A Study of the Vogel Reaction for the Determination of Cobalt.

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1949

A Study of the Vogel Reaction for the Determination of Cobalt. A Study of the Vogel Reaction for the Determination of Cobalt.

Charles Gosse De vries Louisiana State University and Agricultural & Mechanical College

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Recommended Citation Recommended Citation De vries, Charles Gosse, "A Study of the Vogel Reaction for the Determination of Cobalt." (1949). LSU Historical Dissertations and Theses. 7927. https://digitalcommons.lsu.edu/gradschool_disstheses/7927

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119-a

a studt m the vooel beactiokrat THE UEffitMXHATXGV Off CG9BAX3?

A Biufffeatlcu

Submitted to the Graduate Faculty of the Louisiana State University and

Agricultural and Mechanical College la partial fulfillment of the requirements for the degree of

Doctor of Philosophyin

The Department of Chemistry

byCharles Cosse do Fries

A.B., Vest Virginia University, 19^1 M.S., Louisiana State University, 19^6

June, 19*9

UMI Number: DP69305

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The author viahea to ea$r*ee M i aiaeere appreciation M r the lnepiretleii, airier and u i i i t m of hr. FkLXip W, Hoot, wider M w i direction this reeeareh w i porfotn A,

Sho support of the Office of BfctaX Research, IBavy Departnent, during the greater portion of this m o t lo acknowledged.

80 lo grateful to hlo rife, Laura, for Iwar enoouragomont and especially for typing the entire dissertation.

oL°\ a u Ql L i

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O11 3 4 7 (J2i

TABUS CP CGHTKHTS

I IRTBO0UCTICW......................................... 1II BETZS* CP TIES LXTBtATORB * .............................2III SXPSRXMESTAL.................................... * . 5XT DXSCUSSIGP CP BBSUXTS AKD COKCLOBICWS................. kOT SCMCABT.........* . . k2

Yl BIBLIOGRAPHT....... kkVII TUft * ♦ • . . ...................................... 51

iii

LIST GST TABLES

I Ionic Vtighte Determined Polarographically » ......... 6

XI Variation of Stop Height vith Change In SupportingElectrolyte Concentration......... . 12

XXX Step Heights vith Cobalt Concentration, IonicCanoentretion and Alcohol Concentration Held Constant . ifc

XV-A Bata Per Job's Method (Hater Solutions)Slit Width at 0.12 sat................................ 22

IV-B Bata for Job's Method (Water Solutions)Slit Width at 0 .0 2 a n . .............. 2k

V-A Bata for Job's Method (Water-Alcohol Solutions)Slit Width at 0 .0 2 on............................... 26

V-B Bata for Job's* Method (Water-Alcohol Solutions)Slit Width at O.Ot on................................ 29

V-C Data for Job1 s Method (Water-Alcohol Solutions)Slit Width at 0.15 as........................... . . * 30

YI-A Data for Speetrophotcmetr ic Titration - Water Solutions 32

VI-B Bata for Spectrophotonetrlc Titration -Water-Alcohol Solutions.............................. 3t

VII Bata for Limiting Logarithmic Method.......... 3d

iv

LIST Iff FIGURES

1 Effect of Alcohol on Step Height......... 102-A Spectral Abeorptancy Curvea .................... 152-B Spectral Abeorptancy Curves...................... 16

3-A Curve Variation - 50$ Alcohol * ................... 183-B,C,D Curve Variation - 0$, 20$, 30$ Alcohol............ 193-S,F Curve Variation - b0$ and 50$ Alcohol * ............ 20M Ccnplezatien Shewn Using Job's Method (Water Solutions)

Slit Width at 0.12 mm............................... 23Canplexation Shewn Using Job's Method (Water Solutions) Slit Width at 0*02 nm. . . ........................ 25

5-A Caaplexation Shewn Using Job's Method(Water-Alcohol Solutions) - Slit Width at 0*02 am. * . 27

5-B,C Caaplexation Shown Using Job's Method (Water-Alcohol Solutions) - Slit Width at 0*0b amand 0.15 m&. ............................31

6-A Spectrophotometric Titration - Water Solution* . . . . 336-B Spectrophotcmetric Titration - Water-Alcohol Solutions 357 Limiting Logarithmic Method . . . . . . . . . . . . . 39

v

ABSTRACT

An explanation for tike tine color formed in the Vogel reaction la proposed. Investigations shoe that pink aqueous solutions containing ecfealt(XX) and thlocyanate ions hare the complexes Co(BCS)* and Co(KS)g- present while the blue color famed when excess alcohol is added to the system is produced when the complex Ge(KCS)g« is present*She mhbcr of water molecules in the coordination sphere of the first complex is undetermined* That the blue color is associated with con­figurations within the eobalt atom itself is Indicated by the fact that addenda other than thlocyanate nay give complexes showing the sane spectral characteristics as the thlocyanate compound. Likewise, various alcohols used to develop the color in this reaction all produce colors having similar characteristics*

vi

INTRODUCTICBf

Cobalt(II) salts reset with thlocyanate lone to fom complexes which are soluble in water and which have colors of approximately the sane hae ae hydrated edbalt(H) ions. Upon addition of organic solvents, such as ethyl alcohol or acetone, a bine color is produced; this color formation is important for the detection and determination of cobalt, and the present study was undertaken to establish the nature of this color and the mode of its formation.

1

BETCES OP TH8 UTSRATURB

Vogel (36) reported the following reaction aa a specific teat for the cobalt(IX) ion. The teat, which now bears hla name, consist a of treating aa unknown solution with solid ammonium thlocyanate after which acetone is added. In the presence of cobalt(XX) a blue color results.

There hare been nany modifications of this test. Mellor (27) gave references dealing with the combination of ammonium thlocyanate solution with amyl alcohol and ether mixtures as solvents. McAlpine and Soule (26) described this reaction as did Bettlnk (3).

Other suitable solvents found wares acetone, recommended by Feigl and Stern (it), Bits (8) and Kolthoff (19) 1 amyl alcohol (7 ), (10), (30) and ethyl alcohol (9), (29), (37).

Cyclic compounds which may serve to Indicate the cobalt(XX) Ion In a thlocyanate salt solution are furfural (33), (3b) and bensyl alcohol (6).

