Rate of reduction of silver ions and silver complexes in solution with developers

(1)

Rochester Institute of Technology

RIT Scholar Works

Theses

Thesis/Dissertation Collections

5-1974

Rate of reduction of silver ions and silver complexes

in solution with developers

Richard Shadrach

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Recommended Citation

(2)

RATS

OF

REDUCTION

OP

SILVER

IONS

AND

SILVER

COMPLEX'S

IN

SOLUTION

WITH

DiVELOXRS

by

Richard

Shadrach

A

thesis

submitted

in

riartial

fulfillment

of

the

requirements

for

the

degree

of

Bachelor

of

Science

in

the

School

of

Photographic

Science

and

Instrumentation

in

the

College

of

Graphic

Arts

and

Photograph:/-of

the

Rochester

Institute

of

Technology

May

1974

(3)

43 7tk,

Lp

y/ cp

ACKNOWLEDGEMENTS

I

would

like

to

express

my

appreciation

to

Dr.

B.

H.

Carroll

for his

many

helpful

suggestions

and

ideas

and

the

CIA

for

providing

financial

aid.

(4)

TABLE

OF

CONTENTS

List

of

Tables

iv

List

of

Figures

v

Abstract

Introduction

1

Experimental

3

Method

of

following

silver reduction

3

Determination

of

pAg

4

Determination

of pH

4

Preparation

of

dolloidal

silver

5

Density-silver

reduced

relationship

7

ResuJts

and

Discussion

10

Rate

and silver

ion

concentration

14

Rate

and silver complex concentration

17

Change

in

concentration of reactants

21

Conclusions

25

Recommendations

for

further

investigation

27

List

of

footnotes

28

Appendix

I

29

(5)

LIST

OF

TABLES

Table

I

Table

II

Table

III

Table

IV

Table

V

Table

VI

Table

VII

Table

VIII

Table

IX

Table

X

Table

XI

Developer

Components

3

Preparation

of

Colloidal

Silver

7

Develooer

for

Density-Silver

Relationship

8

Solution A

Components

14

Change

in

Rate

with

Silver

Ion

Cone.

Solution

B

Components

15

Change

in

Rate

with

Sliver

Ion

Cone.

Change

in

Rate

with

Silver

Ion

Cone.

15

Solution

B

Components

17

Change

in

Rate

with

Silver

Complex

Cone.

Change

in

Rate

with

Silver

Complex

Cone.

18

Hydronuinone

Develooing

Agent

Solution

A

Components

21

Change

in

Rate

with

Silver

Xmolex Cone.

-'/letol

Change

in

Rate

with

Silver

Complex

Cone.

21

Metol

Develooing

Agent

Change

in

Concentration

of

Reactants

at

24

a

Density

of .8

(6)

LIST

OF

FIGURES

Fig.

I

Potentiometric

Titration

of

KBH

by

AgN03

6

Fig.

II

Density-Silver

Reduced

Relationship

9

Pig.

Ill

Density

vs.

Time

11

Hydro

-uinone

-Varying

pAg

^

1/3

Pig.

IV

Ag

vs.

Time

13

Hydro

-uinone

-Varying

pAg

Pig.

V

_-Log

Rate

vs.

pAg

Hydroquinone

16

Pig.

VI

Ag1^ _vs.

Time

^

19

Hydroquinone

-Varying

[Ag(

S03)

2~^

Fig.

VII

Rate

vs.

l^g(S03)2"^|

Hydroquinone

20

Pig.

VIII

Ag1/5

vs.

Time

r--^

22

Metol

-Varying

Ag(S03)2

Pig.

IX

Rate

vs.

Ag(SC3)2~^]

Metol

23

(7)

ABSTRACT

The

change

in

rate of reduction of silver

from

solutions

of

varying

silver

ion

and silver sulfite comolex

by

hydroquinone

and metol was studied.

The

silver

ion

concentration was varied and

the

silver complex concentration

was

held

constant.

The

rate was

found

proportional

to

the

square root of

the

silver

ion

concentration

for

development

by

hydroquinone.

The

silver complex concentrat

ion

was varied

and

the

silver

ion

concentration was

held

constant.

The

rate of reduction

increased

as

the

complex concentration

increased

for

both

hydroquinone

and metol

developing

agents,

showing

that

the

complex was

being

reduced.

The

rate

appeared

to

be

proportional

to

the

silver complex concentration.

