The reduction waves of nickel ion in some supporting electrolytes

JOURNAL

THE

REDUCTION

OF

ELECTROANALYTICAL

WAVES

OF

CHEI\IISTRY

NICKEL

ION

IN

3=3

SOME

SUPPORTING

ELECTROLYTES T. TAK4HASHI Insfifzcfe

of

Industrial

rUI;D

H. SHIRA41

University

Science,

of

Tokyo\(Jupan)

(Revised manuscript received September

Igth,

1960)

INTRODUCTION

Studies on the reduction wave of mckel ion in perchlorate as a supporting electrolyte have shown that it consists of one wave, whose wave height is independent of the concentration of perchlorate. R_ H_ SANBORN~ reported that the wave height in the reduction of nickel ion depends upon the concentration of an electrolyte such as sodium chloride or potassium chloride, and concluded that this result was due to the formation of Ni(1) ion Furthermore, A_ A. VLCEK' considered the reduction wave of nickel in sodium chloride to be accompanied by a kinetic current_ The present paper shows that the reduction waves of nickel ion in potassium nitrate, potassium bromide and potassium sulfate, as well as potassium nitrite, depend on the concentration of the supporting electrolyte,

and

that

except

in the case

of potassium

nitrate,

two

waves

are formed.

APPARATUS

The details of d-c. and a-c. polarographs have already been reported3.4. voltage of IO mV was superimposed on the applied d-c_ voltage, and the

The a-c. standard

L

I Fig_

I_

D.c_

polarograms

of (a),

0.5

I

-QS

I mM 32

I -07

I -CL6

nickel KNOJ;

E (V ion (b),

vs. N.CE_,

in potassium 1-0

AI

KNOJ;

30;)

nilkIte (c),

1.8

at various COncen~ationS (30°) M

]_~EZeciroannl_

IaO,. Chemr,

3 (19611 313-319

:

T.

314

TAKAH4SH1,

H_

SHIRAI

capacity (C,) was 0.3 PF. An agar-agar bridge connected the reference electrode [I iV calomel) and the polarographic cell, from which oxygen was removed by passing hydrogen. The dropping mercury electrode used had the following properties: m = 2.77 mg/sec, t = 3-6 set, (--1.2 V ?IS_N.C.E. in 0.5 M potassium nitrate)_ Potassirim

nitrate

as a sz+portimg

electrolyte

The reduction wave pf nickel has one wave in 0.5 M potassium nitrate, having a half-wave potential at --I-OS V (300)_ Figure I shows the d-c. polarograms of I mM nickelionin potassium nitrate at various concentrations_ The wave height decreases with increasing potassium nitrate concentration, and isindependentofthe addition ofo_o05~/~ gelatine. Figure2 showsthea.c_ polarograms of nickel ion in both the presence and absence of dissolved oxygen_ The two wave polarograrn, registered in the presence of dissolved oxygen, changes to a one wave

E PJ vs. mercury

poo~,

JO-)

Fig. 2. A-c. polarograms of IO mM nickel ion in I &I potassium nitrate in the presence or absence of dissolved nsvgcn ; (a),in the presence of oxygen; (b), in the absence of oxygen.

Fig.

=J_ _Relationsbip

between

the

wave

height of r m&T nitrate.

nickel

ion

J_ EZectroanaZ_

potassium

Chem_.

3 (1961)

313-xzo

REDUCTION

WAVES

when the dissolved oxygen

polarogram

OF

NICk-EL

is removed.

The

3=5

of this wave

disappearance

is presumed to be due to the reduction of Ni(OH)+ or Ni(OH)z formed by reaction with OH- ion,whichisproducedbydissolvedosygen on thesurface oftheelectrode. Figure3

givestherelationshipbetweenthewaveheightandI/hin

nitrate. The

graph

does

kinetic currentinthe Potassium

bromide

not

pass

through

the

r.S Mpotassimn

origin, indicating

the presence

of a

limiting current. as

a szcp~orti~~g

eZectroLyte

The shape of the reduction wave of nickel ion changes withthe concentration of potassium bromide used as a supporting electrolyte_ InFig.4,thed.c.polarogramshowstwo distinctwavesino.SMpotassiumbromide, but the secondwave seems to disappear at a concentration of r.S M, asisshown by (c)_ The half-wave potential of the first wave is -r-o7 V (30°j in 0-5 M potassium bromide. Thesecondwavealsodisappearsifo.oo~o/ogelatineisaddedtothesupporting

L 18 -

- 0.8

Fig-

4. D-c.

polarograms 0.8

M

- 10

of I mM nickel KBr containing

-1.2 E (V

5-

A C. POlarOgrams

of

N.CE.,

vs.

mercury

-1.6

-18

27’)

ion in potassium o.oo~~/~ gelatine;

E (V Fig.

- 1.4 VS.

bromide I (a), in 0.8 (c), in r-8 M KBr.

poop,

_W

I
(b).