Ions other than thlocyanate have been Investigated. The blue color is produced when thloeulfate ions are used (22) and the sensitivity of the reaction Is said to be Increased If ammonium cyanate Is used Instead of ammonium thlocyanate (12).

The cobalt-thiocyanate complex Is not only useful In the detection of cobalt but also leads itself to the quantitative determina­tion of this metal. One method reported by Rosenheim and Huldshinsky (31) and Heller (28) was the use of standard solutions and comparison with the

unknown* An ether-elcohol mixture was used for the development of color.2

madar (Q) produced ee&ar witli «m^I ileobol and wltk acetone.WwlMMHyit aoaeuranante pmdt tta determination ee little ae O*0Q9$ « M t in

Shi mount d iohalt in a m m y fe# round by uelng tta cOhalt»thioeyiaati mpliK and an anyl AloahiUilhar ntihm (ta)*Uttar Tlswl or jhsModvia aitta d m a x m a D l m m mitohli*

Although a w t a r d theories have tarn postulated to account for tta blue «ota| a© definite m t a t i o i 1* available. H U and t al l (16) pnepoood tta tta color Staagi in ctbalt(II) eelMtiene in too to tta t a r t a t a d a eotat(XI^taB^ao empiOK ion* In < t a A r acidic M d i m (cone ant rated Mineral iota) tta odor of tta solution la tarn oaifioralm to tta reeetient

* n * ( % « r ^ * a^pBed Blue

tan dehydration theory tee net accepted by Baeeett end Crouctar (I). they cXained ttat tta m o o d m d tta t a n , Shiah vae taeed on tta ocoartion of nagneeiun and edtalt osta* woo unjustified and lienee ectalt need not be coordinated to elm eater ndeeulee*

Sta addition of a eeneeatrated eolation of maaenlum thlocyanate to a eolation of a oebalt(XZ) ealt could be represented bys

CoClg f 2TO W36 ^ mfySX * Co(RC8}gend

co(bcs)2 4 m^nes -----^ (BH^gCotncB)^according to Mailer (£?)•

Reeal (3d) bubbled dry hydrogen oblerido thmgi a 0*1 M attaene CoClg»6Bg0 Catalan* the eolutlon changed free a pink to a blue

h

color. He believed that the cdor is caused by a compound formation «f tha types

aCoCl3*oBgOtime poaalbla explanation aa to the formation of tha color by

dehydration say ba aham by tha equation (ll)s

a^otHjjOj^Jcig < co(coci*) * 1 2 ^ 0

Pink BlueTeigl (13) explained that tha blua color la probably due to

BolTat* fanatic* irith ocaplax cofcalt-thiocyimatee eueh aa *gjco<W»)fc]. Upon dilution tha color returns to pink* Shis appears aa tha raault of tha fosnatlom of tha Co(HCS)^ * Iona (12),

Young and Ball (feo) pointed out that tha capacity of a advent for preventing decomposition of a complex varlaa invaracly aa lta dielectric cenatant and that tha ecmplax fornad vith cobalt and ammonium thiocyanata la extracted from aqueous solutions by organic advent a.

Abserptaaey corves have boon run on solutions of cobalt thiocyanata in non aqueous advents* In a non aqueous solvent, L# tha complex Co(KS)gLg la formed (18). The ccoplex Co(HCS)* is present in aqueous solution* containing an excess of cobalt vhlle an excess of thlocyanate produces Co(ICS)^ (17)*

KXPJKEUMEffllPAL

By mesne of the Jander equation (21) ionic weights of same complexes can be determined polarographlcally • The diffusion current coefficient of the ion under investigation Is found by obtaining a polarograa of that ion and then using the liberie equation (20)*

14 : 605 C .

id - diffusion current In micro asqteres,n = number of faradays of electricity required per

molar unit of the electrode reactant.D s diffusion current coefficient of the reducible or

oxidisable substance.C = concentration in millimoles per liter, m = rate of floe of mercury in ailligraas per second, t • drop time in seconds.

The Jander equation, which follows, is applied and the ionic weight determined.

*x ---**

Mx - ionic weight of the unknown ion.- ionic weight of the known ion.

Zjg - viscosity of the known solution.Bjg - diffusion current coefficient of the known ion.Dx - diffusion current coefficient of the unknown ion.

5

The viscosity (Z) of the solution la calculated from

Z X “ 4 ^ 0 ^ 0

Z viscosity of water in poise*- viscosity of unknown in poise*" density of solution in grams per milliliter*Z time for the unknown to drain through Ostwald viscometer*- density of water*- time for an equal amount of water to drain through

Ostwald viscometer.A shift of the half-wave potential in a polarogram indicates

complex&tlon and the coordination number can he calculated from it (23)* Thus, polarography seemed a logical approach to the present problem.

A suitable organic solvent as a developer of the blue color was chosen using the following criteria: one, it must not be oxidizable

tor reducible at the half-wave potential for the complex; two, it must not be so viscous that it interferes with polarographic measurements; three, It must have a different weight from the HCS~ ion* The purpose of the first criterion is obvious, while the second restriction is necessitated by the viscosity factor in the Jander equation* Xf the solvent were coordinating, a weight difference is needed to show it, hence the third restriction.

Of the organic solvents tested acetone gave the deepest color* Polarograms of the cobalt, thlocyanate, water and acetone system exhibited irregularly shaped curves indicating a half-wave potential for the reduction of the acetone near that of the cobalt complex* Thus acetone was unsuitable since it did not meet requirement number one*

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existed between the height of the wave and the concentration of the ion reduced (bl) . Abnormally large step heights have been reported in the nee of system* containing a high percentage of sugar, The diffusion currents became systematically higher as the viscosity increased. An explanation for the anomalous diffusion currents in sugar solutions may lie la some action of the dielectric properties on the interionic attraction (35)•

From these data It appeared that no definite Ionic weight could be assigned to the complex giving the blue color because of the various uncontrollable factors pertaining to the polarographic method.To determine qualitatively if conplexation occurred a series of studies were made on cobalt-thlocyanate solutions having varying amounts of organic solvent and ranging in color from pink to blue (Figure 1) •Both ethyl and methyl alcohol were used. Since the step height of the polarogram Is an indication of the ionic weight a curve of step height versus percentage by volume of organic solvent was plotted. Due to the changes in density and other factors the step height declined. Bo break in the curve occurred hence giving no indication of a new type ion formed at a definite water-alcohol mixture.

