13 Chapter 4shodhganga.inflibnet.ac.in/bitstream/10603/90383/13/13_chapter 4.pdf · The rate of precipitation, as is well established is governed by various factors such as solubility

172

Chapter – 4

Discussion

The Kinetics is a branch of science which deals with rate and

mechanism of chemical reaction .Literature survey reveals that the

kinetics of oxidation of organic compounds have been studied by

many researchers (48–52), survey also reveals that less work have

been done in inorganic reaction mechanism but very less work has

been carried out in the field of precipitation reactions.

For the present study, we have taken a definite amount of

solid sodium thiosulphate which is treated with hydrochloric acid

solution. The solution becomes turbid, due to the formation of

Sulphur particles. The reaction takes sufficient time; therefore it

can be successfully studied by using nephelometry. The principle

of nephelometry is based on scattering of light. The nephelometer

was calibrated using formazine solution. The rate of precipitation,

as is well established is governed by various factors such as

solubility product, rate of nucleation; type of salt formed, solvent

used, temperature, etc.

The reaction of sodium thiosulphate with hydrochloric acid

is a precipitation reaction, and stoichiometry of reaction is

Na2S2O3 + 2HCl 2NaCl + SO2 + H2O + S

173

The probable mechanism of the precipitation reaction can be

given as follows:

(1) 2HCl 2H + 2Cl

O O O O H

Na S S Na Na S S Na

O O

OH

Na SO2 S Na

H OH2 Na SO2 S + Na Cl O

Na S S + NaCl + H2O

O Cl

NaCl + SO2 + S

Sodium thiosulphate and hydrochloric acid were allowed to

mix in definite proportion. The NTU reading at various time

intervals were recorded and it was observed that NTU reading

increases with the increasing concentration of sodium thiosulphate.

By using first order rate expression values of rate constant

were calculated. For the determination of rate constant, readings

174

corresponding to initial concentration was taken as

[(NTU)∞ – (NTU)0] and reading corresponding to remaining

concentration of reactant was taken as [(NTU) ∞ – (NTU)t].

A graph of log a / a – x Vs time was plotted which passes

through origin, which shows first order reaction with respect to

concentration. The slope of line is used to calculate rate constant

values for different concentration of sodium thiosulphate.

The variation of rate constant with concentration of sodium

thiosulphate shows a linear dependent.

Table: 4.1

Variation of rate constant with [Na2S2O3]:

[HCl] (M)

[Na2S2O3]

1.343 x 10– 2M k Sec–1

[Na2S2O3]

2.686 x 10– 2M k Sec–1

[Na2S2O3]

4.029 x 10– 2M k Sec–1

0.1 2.3 x 10– 3 2.9 x 10– 3 14.5 x 10– 3

0.05 4.6 x 10– 3 6.2 x 10– 3 7.5 x 10– 3

0.025 6.3 x 10– 3 9.9 x 10– 3 31.5 x 10– 3

From these values it is clear that the rate of reaction

increases with the increasing concentration of the reactant. The rate

constant varies with concentration of [HCl] and [Na2S2O3]. The

values are represented in table no: 4.1.

The increase in rate of reaction with the increase in

concentration of reactants can be explain on the basis of collision

175

theory of reaction rate which says that the number of collision

increases with the increasing concentration, it is so because the

number of molecules per unit volume is increasing thereby

increasing the rate of collision among the molecules which gives

the product, and hence the rate of precipitation reactions increases.

This reaction rate is found to be of the first order kinetics.

Brijesh pare (53) and others have studied rates for the miceller

catalyzed oxidation of Ethanol which shows dependence of rate on

surfactants concentration. Pardeep K. Sharma (54) have studied

oxidation of formic acid and oxalic acid and showed that the rate of

reaction increases with the increase in concentration of these

organic acids that are dependent on concentration of reactants.

Sarju Prasad (55) and others have studied conductometric titration of

yttrium nitrate solution at concentration 0.02M Potassium

Chromate. Tareev and Baev(56) on the basis of mathematical

equation, have shown that electrical conductance is a function of

concentration and particle size of dispersed phase. In the present

work, we have studied precipitation reaction by nephelometry

where turbidity unit reading increases with concentration.

Varsha Dhariwal(57) and others have calculated rate constant

values for oxidation of unsaturated acid and have given ‘K’ values

for different concentration of crotonic acid. For 0.1mol dm–3 as

176

5.81 x 10–4 Sec–1.We have calculated ‘K’ values for 4.029 x 10–3 M

solution of Sodium thiosulphate as 1.6 x 10–3.