The

reaction rate was proportional

to

the

surface area of

the

silver particle and was not

found

to

be

controlled

by

(8)

INTRODUCTION

In

physical and solution physical

development

silver

from

solution

is

reduced on

to

nuclei.

In

physical

development

silver and a

complexing

agent are

incorporated

in

the

developer.

During

solution physical

development

silver

halide

is

dissolved

by

a

complexing

agent

Introducing

silver

Ions

and silver comolex

into

solution.

The

silver

can

then

be

reduced at

the

latent

site or nuclei.

There

is

some question as

to

whether

the

silver comolex

is

providing

silver

ions

to

be

reduced or

if

the

complex

itself

is

also

being directly

reduced.

James

investigated

the

reduction of silver

from

solutions of silver

ion

and silver sulfite complexes.

For

hydroquinone

and paraphenylenediamine at a oH of about nine

he

found

that

it

was

the

silver

ion

being

reduced and not

2

the

silver complex.

Levenson

and

Twist

investigated

the

change

in

rate with a change

In

the

silver

ion

concentration

for development

by

hydro

ruinone

in

the

presence of sulfite

at a pH of

9.1.

They

could not

decide

from

their

results

If

the

silver complex was reduced

directly

or not.

They

did

determine

that

the

rate of

development

was proportional

to

(9)

of

the

silver

ion

concentration,

and

inversely

proportional

to

the

hydrogen

ion

concentration.

At

a

higher

pH or

for

more active

developing

agents

the

potential of

the

developing

agent

is

greater.

There

would

seem

the

possibility

that

the

silver complex

may

be

reduced.

This

was

investigated

for

silver sulfite complex and metol

and

hydroquinone

developing

agents.

The

conditions under vhich

the

reactions were studied

were not

Identical

to

those

that

occur

in

photographic

development.

Therefore

the

results can not

be

directly

apollcable

but

give some

Insight

as

to

what

may

be

occurring.

Colloidal

silver was present

in

the

reactions

to

initiate

the

reaction and

to

prevent an

induction

period.

The

reaction of silver

ion

being

reduced

to

silver metal

is

favorable

when calculated

from

the

redox ootential and silver

2

ion

activity/

of

the

solution _,

but

the

first

silver atom

reduced

has

the

character of a

free

radical.

It

readily

loses

Its

electron and reverts

to

a silver

ion.

For

the

reaction

to

proceed

the

silver atom must

be

stabilized

by

a conductive

mass such as a silver nuclei.

The

reactions were carried out

in

the

presence of

gelatin \h

ich

served

to

suspend

the

silver

that

was reduced

and give a closer approximation as

to

the

conditions

that

(10)

EXPERIMENTAL

Method

of

following

silver reduction:

The

rate of reduction of silver was

followed

by

mixing

the

two

solutions

in

Table

I.

Table

I

Developer

Components

Solution

A

Solution

B

Inert

gelatin

Silver

nitrate

Buffer

Sodium

sulfite

Colloidal

silver

Sodium

sulfate

Developing

agent and

sodium sulfite

Distilled

water

Both

solutions were placed

in

a constant

temperature

water

bath

and

brought

to

25

C.

'Solution

A

was

bubbled

with

nitrogen

through

a

fritted

glass

tube.

Tho

develooing

agent

was

then

added

to

solution

A

after a

few

minutes

to

prevent

oxidation at

the

high

pH.

The

reaction was started

by

adding

solution

B

to

solution

A.

Five

milliliter samples of reactant were pipetted

off at

varying

time

intervals

and added

to

five

milliliters

of

0,1

M

sodium

thiosulfate.

The

trensmittance

of

this

solution was

then

measured on a

Bausoh

&

Lomb

Spectronic

20

at

415

nanometers

corresponding

to

the

maximum absorbtion of

(11)

A

small amount of sodium sulfite was

included

with

the

developing

atrent

to

act as a preservative.

Sodium

sulfate

was added

to

eliminate

any

change

in

rate

due

tr- _a change

In

ionic

strength.

Develo'nln,?

a^ent and sodium sulfite

solutions were used within

in

six

hours

after preparation

to

prevent oxidation.

Determination

of pAg:

The

Corning

Model

12

Research

pH meter was calibrated

with standard solutions

to

measure silver

ion

concentration

using

a silver electrode.

The

standard solutions were prepared

by

precipitating

silver

bromide

and

washing

off excess

bromide

and silver

ions.

-3 -4

The

precipitate was

then

added

to

10

and

10

M.

potassium

bromide

solutions.