The scat, potassium selenocyanate, was prepared following the method outlined in "Inorganic Syntheses Vol. II" (15). It was found that a blue color is produced by mixture© of this salt, cobalt(II) ions and ethyl alcohol. The procedure used with IQXCSe was the same as that used in the KHCB studies and similar results were obtained.

Best a series of tests were made with a solvent having a fixed ratio of alcohol to water, and the amount of potassium thlocyanate varied. In this way the dielectric constant remained fixed. Polarograms

STEP

HE

IGHT

^C

MS.j

10

FIGURE I

EFFECT OF ALCO HO L

ON STEP HEIGHT

E T H Y L A L C O H O L

M E T H Y L A L C O H O L

PERCENTAGE OF AL C O H O L BY VOL' JME

S O L J T I O N . 0 . 0 0 9 7 9 M IN L o ( n j

0 . 0 zi 7. IN G E L A T I N

0 . 5 M IN K N C S AT 2 5 ° C .

u

obtained in these eases shewed that the step height remained constant after a ratio of Co(XX) to HC8~ of 1 to was obtained. Between the ratio of X to k and X to X the step height gradually Increased. However, uaing potassium chloride, which did not give the blue color, the ©am© phenomena occurred (fable XX). This has been observed before (33) and is attributed to the movement of the indifferent electrolyte at the surface of the cathode which depends upon the concentration of this electrolyte. Sodium thiosulfate which gave the blue color was also used la these studies. At the same ratios and concentrations the step heights with all three salts were practically the same.

When potassium chloride was used as a supporting electrolyte a break in the wave was noted. According to Xtlngane (2h) It is caused by the reduction of the hydrosypentaquo cobalt (II) ion and disappears upon acidification. Vo such wave occurred when HGS~ or Ionswere used as supporting electrolytes. Because of this, these are re co m m e n d ed for use in polarographic determinations of cobalt.

The half-wave potential of the cobalt wave in thiosulfate solution was rare positive than that obtained in thlocyanate solutions. The wave obtained In thlocyanate solutions In turn was more negative than that Obtained in chloride solutions.

Since a change in density causes a change In step height as does change In Ionic concentration both were held constant over a range of values for thlocyanate Ion concentration. By having the same amount of alcohol in each sample the same macro dielectric constant was held throughout this phase of investigation. As the amount of potassium thlocyanate was reduced in the system the ionic concentration was held constant using an Indifferent electrolyte, sodium acetate. The polaro- graph recorded no noticeable change in ionic weight (step height), while

12

TABUS IXVariation of Stop Height n t h Change in Supporting Electrolyte Concentration

Solution Hatio of Supporting Step BolghtElectrolyte to Cobalt an*

1 5041 30*0

2 4031 30 .0

3 30:1 30.0k 20sl 30 .0

5 1041 30*06 841 30*0

T 64I 30.0

8 bil 32 .0

9 241 35.010 141 38*0

11 5041 31*.0

12 141 fcl.O13 5041 3U .0

lb 1 :1 %1 .0

13 5041 3^.016 141 to.oSolutions 1-10 XBCS, 0.02$ in gelatin, 30# in ethyl alcohol

0*098 if in cobalt*11 -12 Sane aa 1 to 10 only KC113-lb Same aa 1 to 1015-16 Sane aa 1 to 10 only HagSgO^

13the color of the system changed ft cm blue to pink (table III), the

pat*atl,a 414 •“ ** ^ ■**» * • exp8Ct9d changing from a supporting electrolyte of potassium thlocyanate to sodium acetate.

From the foregoing it le eeen that the polarograph did notreveal any change in Ionic weight going from the blue to pink color;also the restrictions of the eyetea prevent using change of the half* wave potential to detaxmlne any change in coordination number if such occurred.

Spectrophotometry was next employed ae a means of studying the nature of the blue color. Brode (b) has determined the structure of complexes by apeetrochemieal means. In this method a aeries of curve* are obtained for the system under consideration. Bach curve is different from the rest when there la a variation in the amount of one of the members of the system. The amount of ccssplexatlon la in­dicated by changes In the curve.

In these investigations a Beckman Model W Spectrophotometer was used. At the outset data were gathered for various ay stems and the curves drawn (Figure 2). The optical density, D, versus wave length in millimicrons, mu, was plotted. A simple system of cobalt(H) ions la water was obtained first and then the system changed by adding different electrolytes. A change in intensity in the red region,510 n , was observed. Systems which contained different alcohols were investigated next. This change in the system caused an absorptance peak to occur in the blue region of the spectrum; the peak of absorptence in each of these eases was at 620 mu. Feigl (13) noted that the absorptanc® curve is the same regardless of solvent used* These studies showed farther that the peak in the blue region was at the same point, 620 mu,

TABLE XIXStep Heights vlth Cobalt Concentration, Ionic

Concentration and Alcohol Concentration Held ConstantSolution HaAc KNCS Step Height ®t/q

(nolarity) (aolarity) na« '

1 0 .2 0 0 92 -0 *9*$2 0.05 0.15 91 -1*09

3 .025 0.175 90 -1.17h .010 0 .1 9 39 -1.235 o 0 .2 0 87 -1*5^

S , against S.C.2.1/230# ethyl alcohol - O.OSji gelatin

OP

TIC

AL

DE

NS

ITY

w

FIGURE 2

SPECTRAL ABSORPTANCY CURVES

A.

o

0 . 5

06 7 04 9 03 10

WAVE L E N G T H I N M p

1 C o ( U ) » H 2 °

2. , H2 O , NCS~3. Co^jX/ > H 2 C » N C S “ ,

M E T H Y L ALCOHOL4. Co(Cj ( H2 0 > N CS ,

E T H Y L AL COHOL5 Co(n) , H^O , N C S -

T - R U T Y L AL CO HO L

FIGURE 2

SPECTRAL ABSORPTANCY CURVES

B.