From the values given in table: 4.1 it has also been observed

that the rate constant increases with the decrease in concentration

of [HCl]. Zahid Amjad(58) have studied the effect of solution pH on

the crystal growth of Calcium Sulphate in the presence of polymer

by using seeded growth technique. Considerable attention has been

given to the various forms of Calcium Sulphate crystallizing from

aqueous solution. It is affected by temperature and stoichiometric

ratio of lattice ions. Sheehan and Nancollas(59) have examined the

effect of pH in the range of 6 – 9 on the growth of Calcium Oxalate

CaC2O4 in the presence of polyacrylate. It was found that the rate

of growth was independent of solution pH.

This reaction of Sodium thiosulphate and hydrochloric acid

has also been observed for the effect of salt KCl. It is observed that

with few exceptions the rate of reaction increases with increasing

concentration of salt KCl.

177

Table: 4.2

Effect of salt [KCl] on rate constant:

[KCl] (M)

[HCl] = 0.1M [Na2S2O3]

1.343 x 10– 2M k Sec–1

[HCl] = 0.1M [Na2S2O3]

2.686 x 10– 2M k Sec–1

[HCl] = 0.1M [Na2S2O3]

4.029 x 10– 2M k Sec–1

0.0 2.3 x 10– 3 2.9 x 10– 3 1.45 x 10– 3

0.1 2.2 x 10– 3 4.3 x 10– 3 1.1 x 10– 3

0.2 8 x 10– 3 5.2 x 10– 3 1.12 x 10– 3

0.3 8.9 x 10– 3 8.4 x 10– 3 0.85 x 10– 3

Krishna Chandra (60) and others have studied stability of

lyophobic colloids. According to him, theoretical expression is

ordinarily not feasible because neither there is sufficient

knowledge(61) of a number of theoretical evolution in the relation

obtained by Verwey and Overbeek(62), nor the process of

coagulation is completely devoid of any specific effect of the ions

of added electrolyte.

The reaction has been studied at different temperatures i.e.

288 K, 298 K, 303 K and ‘K’ values at these temperatures were

found to be 3.6 x 10–3 Sec–1, 4.6 x 10–3 Sec–1 and 5 x 10–3 Sec–1. It

has been observed that the rate of precipitation increases with

increasing temperature, the reason for this can be given on the basis

of molecular theory of collision of reaction rate which says that as

the temperature is increased the particles get extra energy and they

178

move faster. It means that the number of collision among the

molecules is increasing and when this collision is in a proper

orientation then the rate of formation of precipitate increases and

hence the rate is increased. When the reaction is studied at room

temperature less number of molecules passes the activation energy

barrier. This reaction of sodium thiosulphate and hydrochloric acid

is exothermic, which push some of the particles beyond their

activation energy. Because of this more number of the particles of

sodium thiosulphate becomes available to react with HCl. At

higher temperature more number of particles becomes activated

and process becomes very fast thereby increasing the rate of

reaction. B.P. Yadava(63) and others have studied that there is

increasing specific conductance and velocity of Al(OH)3 at higher

temperatures.

At different temperatures, rate constants were calculated, and

from the linear Arrhenius plot of log K Vs 1/ T, the computed

activation parameter for overall reaction were evaluated.

179

Table: 4.3

Temperature Effect:

[Na2S2O3] = 2.686 x 10–2 M

Temp K 1 / T Rate Constant k Sec–1

Log K

288 0.003472 3.6 x 10-3 -2.4437

298 0.003356 4.6 x 10-3 -2.33724

303 0.0033 5 x 10-3 -2.30103

From the values of rate constant activation energy of

reaction were calculated by using Arrhenius equation i.e.

k = Ae – E / RT

Free energy, ∆G* is calculated by using equation

∆G* = – RTlnK

Free energy values at different temperatures were calculated

and graph of ∆G* Vs Temperature was plotted which gives straight

line, slope of this line is used to calculate ∆S* values i.e. entropy

change, intercept of this line gives values of ∆H*.

Ea* = 23.51 x 102 KJ mol–1 ∆G* = 36.652 x 102 KJ mol–1

∆H* = 36.15 x 102 KJ mol–1 ∆S* = –288.859 KJ mol–1

For higher concentration, the effect of temperature is written as

180

Table: 4.4

Temperature effect

[Na2S2O3] = 4.029 x 10–2 M

Temp K 1 / T Rate Constant k Sec–1 Log K

288 0.003472 5x10-3 -2.30103

298 0.003356 5.2x10-3 -2.284

303 0.0033 10.5x10-3 -1.97881

Table: 4.5

Temperature effect

[Na2S2O3] = 5.372 x 10–2 M


288 0.003472 7.5x10-3 -2.12494

298 0.003356 10.3x10-3 -1.98716

303 0.0033 17.7x10-3 -1.75203

The temperature dependence of rate constant is responsible

for temperature of rate of reaction. Arrhenius noticed that the

magnitude of temperature effect on reaction rate was too large to

be explained in terms of only a change in the translational energy

of the reactants. Thus, for a reaction to occur, it requires more than

just a collision between the reactants.