300)

IO III&I nickel ion in 0.8 A&potassium bromide: of oxygen; (b). in the absence of oxygen.

(a),

in the

prsence

in

3x6

T_ TAKAHASHI,

KL SHIRAI

electrolyte solution, as can be seen from Fig- g(b)_ Similarly, the second wave was confirmed in the presence of dissolved oxygen, which it disappeared, as can be seen from Fig. 5_ Figure

6 gives

the relationship

in a d-c_ polarogram

of I mM

between nickel

line (b) does not pass the origin, more, the elxistence of a kinetic

the

wave

ion in 0.8

height

of the

A4 potassium

indicating the presence current was also found

appearance of the in the absence of first

wave

bromide,

of a kinetic in the d-c.

and

in which

@ the

current Furtherpolarogram (c) of

nickel ion in 023 M potassium bromide containing o_oo~~/~ gelatine, (as shown in Fig. 6), and in r-8 M potassium bromide (not shown in the Figure). But the line expressing the relationship between the total wave height and r//t passes through the origin

(line (a)), showing

that

the limiting

1 Fig. 6. bromide

Relationship (~7~) : (a).

3

the

presence

7_ D-c_ in o-45

polarograms M &S04;

of I m_ii (b). in o-3

M

of

(V

VS_

diffusion

rate.

277.j

of I m&E nickel xvaves; (b). the o.oo~~/~

ion first

and vh in o-8 ~l:ipotasr;iun~ wave; (c), the first wave in

gelatine.

-14 N.C.Ej

by the

9

N-C-E.,

-1.2 E

Fig(4.

vs.

height second

-113

is controlled

5

E (V

between the wave sum of the first and

current

-16 27”

-1.6

I

nickel ion in potassium sulfate at I(,SO4; (c). in o-3 N J&SO, con~g

various

concentrations: gelatine.

0_005~/~

RJZDUCTION

Potizssit4m sulfa&9 as a szcp$wting

WAVES

OF

3=7

NICKEL

eZectroZyte

Figure 7.shows the d.c. polarogram of I m&f nickel ion in o-45 N (a) or 0.3 A4 (b) potassium sulfate. The shape of the wave changes with the concentration of potassium sulfate, and the addition of o_o05~/~ gelatine makes the second wave disappear, as the polarogram (c) in 0.3 M potassium sulfate shows_ The half-wave potential .is --I.IZ V (30~) in 0.3 M potassium sulfate_ The a-c.. polarogram of nickel ion in the presence of dissolved oxygen is given in Fig. 8, which-shows two waves, the second wave disappearing in the absence of dissolved oxygen.

I

-1.2 E
Fig.. 8.. Ax.

I

-1-4 Yz. mercury

I

I -16

pool.

- 1.8 30”)

polarograms of IO m&T nickel ion in 0.5 M potassium sulfate: (a). in the presence dissolved osygen; (b). in the absence of dissolved oxygen.

of

Fig. g_ Relationship between the wave height of I miW nickel ion andvjz in 0.3 MT potassium sulfate _ (a), sum of the first and second waves; (b), the first wave; (c), the first wave in the presence of 0.005 a/- gelatIne_

The relationship between the wave height of the first wave and pz in the d-c_ polarogram in 0.3 M potassium sulfate is shown in Fig- g, in which the line (d) does not pass through the origin, indicating the presence of a kinetic cm-rent.. Smce.line (c) also does not pass through the origin after the addition of o.oo5°/o gelatine, the yave: height is partly dependen L on kinetic current- But the limiting current containinff:

T_ TAKAHASHI,

3rS the first znd

expressing

second

waves

is controlled

the relationship between

H.

by

the total

SHIRAI

the diffusion rate, because wave

height

andvlc

the

linh

passes through

(a) the

origin_

The d-c. polarogram of nickel ion in o-5 M and I M potassium nitrite gives two waves as shown in (a) and (b) in Fig_ IO, but xtith an increase in the concentration of potassium uitrite, the first wave height seems to increase and the second wave height

decreases, although

only slightly_

The

---o_S5 V (307andthatofthesecondwave--1.09 The latter potentials equals the half-wave

half-wave V

potential

potential ofthefirstwaveis

(30°)ino.5 Mpotassiumnitrite. of Ni(HzO)e"+.

6

-0.6

Fig-

IO-

D-c-

- 0.6

E

polarograms

I

E (v Fig-

II_

Ax_

tv

of I mM niclcel ion in IL1 I
polarograms

of

IO m&1 oxygen;

YS_

N.CE.,

30°)

potassium nitrite:(a),in 0.5 1w KNO.; containing

vs. mercu~-y

o OO~~/~

pod

(b).

in

gelatine.

)

nickel ion in I M pot&urn nitrite: (b). in the absence of oxygen_ J_ Ekctroawal.