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<u1 . 5 -Q.O

4 9 0 6 70WAVE L E N G T H I N M p

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2 . C o ( i i ) , H 2 O j N C S e fM E T H Y L A L C O H O L

3. CotI, , H2 0 , N C S e -ET H Y L A L C O H O L

3' ^ » H2 O > NCSg tT - B U T Y L A L C O H O L

(s o l u t i o n s u n s t a b l e )

XT

in systems which had different lone to develop the blue color* Water solutions of the potassium selenocyanate salt vere found to he stable for only a short period of time. Without further work it would prove undesirable as a reagent for the cobalt test*

A method of curve variation similar to that of Brode (5) and Kiss and Caban (17) was used on vater-alcohol systems with results shown in the series of curves, figure 3* With the ratio of water to alcohol held constant the ratio of cobalt to thiocysnate was varied (figure 3 A)* The optical density curves shown in figure 3 B, C, D, £ and f are of solutions containing ratios of cobalt to thiocysnate of 1 to 5* 1 to 6 and 1 to 7* Solvent composition was varied from 0$ ethyl alcohol to 50$ ethyl alcohol. These data showed a deepening of color at a wave length of 620 mu when either the thiocysnate to cobalt or alcohol to water ratio was increased. However, the structure of the ion responsible for the deepening of the color could not be deduced by this method.

According to Yosburgh and Cooper (38) the ratio of catnplexa- tlom can be determined by means of a spectrophotometer using Job*s method of continuous variation. Zquiaolecular solutions of the Ions ware used and they varied the proportions of each from 100$ to zero while the total molarity was kept constant. A plot was made o f the difference In optical density at a given wave length versus the mole fraction of ccxsplering ion. This difference was obtained by subtracting the optical density given by straight dilution of the system from that obtained from the addition of the non-colored complexer*

Yosburgh and Cooper developed the following expression to determine the amount of ecmplexation*

OP

TIC

AL

D

EN

SIT

Y

FIGURE 3 CURVE VARIATION

A. 50 % ALCOHOL

RATION C S '20

0 . 5 -

5 0 0

WAVE L E NGT H UN M

4 0 0 600 7 0 0

OP

TIC

AL

DE

NS

ITY

19

FIGURE 3 CURVE VARIATION

B. 0 % A L C O H O L

4 0 0 500 6 0 0

C. 2 0 % A L C O H O L

0 3 -

0.2-

4 0 0 5 0 0 6 0 0

D. 3 0 A L C O H O L

0 . 3 -

0.2 -

TT * 1-4 0 0 5 0 0 5 0 0

WAVE LEN GT H IN Myu

R A T I O Co(n) N C S

1. I 52. I 63. I 7

0.17 7 M Coju)

OP

TIC

AL

D

EN

SIT

Y

20

FIGURE 3CURVE VARIATION

E . 40*7* A L C O H O L

0 . 3 -

0.2-

0 .1-

4 0 0 5 0 0 6 0 0

F. 50<7. A L C O H O L

0.7“

0 .6-

. 5 -

0.4-

0 .3 -

5 0 04 0 0 6 0 0WAVE L E N G T H IN

RAT IO C°(n> N C S “

1. I 52. J 63 I 7

0.177 M Coqij

where9 z coordination numberx - amount of eomplexing Ion present at maximum difference

in optical density.Job’s method mas applied to the cdbalt-thiocyanat© system and theabove formula used. For aqueous solutions H was found to equal one,indicating that a mixture of Co(ll) and ACS ions may contain semeCo(ECS)* ions in solution. This iras found to hold for several savelengths (Figure b A),

The effect of adding alcohol to the system was studied.Data were Obtained using two Beckman Spectrophotometers. In oneinstance the slit width was in the range of 0.15 and in the other,the slit width in the range of O.Ot am was used. As before, watersolutions of cobalt-thiocyanat e were examined both In the red andin the blue regions (Figure k A and B) • Cobalt-thiocyanat© solutionswere prepared by adding the necessary amounts of cobalt nitrate and

(

potaesime thiocyanat© solutions, 10 milliliters of absolute ethyl alcohol and enough distilled water to make a total volume of 25 milliliters. Again Job's method was used and data obtained in both spectral regions. Figure 5 A shows the results in the red region. The addition of the alcohol did increase the optical density and the optical density difference, but the shape of the curve remained the same. The difference in optical density between 0.8 and 0.9 mole fraction NCS~ was the same value in both water and vater-alcohol systems. In the blue region the optical density due to the cofoalt(ll) ion and Co(HCS)~ ion was very low in water solutions end an Increase due to the addition of alcohol would be small. Hence in vater-alcohol systems of cobalt-thiocyanat ©

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R 3 f tmm & f t f t ©

d d d © © dii

© © © t

f t s ft 3cn

jitm

f t f t VOPi f t

d o o d#

© d © d#

© ©

&cniH a s i a &

mOS 3 f t ft#

H4

H*

p-i*

H*

HI*

iH d d-*

Q d

$ & a d **4ft sr tft 3ft 3 3 P £♦

o H H H r4 H d d O ©

<3 3 Si ft $ S p ftd O d o © d d d © ©s 3 3 3 3 ft s ft f t Rd O

•© © d d•

© o © d

r lf CU• m•. a>

* (A• VO• r**• 40■* f t f t

o O © © © © © 0 © o

rH O! <n d t ITS vo I** CO os o*4

23

FIGURE 4

COMPLEXATION SHOWN USING j o b ' s METHOD

(WATER SOLUTIONS)

A. S L IT W ID T H AT 0 .12 M M .

>- 0 9 -1-</)zUJ 0 . 8 -Q

0 . 7 -<OF 0 . 6 -£LO

0 . 5 -z

u 0 . 4 -OzLU 0 . 3 -trLl)u.u. 0 . 2 -Cl

0 .1 -

0 -

MOL E0 . 5

F R A C T I O N NCS

Co,in i NCS»2. SAME3. SAME4. SAME5. SAME

CO. 2 00

AT 5 2 0 M

AT 5 0 O AT 4 8 0 MfA AT 4 60 M|n AT 5 b 0 Mja.