The

silver

Ion

concentration can

then be

calculated

knowing

the

bromide

ion

concentration

from

the

following

eiuation.

[kg\

\btF\

"

4.85

X

at

25

C.

Measurements

were made at

25

C.

end

the

following

relation was

determined,

pAg

= _{-0.01695(millivolts)}

X

9.492

Measurements

of

pAg

of

the

samples were made on

duplicate

solutions

omitting

only

the

develooing

agent.

Determination

of pH:

The

solution pH was measured with

the

Corning

Xodel

12

(12)

except

for

the

addition of silver nitrate were used.

The

range of sodium sulfite concentrations employed were checked

for

variations

in

pH

due

to

changes

in

sulfite concentrations

and none were

found.

A

change

in

pH

due

to

reaction

products was checked

for

by

measuring

the

pH as

the

reaction

proceeded.

No

change

in

pH was noticed.

Preparation

of colloidal silver:

The

colloidal silver was prepared

by

reducing

silver

nitrate with potassium

borohydride.

Moles

of silver nitrate reduced per mole of potassium

borohydride

was

determined

potentiometrically.

Potassium

borohydride

was

titrated

with silver nitrate.

The

silver

ion

concentration "/as

followed

using

the

Corning

Xodcl

12

pH meter and a silver electrode.

The

following

amount of

potassium

borohydride

was used and

corresponding

amount of

silver nitrate

to

reach

the

endooint.

(Fig.

I)

(0.019

M

KBH4)(.025

1.

)

=4.75

X

10-f

moles

(0.25

M

AgNOg) (.00186

1.

)

=

4.67

X

10

_moles

moles of silver

Q

, yts

moles of

borohydride

~

One

mole of potassium

borohydride

reacted with one

mole of silver nitrate.

This

was

important

to

know

in

preparing

the

colloidal silver so as not

to

have

an excess

of either silver

ion

or

borohydride

which would effect

the

(13)

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(14)

L-A

500

milliliter solution of colloidal silver was

prepared as

in

Table

II.

Table

II

Preparation

of

Colloidal

Silver

component volume

l'-i

Inert

trelatin

250

ml.

6.25

X

10"

LI

AgIT03

50

ml.

0,1

M

Borax

'

150

ml.

Distilled

water

45

ml.

0.038

M

KBH4

5

ml.

pH

9.3

The

solution was

heated

to

60

C.

and

the

potassium

borohydride

added.

The

potassium

borohydride

solution was

used within one

half

hour

after preparation.

There

was

a slight excess of

borohydride

after reduction when

using

these

concentrations.

This

made

the

silver

ion

concentration

very

low.

The

pAg

was measured at

6.15.

Density--

Silver

_reduced _relationsh

io:

A

calibration

in

terms

of silver reduced

anddersit;'-was

made.

Small

concentrations of silver nitrate were used and

allowed

to

be

completely

reduced

to

silver.

The

developer

formulation

in

Table

III

was used.

The

solution was prepared without

the

hydro-uinone-sulf

ite

solution and

bubbled

with nitrogen. 'The hydroquinone-_sulf

ite

solution was

then

added

to

start

the

reaction.

Two

five

milliliter samples were

taken

after ar>oroxima

tely

five

minutes.

(15)

8

other was added

to

five

milliliters

0.1

M

sodium

thiosulfate.

Transmittance

of

both

were measured and converted

to

density.

Table

III

Developer

for

Density-Silver

Relationship

component volume

final

concentration

1'i

Inert

gelatin

50.0

ml.

4$

0.1

M

Borax

25.0

ml.

0.02

M

0.2

M

NaOH

15.0

ml.

0.024

M

_4

0.0025

X

AgN03

1-10

ml.

2

X

10-2

X

10

Colloidal

silver

0.5

ml. *

2.5

X

10"b

LI

Distilled

water

to

make

total

volume

125

ml.

0.25

M

HpQ,

and

1.0

ml.

0.002

LI

0.125

Na2S03

, .

0.001

H

There

was some

destruction

of silver

by

the

thiosulfate

but

it

was proportional

to

the

amount of silver present.

This

can

be

seen

from

the

linear

plot of silver nitrate

reduced versus

density

for

both

water and

the

thiosulfate,

(Pig.

II).

Most

of

the

destruction

of

the

silver

took

place

within

the

first

few

seconds after addition

to

the

thiosulfate,

After

approximately

one minute

the

solution was stable.

