ,..__-._-ktfwt

(w) --...-_-.___.41.0

- -_.__

(WY)

-_..

_..._

40.7

43.8 37.8

39.8 53.7 _-- - ._._.

I~ct~if~lif~n

Pilfool~r& ..-.__..

44*0 38.0

_.

not snthe

39.6 53.9 . ..___.__-_ ,,.

(Wd -.. ._..__-

-0.3 -I*o.z -j- 0.2

--0:2 -}-#.;I .._. ..__.

J3esides saving time this procedure also avoids undesirable chawes in the composition of the deposits with the result that the theoretical grnvimctric factor rather than the empirical factor commonly recommended may bc used.

(Received

March

3rst,

1964) .*lrtnl.Cl1irrr.h&l,

3x (t9C4) 395-39G