M S O L U T IO N S )

TABLE I?Bata fear Job's Method(Water Solutions)

B. Slit Width at 0.02 on.Solution Wole

fractionscs-

D (Optical Density) at Wave Lengths in on

500 510 620D'Co(n) Diluted at Wave Lengths in an500 510 620

0 - 0* at Wave Lengths in an

500 510 6201 0.10 0*93 0.98 0.059 0.7* 0.78 0*093 0*19 0*20 0.0062 0.20 1.01 1.07 0.057 0,66 0,70 0*0*7 0*35 0*37 0.0103 0.30 1.08 1,1* 0.057 0*37 , 0,61 0.0*2 0*51 0*53 0.0.5* 0**0 1.10 1.16 0.056 0**9 0.52 0*036 0.61 Q.&k 0.0205 0.*5 1.07 1.13 0.052 0**5 Q.kf 0*033 0.62 0.66 0.0196 0.50 1.07 1.13 0.051 0.*1 o M 0.030 0.66 0.7® 0*021T 0.55 1.02 1.07 0.0*9 0*37 0.39 0.027 0*65 0.68 0.022a 0*60 0.97 1.02 0.0*5 0*33 0.35 0*02* 0*6* 0.67 0.0219 0*70 0.6l 0.86 0.037 O.25 0.26 0.01S 0.56 O.60 0.01910 0.60 0.63 0.6? 0.028 0.16 0.18 0*0X2 0.*7 0.1)9 0.016u 0*33 0*33 0.015 0.08 0.08 0.007 0.25 0.2? 0.00812 0.00 0.02 0.67 0.05a «» » mr

DIF

FE

RE

NC

E

IN O

PT

ICA

L

DE

NS

ITY

25

FIGURE 4

COM PL EX AT ION SHOWN USING j o b ' s METHOD

(WATER SO LU TIO N S)

B. S L I T W I D T H A T 0.02 M M .

0.6-

0.5-

0.4-

0.3-

— o— — o —

0.5 1.00MOLE F R A C T I O N N C S “

1. C o^n;, N C S " A T 510 M ^

2. S A M E A T 5 0 0 Mjuc

3. S A M E A T 6 2 0 M pCO.4 4 3 M S O L U T I O N S )

26

TABLE VBata Tor Jefo’e Method (Wat ar-Alcohol Solutions)

A, Slit Width at 0*02 Bn.Solu- Kola B D*Co(XI) Diluted D * 1)1tlon Fraction (Optical Density)

■®* 500 ml 510 m p M 510 wu. 500 m 5%Q m

1 0*10 0*98 1*03 0*77 0*82 0 .21 0*21

2 0*20 1.07 1.13 0*60 0*73 0 .3 9 0 **0

3 0*30 1 .1* 1*22 0*60 O .63 0.5^ 0*37* 0 **0 1*18 1*25 0*51 0*55 0 .6 7 0*70

5 0*50 1.15 1 .2* 0 **2 0 .*6 0.73 0*786 0*60 1 .0 7 1*13 0*35 0.37 0 .7 2 O .76

7 0*70 0 .89 0*95 0 .25 0*27 0 .6k 0*68

a 0 .8 0 0*66 0*71 0*16 0 .1 8 0 .5 0 0*339 0*® 0*53 0*57 0*12 0.13 o.fcx 0 .**

10 0*90 0.36 0*39 0 .0 8 0.09 0 .2 8 0 .3 0

11 0 .0 0 0*86 0*91 - m m 4*

27r ■ ■ ■

FIGURE 5

COMPLEXATION SHOWN USING JOB'S METHOD

(WATER-ALCOHOL SOLUTIONS)

A. S L IT W IDTH AT 0 .0 2 MM.

o.s>-S 0 .7- zkJQ 0.6

z- 0 .3iiioz 0.2 UJcnIdk. 0.1O

0 . 5MOLE F R A C T I O N N C S "

A.1. C o ^ ) , N C S ” AT 510 Mjx

AND 5 2 02. SAME A T 5 0 0

( 0 . 4 4 3 M SOLUTIONS)

the optical density In the blue region was so predominately due to the new species of cobalt thiocysnate ion fomed that the optical density caused by cobalt and Co(HCS)^ lone could be disregarded* The shape of the curve obtained by Job's method remained essentially the same and valid deductions could be made from it* At both slit widths (Figure 5 B and C) and several wave lengths the maximum optical density occurred in the region O.85 to 0*86 mole fraction BCS~. This corresponded to a complex of the composition Co(lfCS) | .

Although every position in the coordination sphere is occupied* a series of solutions were investigated to determine if the alcohol coordinated. Both 1 to 1 and 1 to 6 cobalt-thiocyanate ratios were used. Bthyl alcohol at more than forty times the molar concentration

I ___ *of the Co(HCS) and of Co(HCS)gr was required before the first sign of the characteristic blue hue was discerned thus indicating that there was no alcohol coordinating in the complex.

The formation of the Co(BCS)^: Ion was also shown by means of a spectrophotometric titration (39) • A number of solutions were prepared all containing the same concentration of cobalt. Different amounts of BCS~ were added ranging from 0 to 15 times the amount of cobalt present. Figure 6 A gives the results in water solution and Figure 6 B those in yyft ethyl alcohol solution. Coordination combinations are Indicated by a break in the slope of the curve* Optical Density versus the ratio of BCS* to Qo( II). The optical densities of the water solutions were measured at 510 mu. A break In slope was observed at a ratio of Co(IX) to BOB* of 1 to 1. At a ratio of 1 to 6 a slight break was also observed. The concentration of cobalt ion* 0.00885 M* was much too low for optical density measurements at 620 mu. Alcoholic solutions had a pronounced break at cobalt to thiocysnate ratios of 1 to 6 measured at a

29

TABLE VBata Tor Job*e Method

(Wat ar-Alcohol Solutions)B. Slit Width at O.Ot on*Solution Mole

Fraction

1acs"

0.102 0.20

3 0*30

k o.fco

9 0.50

6 0.60

7 0.70

8 0.80

9 0.82

10 0.6k

11 0.85

12 0.86

13 0.68Xk 0.90

19 0.99

16 0.00

D(Optical Penalty)600 Utt 620 mu0.071* 0*0620.077 0.0620.087 0.070O.IO8 0.0900.H*2 0.1280.207 0.2050.308 0.3300.1*09 0.1*580.1*30 0A 880.1*32 0.1*930.1*1*5 0.5010.1*37 0.5010.1*22 0.1*850.385 0.1*1*1*0.258 0.3020.068 0.059