Regression

analysis-was used

to

determine

the

following

equation

for

the

density

silver relationship.

Ag

, , =

2.714

X

10-4(densitv)X

2.9

x^lO-6

e

reduced

Rd=99.7%

Substituting

transmittance

for

density

the

following

relation was

found between

silver reduced and

transmittance.

,-4

ASreduced

~

2'714

X

10-4(log10(l/trans)

)+

2.

9

X

1

0

This

relation was used

in

slotting

silver reduced versus

(16)

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9

r-io

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(17)

10

RXSULTS

AND

DISCUS3ICN

It

can

be

seen

from

the

density

versus

time

curves

that

the

rate of reaction increases' as

the

reaction

proceeds.

(Fig.

Ill)

If

the

rate of reduction

is

controlled

by

the

rate of

reaction at

the

surface of

the

growing

silver

particle,

then

the

rate would

be

proportional

to

the

surface area or

o

the

square of

the

radius of

the

particle.

dm

2

C<

r

dt

where ra^mass of Ag

particle,

r=particle radius

SXnce

the

mass of a silver particle

is

proportional

to

the

cube of

its

radius,

the

square of

the

radius

is

proportional

to

the

mass

to

the

2/3

power.

2

2/3

r

CK

m

and

dm

~/

2/3

dt

<

m

Upon

integration

this

gives

1/3

, .

m. '

mQ

' =

k,

where mt=mass at

time

t,

m amass

initlaly

Since

the

mass of

the

silver

is

proportional

X

the

concentration,

the

cube root of

the

silver reduced plotted

(18)

x

;

j

T

.

iiii1- r ! ! ' '

t i "

: ' t--r""""

>

11

...

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:

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--.-i

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g.

T

b

i11 7

*'0

CO

CD

C

CD

(19)

12

eiuation

holds

for

this

reaction.

In

Xig.

IV

the

cube root of silver reduced

is

plotted

against

time

for

varying

silver

ion

concentrations.

Straight

lines

were obtained

for

most of

the

reaction.

There

was a slight

induction

period.

Levenson

and

Twist

attributed

this

to

the

small sloe of

the

The

rate

being

controlled

by

the

surface area of

the

particle

shows

that

diffusion

is

not

important

in

determining

the

2

^

4-rate of

the

reaction.

Matejec

and

TurkeviclM

concluded

that

in

diffusion

controlled reactions

the

rate

is

proportional

to

the

particle radius.

_dm_

^

dt

^

Vhich

then

fXves

the

following

equation:

mt2/3 _

mQ2/3

=

kt

The

silver reduced

to

the

2/3

power plotted against

time

should produce a straight

line

for

a

diffusion

controlled

reaction and

this

is

not

the

case.

2

Levenson

and

Twist

also

found

that

the

activation

energy

for

silver nuclei made

by

borohydride

reduction was

14.6

Kcal/mole.

This

indicates

that

the

reaction

is

not

diffusion

controlled,

since reactions

that

arc range

from

4

to

7

Kcal/mole^,

"Levenson

and

Twist

used similar silver nuclei

by

borohydride

reduction and obtained

a-size of

75

A

(20)

i

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i

! -"

1 ;

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j

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i

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X

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AC

r

Qt

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ec

)*

T(T

(21)

14

The

reaction not

being

diffusion

controlled

is

important

in

determining

the

mechanism of reaction at

the

particle surface.

Rate

and silver

ion

concentration:

The

change

in

rate with silver

ion

concentration was

Investigated.

The

following

concentrations

for

solution

A

in

Table

IV

were used.

Table

IV

Solution

A

components

Change

In

rate with silver

ion

cone.

component volume

1%

Inert

gelatin

50.0

ml.

.1

M

Borax

25.0

mi.

.2

M NaOH

15.0

ml.

Colloidal

silver

0.5

ml.

.25

M

HpQ

..1.0 ml.

.125

M

NagS03

Distilled

water

to

make

125

ml.

final

volume

of solution

A

and

B

pH

9.77

The

silver

ion

concentration was varied and

the

silver

complex concentration was

kept

constant.

This

was

done

by

varying

the

sulfite concentration and

keeping

the

silver

nitrate concentration constant.

The

concentrations

in

Table

V

were used

for

solution

B.

The

rate was expressed as

the

slope of

the

linear

portion of

the

cube root of silver reduced versus

time

plot.