(a),

Chem_.

in the

presence

3 (1962)

of

313-320

REDUCTION

The

a-c. polarogramin

I M

potassium

WAVES

OF NICKEL

nitrite containing

3=9 dissolvedoxygenis

given

Fig. II, which shows three waves in the presence of dissolved oxygen, although the third wave disappears after removal of the oxygen. It is not certain that the first wave is controlled by the diffusion rate-because it is difficult to determine the rela-

Fig.

I?_ Relationship

between

the wave height

of I m&1 nickel ion and I/k in 0-5 potassium (279.

nitrite

tionship between the wave height and V?z,as the firstwave approaches the second wave. But the total wave height obtained by combining the firstand second waves passes through the Orion, in~catingthat the total limiting current is controlled by the diffusion rate, as can be seen from Fig. IZ. DISCUSSION

Ofthetwo waves of nickelionin potassium sulfate andpotassium bromide, the first wave accompanies the kinetic current. Therefore, it is considered that the reduction ofnickelionistheelectrodereaction,forcompo~dswhichareinmutua2equllrbrium. Here, the firstwave equals the half-wave potential of Ni(H&)$+, so the firstwave is probably due to the reduction of Ni(HzO)G'+. But the second wave appearing in thepresenceofdissolvedoxygenoccursatapotential---o_zVmorenegativethanthat of the first wave, and it disappears in the absence of dissolved oxygen, so that it is perhaps due to the reduction of Ni(OH)+ or Ni(OI-E)zformed between nickel ion and OH-ion, which is producedby reduction of the dissolved oxygen. The second wave appearinginthe absence of dissolved ox3Tgerroccurs at a potential ~_4to -0-5 V morenegativeth~thatoffhefirstwave,sothatitisprobablynotduetothe reduction of any compound co-ordinated by an OHgroup_ But such a second wave is consideredtobeduetothereduction ofacompoundco-ordinatedby SOa- or Br-ions of the supporting electrolyte, because the second wave height depends upon the concentration of the supporting electrolyte_According to I. M. KOLTHOFF AND J- JLINGANE”, nickel ion exists as Ni(H20)E "+in potassiumnitrate solution_ But the presentstudysho~vedadecreaseinthe~vaveheightofnickelionwithincreased(o.5 n/l--+ J_ EbckxztlaE.

Chcnz.. 3 (1962)

313-320

T. TAKAHASHI,

320

H.

SHIFLTI

I Al->r.S _Mr) potassium nitrate concentration, and a combination of kinetic current into its wave height_ Therefore, it is evident that in potassium nitrate there is not but also a compound coordinated by NO3;-_ These compounds are only Ni(HzO)G+. mutually in a state of equilibrium, the latter compound not being reduced until the applied

d-c_ voltage

reaches

the

potential

of the

final

increase

current. In potassium nitrite, nickel ion exists as two complexes, the complex co-ordinated by NO?-_ The first wave is caused

of the

polarographic

i.e., as Ni(H2O)s”+ and by the reduction of the

latter and the second wave by the reduction of Ni(HsO)s~~. The authors have considered the results of R. H. SANSORN~ regarding the interdependence of wave height and the concentration of tbe supporting electrolyte, as follows. Nickel ion perhaps occurs as Ni(H&)6”+, even in large concentrations of perchlorate, because perchlorate ions do not complex with metallic ions. In sodium chloride solution, two complexes, i.e., Ni(HsO)63+ and a compound co-o&mated with Cl- co-exist, and the former may be more reactive to the reduction than the latter_ Therefore, the concentration of r\ri(.H,O).z ‘+ decreases with increase of Cl- ion, resulting in a lower wave height in large curring in small concentrations.

concentrations

of sodium

chloride

than

that

oc-

The reduction wave of nickel ion in potassium sulfate, bromide or nitrite shows two waves and the first wave is accompanied by a kinetic current, so that Ni(HzO)&and a compound co-ordinated with the anion of the supporting electrolyte are mutually

in a state of equilibrium,

the former being responsible for the first wave and the latter

for the second wave_ In potassium nitrate supporting electrolyte, Ni(HzO)a”” in equilibrium, and it was concluded from the half-wave is responsible for the reduction wave.

and another complex are potential that the latter

REFERENCES 1 R.

H_

-’ -4. A. 3 N.

SAXBORN ~I_CES,

SHIRAI,

3.

a T_ TAKAHASHI 5 I_ X. KOLTHOFF 1952,. p_ &36_

AND E_ F_ ORLEMANN, f_ Anz. ChemEZektrocTzezrz.. 61 (x957) xorq. Ckmz. Sut_ ~a$xz~z. 80 (1959) 609. 1435; AND E- ?+~KI. ~akmte, 3 (x958) 2~5. AND J_ J_ LIE;GAXE, Polarogmpizy.

Sac.. 78 (1956) $35~

2.

Sr (1960)

12+

Interscience

(in

Japanese).

Publishers

Inc.. FJe\vYork,