30

TABLE VPats for Job's Method

(Water-Aleohel Solutions)C. SUt Width at 0.15 as.Solution Mole P

Fraction (Optical Penalty)PCS* 590 mu 600 8SU 620 mu

1 0.50 0.162 0.150 0.1522 0.60 0.21b 0.219 0.238

3 0.70 0.280 0.313 0.356b 0.80 0.330 O .385 0.b52

5 0.82 0.337 0.397 0*b6S6 0 .8b 0.3*3 O.b09 0 .b8l

T 0.86 0 .3b0 o.bos 0.b7b8 0.88 0.316 0.38b 0.b559 0.90 0.293 0.356 0.b25

10 0.92 0.263 0.317 0.382

11 0 .9b 0.219 0.266 0*32212 0.96 0.173 0.208 0.250

13 0.96 0.06b 0.117 O.lbb

31

zuio—I<ut-Q_O

FIGURE. 5

COM PLEXATlON SHOWN USING JOB'S METHOD

(WATER-ALCOHOL SOLUTIONS)

B. S U T W I D T H A T 0 . 0 4 M M .

0 . 5~

0 . 4 -

0 . 3 -

0.21o. H o t r

0 . 5MOLE F R A C T I O N N C S “

1. , N C S ” A T 62 02. S A M E A T 6 0 0 M j a

C. S L I T W I D T H A T 0.I5 M M .

> O

HV) 0 . 4 -ZtxJQ 0 . 3 -

0 . 2 -O£Q. 0 . 1 -

0 . 5F R A C T I O N N C S "M O L E

1. Co(jj) , N C S " A T 6 2 02. S A M E A T 6 0 0 M ja3. S A M E A T 5 9 0 M u

(0.443 M S O L U T I O N )

32

ZASLK VI Dmta for Spectrophotcmetric

A* Water SolutionsStatic of

autlon . m .ffotlf)

1 0*0002 0.5153 2.58* 3.8T5 5.156 7.?2 '7 W.38 12.99 15*5

fitretlon

D(Optical Density)

510 mu0.0*30.05*0.0900.1030.1160.1320.1**0.1510.163

OP

TIC

AL

D

EN

SIT

Y

FIGURE 6

SPEC TROPHOTOMET RIG

A. WATER SOLUTION 0 . 0 0 8 8 5 M C o ^ )

0.2-

O.l -

510 M

5

RAT 10 OF

r rN C S 'Co(n)

TITRATION

Ul

34

TABUS T I

Bata for Spactrophotaaotrle Titration• Vat«r-Alcohol Solutions

olutionRatio of UCS-w

D(Optical Density) 510 wu 620 am

1 0.000 0.0452 0 .515 0.065

3 2.58 0.113 0.0141* 3.»r 0.127 0.0205 4.12 0.134 0.0246 5-15 0.145 0.0377 7.72 O.I65 0.0898 10.3 0.179 O.I83

9 12.9 0.1Q5 0,33910 15-5 0.196 0.495

OP

TIC

AL

D

EN

SIT

Y

FIGURE 6

SPECTROPHOTOMETRIC TITRATION

B. W A T E R -A LC O H O L SOLUTIONS 0 .0 0 8 8 5 M C o ^ )

0.5-

0.4-

0.3-

0.2-

620 M

105 150RATIO or N C S '

c<>(n)

36

wave length of 620 mu. The optical density was too low for readings in the 1 to 1 ratio range. At the wave length of ?10 mu the 1 to 1 and 1 to 6 ratios of Co( II) to KCS~ were shown as In the water solution*

In an attempt to eonflra further the results already obtained In this study, the limiting logarithmic method (2) was applied*Consider the following chemical reaction:

(1) nA | aB Vi,where n moles of A react with m moles of B to fora the product A B .e a ttThe equilibrium constant for this reaction may be expressed by

(2) K -or

w m ‘

(3) = [«A]and tairing the log of both sides the following expression was derived:

(t) n log * m log jVJ 4* log K - log If exhibits a color, the amount of formed is related to theoptical density of the solution* In this method, if the concentration of A is held constant the change in optical density is observed when the concentration of B is varied* With [A^ held constant the equation may be written

(5) leg D - m log pi] I k with k - log TOL [a] n where B Is the extinction coefficient and D is the optical density. Equation (5) is of the straight line fora with slope m when log B is plotted versus log [b] . In the equation developed the slope m gives the amount of B ccmplexing when log £ la plotted against log . Also, by holding the concentration of B constant and varying

37

the concentration of A, the number of A particles, n, coordinated with B can he determined.

fable VII summarizes the data obtained at 620 mu shovn graphically in Figure 7 * The slope of the Co(II) curve was 0 A 28

and that of the HCS* curve was 2.57 giving a slope ratio of 1 to 6.This investigator attaches no significance to the ratio of

slopes because the absolute values of the slopes should have been 1 and 6 . The limiting logarithmic method assumes that the amount of formed is negligible compared to the amounts of A and B; and further, that the concentrations of A and B at equilibrium are essentially the same as before the reaction occurred. Since Job*s method of continuous variation shoved Co(HCS)^ to be present in blue colored solutions the concentrations of A and B at equilibrium are not the same as the initial concentrations even if only a slight amount of AjBm were formed. These observations combined with the fact that an appreciable amount of AnBm could have been formed (there is no proof pro or con) suggest that the slope ratio of 1 to 6 Is merely circumstance.

At extreme dilutions of cobalt(II) and concentrated solutions of thloeyanate no straight line could be obtained using this method.

38

TABLE VXIBata for Limiting Logarithmic Method

lain-ilm

• Cenc*n- tration Co(II)

Concan- trationk b '

Log C s(Optical BtHltr)610 an 620 hu

Log D 610 mu 620 HU

1 0.008891 0.0507M -1.295 0.045 0.047 -1.346 -1.328z O.OO885M 0.0760* -1.119 0.123 0.130 -0.910 -0.8863 0.008891 0.101H -0.99^ 0.262 0.274 -0.572 -0.562% O.OO883H 0.152* -0.818 0.684 O.695 •0.165 -0.1585 O.OOSSQM o.xom -2.053 0.262 0.274 -0.572 -0.5626 0.0133* 0.X01M -I.876 0.323 0.337 -0.491 -0.4727 0.0177M O.101M -1.752 0.373 O.389 -0.428 -0.4108 0.0266* 0.10IM -1.575 0.440 0.457 -0.356 -0.340

5<# Bthyl Alcohol Solntimu

39

FIGURE 7

L IM IT IN G LO G A R IT H M IC METHOD

- 0 . 5I-1I<0u

oo-I

- i . o S L O P E

0. 5O P T I C A L D E N S I T Y

1.5 1.0L O G

0

- 1.0 -

-1 .5

S L O P EOO_»

-2.0 -6 2 0 M

2 . 51.0

LO G1.5 - 0 . 5

O P T I C A L D E N S I T Y0

2 . 5 7

0 . 4 2 8

J

DISCUSSION m BESUItfS AND CONCLUSIONS

A change of color in a system may indicate a change in Ionic structure. Cobalt( II) -aleohoX-vater systems are involved In such a change when either thiocyanate or thloeulfate ions are added* Since their Ionic weights are quite different if either of these ions were added to the edbalt ion ae addenda, the ionic weights of the resulting complex would be different. Chloride lone in the concentrations used do not produce any color change.