181

Although the Arrhenius equation is used extensively to

determine the activation energies of chemical reactions, the plot of

lnk Vs 1 / T for some reactions is not linear, such non linear

behavior can now be justified, and many modern theories of

reaction rates predict that rate constant behaves like

K = a T m e –E / RT

Where a, E, and m are temperature dependent constants.

This reaction of sodium thiosulphate and hydrochloric acid

has also been observed for the effect of radiation of light. It is

noted that there is no effect of radiation on the rate of precipitation.

It indicates that precipitation is a thermal reaction and not a photo

chemical reaction.

182

Cerium Chloride:

The reaction of Cerium Chloride with Oxalic acid is a

precipitation reaction. In the present study Cerium Chloride in

different concentration was taken and it is reacted with oxalic acid.

The stoichiometry of reaction is,

2Ce +2 + 2(COOH)2 2Ce(COO)4


given as follows:

1) COOH COO + H COOH COOH + H 2) CeCl3 CeCl2 + HCl 3) COO COO + CeCl2 Ce + HCl COOH COO Cerium Chloride and Oxalic acid was allowed to mix in

definite proportion. The NTU readings at various time intervals

were recorded and it was observed that NTU reading increases with

the increasing concentration of Cerium Chloride.

By using first order rate expression, values of rate constant



183






values for different concentration of Cerium Chloride.

The variation of rate constant with concentration of Cerium

Chloride shows a linear dependent.

Table: 4.6

Variation of rate constant with [CeCl3]:

[(COOH) 2] (M)

[CeCl3]

1.352 x 10– 2M k Sec–1

[CeCl3]

2.704 x 10– 2M k Sec–1

[CeCl3]

4.056 x 10– 2M k Sec–1

0.1 8.9 x 10– 3 9.6 x 10– 3 3.84 x 10– 2

0.05 2.04 x 10– 2 5.041 x 10– 2 3.06 x 10– 1

0.025 9.2 x 10– 3 1.036 x 10– 2 2.03 x 10– 2


increases with the increasing concentration of reactant. The rate

constant varies with concentration of [(COOH)2] and [CeCl3]. The



concentration of reactants can be explained on the basis of collision


184


number of molecules per unit volume is increasing there by


the product, and hence the rate of precipitation reactions increases,

this reaction rate is found to be of first order kinetics.

Jamil Ahmed (64) have studied precipitation of sodium acetate

trihydrate and observed that the rate of crystallization was found to

increase with the relative super saturation. S. A. Chimatadar(65) and

others have calculated initial rates of oxidation of ninhydrin by

quinolinium dichromate. For the concentration 0.4 x 103 mole dm–3

the initial rate is 3.31 mole dm–3 Sec–1. In our study when cerium

chloride concentration is 1.352 x 10–2 mole then initial rate is found

to be 2.3 moles Sec–1. He also have reported order of reaction for

different concentrations of ninhydrin as, when concentration is

4 x 10–4 mole dm–3 order is one and when concentration is 8 x 10–2

mole dm–3 order is 0.67. Whereas for Cerium Chloride reaction we

have calculated order it is given in table: 4.6. Gosta Benglsson(66)

and others have reported determination of rate law by method of

initial rates using solution. Initially, containing comparable

concentration of ion (III) and ion (II) together with access of

hydroxyl ammonium. Under these conditions, reaction becomes

sufficiently slow for values of υ0 and shows that initial rate

185

depends on concentration of Fe (III) and Fe (II). S. N. Dindi(67) and

others have reported oxidation of Tellurium by Cerium and showed

it as a first order reaction. Different concentrations of Cerium (III)

also give first order kinetics.

The rate of reaction increases with the decreasing

concentration of oxalic acid, showing dependence of rate on pH of

solution. I.P. Saraswat(68) and others studied solubility of

ammonium manganese phosphate., and observed that for lower

value of pH of solution the concentration of H+ ions will be higher

and hence PO4– –ions would tend to decrease due to association,

phosphoric acid being a weak acid. Thus, both the reactions would

be forced towards the right and hence higher solubility of

compound is expected with decrease in pH. By adding free Mn++

ions in the solution the solubility of ammonium manganese

phosphate decreases as is to be expected, because with the addition

of free Mn++ ions the reaction should be forced towards left.