The

rates

in

Table

VI

were obtained

for

changes

in

(22)

15

Table

V

Solution

B

components

Change

in

rate with silver

ion

cone

(initial)

AsN03

M

x 105

Na2S03

M

x 103

Na2S0

"

M

x 103

Na2S0

M

x IO3

2.0

24.0

1.0

136.0

2.0

40.0

1.0

120.0

2.0

80.0

1.0

80.0

2.0

160.0

1.0

0.0

Ag

+

_

(final)

S03

.

Ag^O^"3

*

P-Ag

measi

M

x 109

M

x.,105

M

x 10

13.6

21.0

2.0

7.99

4.38

37.0

2.0

8.49

1.01

77.0

2.0

9.01

0.243

160.0

2.6

9.45

""NapSO,

included

with

developing

agent

""""Pinal

cone,

calculated assuming:

all

AgN0

formed

silver complex

only

complex

formed

was

Ag(SQ

)

"5

Xuilibrium

constant =

3

_x

10

ra

te

-log-rate

.0916 .098

1.038

1.008

.057 .0568

1.244

1.246

.0324 .0331

1.49

1.48

.02 .021

1.70

1.684

Table

VI

Change

in

rate with silver

ion

cone.

PAg

7.99

8.49

9.01

9.45

Regression

analysis- _was _used _on.

the

data-in

Table

VI.

A

linear

relation was

found

between

the

pAg

and _-log

rate.

The

slope of

the

equation was .468.

AN

OVA

for

the

(23)

16

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of

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being

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.5 means

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varies as

the

square root of

the

silver concentration.

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agrees with results Levenson2 and

James

obtained.

Rate

and silver complex concentration:

The

change

in

rate with silver sulfite complex was

investigated

for

hydroquinone

and metol

developing

agents.

-The

free

silver

ion

concentration was

held

constant as

the

silver sulfite complex concentration was varied.

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was

done

by

va^ing

the

silver nitrate concentration and

calculating

the

amount of sulfite needed

to

keep

the

silver

ion

concentration constant.

The

concentrations used

for

solution

B

are

in

Table

VII.

Table

VII

Solution

B

Components

Change

in

Rate

with

Silver

Complex

Cone.

AgNO?

,

M

xlO*5

Xa2S03(initlal)Na?S03%

M

x IC3

M

x

10

6

Na

S0A

MMx

103

0.5

18.5

1.0

83.5

2.0

40.0

1.0

62.0

6.0

75.08

1.0

26.92

10.0

101.73

1.0

0.0

(final)""""

Ag+

S03

-Ag(S03)2~3

P

^measured

M

x 10y

M

x 10-5

M

x 103

4.383

18.5

0.5

8.52

4.383

37.0

2.0

8.49

4.383

64.08

6.0

8.47

4.383

.82.73

10.0

8.46

XlagSO,,

included

with

developing

agent

"'"'Xinal'

cone, calculated

assuming;

all

AgN03

formed

silver complex

only

complex

formed

was

Ag(SC3)2

(25)

18

Hydroouinone:

The

change

in

rate with a change

in

silver complex

concentration was

investigated

for

hydroquinone

developing

agent.

The

concentrations

in

Table

IV

were used

for

solution

A.

The

rates

in

Table

VIII

were obtained.

Table

VITT

Change

in

Rate

with

Silver

Complex

Cone.

Hydroquinone

Developing

Agent

[jSilver

sulfite

complex}

rate

5

x 10-4

M

.0407 .0373

2

x 10"3

M

.0442 .044

6

x 10~3

M

.052 .0534

1

x 10~2

M

.0688 .0768

The

rate

increased

with an

Increase

in

silver sulfite

complex concentration(Pig.

VI),

This

shows

that

the

silver

sulfite complex

is

beinsr

reduced.

There

was a small change

in

the

silver

ion

concentration measured

but

it

does

not

account

for

the

change

in

rate

found

assuming

the

rate varies

as

the

square root of

the

silver

ion

concentration( Tabl

e

VII).

Plotting

rate against

the

concentration of silver

sulfite appeared

to

produce a

linear

relationship(Fig.

VII).

Regression

analysis was run and

the

data

statistical^/-fit

a

linear

relationship(Appendix

I).

This

means

that

the

rate

is

proportional

to

the

silver salfite concentration.

Metol:

Metol

could not

be

studied at

the

higher

pH

because

the

rate was

too

fast

to

measure.

The

pH was

lowered

to

(26)

19

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