Polarographic studies have been made on various cobalt* thiecy&nate systems and the following statements can be made 2 in vater-alcohol solutions containing cobalt(XI) ions and chloride or thiosulfate or thiocysnate Ions, the Ions diffusing into the mercury drop and being reduced were of the same weight. Such a result indicated that the cobalt complect formed in causing a change from a pink to blue color was unstable under the conditions of these experiments and was disrupted in each case into a cobalt ion, perhaps of the structure Co(llgO)^ , before reduction occurred. This was reflected by the diffusion current, id> since it was the same for similar concentrations of cobalt(II) ions, of the supporting electrolyte and of the alcohol.

Spectrophotcmetric studies showed the formation of a pink complex in water solutions with a ratio of cobalt to thiocysnate of 1 to 1. Job's method and the method of spectrophotometrlc titration both gave this result. By the latter method the complex Co(NCS)^*In water solution was also indicated. Both methods proved the blue color resulted from the formation of Co(NCS)^I ions produced in

fco

*j U nI j i i f • i i i

i Q\

a

I f I * 8 I

! I ' h • n

iiiiiin! i ! •« h *

i

§ f

i f i h

* f is! i!« f I _

f t ; * *

s

I

o

ai !ii%

If

%

H

SUMMARY

1* The Vogel reaction has been Investigated both polarographicallyand spectrophotoaetrieally •£• Vo change in ionic weight in the transition from the pink tobine colored eolation was indicated by polarographlc studies when using either the absolute or comparative methods of ionic weight determination.V

In the course of the polarographlc investigations the selenocyanate Ion was found to give the Vogel blue and these organic solvents} formic acid, n-butyl alcohol, isopropyl alcohol, n-propyl alcohol, diethylene glycol, tert-amyl alcohol, methyl alcohol and tert- birtyl alcohol hitherto unreported, were found to develop the blue color*k. The structure of the ion responsible for the deepening ofcolor at a wave length of 620 mu in alcoholic solutions could not be deduced by the curve variation method* A deepening of color was produced when either the ratio of thiocyanate to cobalt(IX) or alcohol to water was increased.5 . The method of continuous variation showed the complexCo(SCS)^ present in pink aqueous solutions of cobalt and thiocyanate ions when measurements were made at wave lengths of 510 and 620 millimicrons. In blue alcoholic solutions at the wave length of 620 millimicrons the complex Co(HCS)^ was shown to be present.6 . The method of spectrophotometrlc titration at a wave length of510 millimicrons showed the presence of Co(MCS)* and Co(NCS)^r in water

k2

h3

solutions and In alcoholic solutions; at 620 millimicrons the titration shoved the formation of the complex Co(J3CS)gS in alcoholic solutions of cobalt(IX) and thiocyanate ions*T • When the limiting logarithmic method was applied to alcoholicsolutions at a wave length of 620 mu the data did not give results of immediate significance because of uncertainties concerning the condition of the system at equilibrium.8. Since various addenda and alcohols gave complexes having thesame spectral characteristics the blue color was proposed to be associated with configurations within the cobalt atom itself.

BIBLIOGRAPHY

Bassett, H. and Croucher, Hi B.A phase-rule study of the cobalt chloride colour change,J. Chen, Soc. 1930s 17^-1819 (1930)

Best, M. B. and Trench, C. L.She structure of ferric thiocyanate and its disaasociation In aqueous eolation,J. As. Chen, Soc, 631 568 (19^1)

Bettink, H. W.Beektioa auf kobalt bei gegensart eisenverbindungen.Bed. ^dschi. Phare. 11: 61i~5 (1899)Chen. Zentr. 1899 - IJ 90k (1899)

Brode, V. B.She absorption spectra of cobaltous compounds.Ill, The pyridine and quinoline complexes and solutions. J. An. Ch«m. Soc. 53* 2*57-67 (1931)

Cart ledge, G. B. and Bricks, W, P.Equilibrium between the trioxalatomanganiate and dlazalatlodlaqucmanganlete ions.J. Am. Chem. Soc. 58: 2065-9 (1936)

Chariot, 0. and Benzler, P.Hew procedure for the detection of cations.Ann. chim. anal. 25: 90-h (19*3)C.A. 38t 5*707 (19V0

7. Danzizer, J. I*.A new qualitative test for cobalt.J. Am. Chen. Soc. 24s 578-80 (1902)

8. Sits, H.Detection of Hn end Co.Chen. Ztz. 46: 121 (3.922)C.A* 16: 1372 (1922)

9. Deyer, F. P.The macrcdectlon of cobolt. Sane modifications and new colorimetric tests.Australian Chcm. Inst. J. and Proc. 3: 239-44 (1936)C. A. 31* 653 (1937)

10. Beyer, 7. P.Maerodetectlen of cobalt - acme modifications and nee tests. II.Australian Cham. Inst. J. and Proc. 3: 277*80 (1936)C. A. 3ls 9701 (1937)

11. S m X a u and Anderson"Modern Aspects of Inorganic Chemistry".D. Van Nostrand Company, Inc., Bee York, 7, Y.(1938), p. 1 M

12. Engelder, Dunkelberger, ShiUer"Semi-Micro Qualitative Analysis".John Wiley and Sons, Inc., New York, 7. Y.(1936), p. 159

1 3. Felgl, 7."Qualitative Analysis by Spot Tests".Elsevier Publishing Co., Inc., New York, 7, Y.(1946), p. 112

46Feigl, 7. and Stern, I*

Ober die werwendung von tupfelreaktronen in der qualitatlven analyse.Z. anal. Chan. 60s 1-^3 (1921)

15. Frenelua, W. C.’ Inorganic Syntheses”.McCrair-Hlll Co., Inc., Nev York, N. Y.(19^6) Tdl. II, p. 186-8

16. Sill, B. and Sowell, 0. B,Crystal Structure and absorption spectra. The cobaltous ccepounds.Phil. Hag. kSt 833 (192V)

IT. Kiss, A. and Cskan, P.Zur lichtabeorption der hobaltrhodanidlosungen.Z. pfcyslk. Chen. Al86: 239-*7 (19^))

18. Kiss, A. and. Cskan, P.Zur lichtabsorption eon kobaltrhodanidlosungen,2. Vasser - nichtelektrolyten als losungsnlttel.Z. physick. Chen. Al88: 27-H0 (19*1)

19* Kdthoff, I. K.The cotoalt-thiocyenate reaction for the detection of cobalt and thiocyanate. ltlkroehemle 8$ 176 (1930)

20. Kolthoff, I. H. and llngane, J. J."PoXaregraphy".Interscience Publishers, Inc., See York, B. Y.(19*1), P* 80-2

kj

21. Kolthoff, X. II. and Watters, J. X*Polarographlc dot erraination of manganese ae tr i-dihydrogen pyraphoepha t oanangani ate.Ind. Fng. Cham. An. Bd. l t 8-13 (19^3)

22. Karenman, X. M. and Askbel, E. M.Fractional reaction for cobalt.Bavodakaya Lab. IDs ^93 (19^1)C. A. 33s 787I6 <19*1)

23# Lingane, Janas J.Interpretation of the polarographlc vavea of complex natal lens.Chen. Bar. 29: 6 (19*1)

2h. Lingane, Janas J.Interpretation of the polarographlc wave© of complex natal ions.Chan. Bar. 29: 3* (19*1)

25. Mader, B.Colorimetric determination of Co as the cobalt thiocyanate complexDie Chenle 55* 206-7 (19*2)C. A. 37: **98*

26. McAlpine and Soule"Prescott10 and Johnson's Qualitative Chemical Analysis".D. Tan Hostrand Co., Inc., Her Tork, W. I.(1933), P- 332

k&

27* Hellor, V,“A Comprehensive Treatise on Inorganic and Theoretical Chemistry".LongRan's, Green and Co., Heir York, H. Y.(1915) Vol. XIV, p. 516

26. Kellor, JT. W.Colorimetric determination of cobalt in presence of nickel. Trans. Sag, Cer. Soc. 8 : 135 (1908)C. A. k: lkkO (1910)

29* Morrell, T. T.Chemtsche analyse organ! scher korper.Z. anal. Chem. 16: 251 (1877)

30. Pregl, V."Quantitative Organic Microanalysis”.P. Blakiston*s Son and Co., Philadelphia

•t

(1937), pi 13*31. Bosenhela, Arthur and Huldshinsky, Ernst

Sine methods zur quantitativen trenming von nickel and kobalt. Ber. 3*n 2050-7 (1901)

32. Bosai, LuisA nee reaction for the cobalt ion.Berv* aeoc. bioquim. argentenia 9 Ho* 33s 11-13 (19 3)C. A. 3&i . 623b (1937)

33 . Ryazanov, I* Pi

Detection of cobalt with furfuraldehy&e In presence of thiocyanates,Abhandl. Staatuniv* Saratov Chem. 1: 113 (1936)C.A. 3IS 6995 (1937)

49

3*K Tan Q«, D. L.L*usage da furfural comma agent analytique.Congr. phana. (liage, 193*0 1935* 168 (1935)Chsmle and Industrie 35* 1051 (1935)

35* Vavruch, I.Oi« dependence of the polarographlc diffusion current on the viscosity in concentrated solutions of saccharose. Collection Czechoslov. Chem. Ccsnun. XII No. 7-8s 434-5 (1947)

36. Vogel, 1, V.Uber die absorptionsspectren elnlger salze der metalle der elsengruppe und lhre auvendung In der analyse.Bear. 8s 1533 (l$75)

37. Vogel, H. W.Spectroskopi sche notlzen.2 . Uber die erkennung des kobalts neben elaen und nickel.Ber. 12s 2313 (1879)

3 8. Voaburgh, Warren C. and Cooper, Gerald B.Spectrophotametric identification of complex ions in solution.J . An. Chem. Soc. 63s 437-**£ (1941)

39. West, Philip W. and Amis, Edvard S.Bet action of palladium using pararosanlline hydrochloride.Ind. Eng. Chem., Anal. Ed. 18s 400-2 (1946)

to. Young, B. S. and Ball, A. J.Colorimetric determination of cobalt with ammonium thiocyanate.Ind. Eng. Chem. Anal. Ed. 18: 264-6 (1946)

«« *v •»(otilt) 9*titT t©t crrra) **■*& •■*0 •#

*A(s«MtSMwci>a « t N n w iw mmmmkmmm jp»

■» '| ‘v m m h h h i n •*

VITA

Charles Coses ds Vrlss was born In Wheeling* West Virginia* on June 27* 1919* the second son of Gosse Bote and Ruth Winchester de Vries. Slementary education was received In the public schools of West Virginia, fie graduated from Ceredo-Xenova High School, Kenova,Vest Virginia* in May, 1937.

The following September, he entered Marshall College and after two years of study, transferred to West Virginia University.Upon graduation with a Bachelor of Arts Degree in June* 19^1* he accepted a position with the American Viscose Corporation.

Be terminated his association with this company on February 13* 19^3 upon entering the Army of the United States. After serving in the Medical Corps and Ordnance Department, he was honorably discharged on February 10* 19^6.

In the same month* he entered Louisiana State University Graduate School and served as a graduate assistant during the fall tem of 19h6-h7* From February, 19*1-7 to June, I9L9 he served as a research assistant.

On August 20, 19^7 he was married to Laura Brown Lynch of Baltimore, Maryland*

In June* 19td he received the Master of Science Degree from Louisiana State University and he is now a candidate for the degree of Doctor of Philosophy In Chemistry.

51

EXAMINATION AND THESIS REPORT

Candidate: CbmrXmm Goese de TrlM

Major Field: C ta s io tx y

Title of Thesis: A S'tndy o f tbi Tcgtl Reaction for the Determination of Cbbalt

Approved:

Date of Examination:

________Mny II, 19>9

Ia J. u Jj u ^Ma/>r Professor and Chairman

Dean of the Graduates School

EXAMINING COMMITTEE:

^ Q > . _______

^ __________