The reaction has been studied at different temperatures i.e.


found to be 3.6 x 10–3 Sec–1, 4.6 x 10–3 Sec–1 and 5 x 10–3 Sec–1. It

has been observed that the rate of precipitation increases with the



186







barrier. This reaction of Cerium Chloride and Oxalic acid is

exothermic, which push some of the particles beyond their


Cerium Chloride becomes available to react with Oxalic acid. At

higher temperature more number of particles becomes activated

and process becomes very fast thereby increasing the rate of

reaction. Rupal Kumbhat(69) and others have carried out oxidation

of formic acid by quinolinium bromochromate . He says that

reaction rate increases with the increase in organic acid and also

increases with the increase in temperature. He had calculated rate

constant at 288, 298 and 308 K for formic acid as 18.4 dm–3 mole–1

S–1, 38.1 dm–3 mole–1 S–1, 75.7 dm–3 mole–1 S–1 respectively. Rate

constant were calculated at different temperatures (table 4.7)

At different temperatures, rate constant were calculated, and

from the linear Arrhenius plot of log K Vs 1 / T, the computed


187

Table: 4.7

Temperature Effect

[CeCl3] = 1.352 x 10–2 M


Log K

288 0.003472 1.55 x10-2 -1.809

298 0.003356 1.58 x 10-2 -1.801

303 0.0033 1.7 x10-2 -1.769

From the values of rate constant, activation energies of


k = Ae – E / RT


R.L. Yadav and Verma(70) have reported Ceric–Cerium

oxidation of Catchechol and said that Arrhenious law was found to

be valid.

∆G* = – RTlnK






∆H* = 29.75 x 102 KJ mol–1 ∆S* = –30.2 KJ mol–1

188

M. Bala Krishnan (71) and others have calculated ∆G*, ∆S*

and ∆H* at different temperatures as 92.66 kj mole–1,–158.56 J

mole–1, K–1, 45.25 kj mole–1, respectively. Sheila Srivastava(72)and

others have reported the reaction is first order with respect to RIII

and the values of rate constant were calculated. The graph of log K

Vs 1 / T was plotted to calculate the value of ∆G*, ∆S*, ∆H* and it

is given as 56 kj mole–1 and 58 kj mole–1, 69 kj mole–1. Samir

Kumar(73) and others have studied coagulation and electrical

properties of Ceric oxide hydrosols and its conductance were

measured which was found to be 1.04 x 10–4 Ohms at 250C.

Temperature significantly affects the flocculation (74), higher

temperature adversely affect the flocculation as evidenced by lower

settling rates at higher temperature. Variation in temperature alters

intrinsic viscosity of the polymer due to which settling rate also

changes.

Table: 4.8

Temperature effect

[CeCl3] = 2.704 x 10–2 M


288 0.003472 3.40 x10–2 -1.46852

298 0.003356 3.47 x10–2 -1.45967

303 0.0033 3.8 x10–2 -1.42022

189

Table: 4.9

Temperature effect

[CeCl3] = 4.056 x 10–2 M


288 0.003472 2.83 x10–2 -1.54821

298 0.003356 1.6 x10–1 -0.79588

303 0.0033 1.65 x10–1 -0.78252


for the temperature of rate of reaction. Arrhenius noticed that the

magnitude of temperature affect on reaction rate was too large to


of the reactants. Thus for a reaction to occur, it requires more than

just a collision between reactants.





reaction rates predict that rate constant behaves like



190

This reaction of Cerium Chloride and Oxalic acid has also

been observed for the effect of radiation of light. It is noted that

there is no effect of radiation on the rate of precipitation. It

indicates that precipitation is a thermal reaction and not a photo

chemical reaction.


been observed for the effect of salt KCl. It is observed that with

few exceptions the rate of reaction increases with increasing


Table: 4.10

Effect of salt [KCl] on rate constant

[KCl] (M)

[(COOH) 2] = 0.1M [CeCl3]

1.352 x 10– 2M k Sec–1

[(COOH) 2] = 0.1M [CeCl3]

2.704 x 10– 2M k Sec–1

[(COOH) 2] = 0.1M [CeCl3]

4.056 x 10– 2M k Sec–1

0.0 3.84 x 10– 2 8.9 x 10– 3 9.6 x 10– 3

0.1 1.28 x 10– 2 9.67 x 10– 3 1.26 x 10– 2

0.2 1.31 x 10– 2 1.70 x 10– 2 1.28 x 10– 2

0.3 2.99 x 10– 2 4.49 x 10– 2 1.47 x 10– 2

Ammonium molybdate(75) solution was coagulated by

thorium nitrate and mixed with non electrolyte this mixture was

studied by using turbidimeter. And variation in turbidity with time

was followed by reading the absorbance at intervals. He reported

that turbidity is directly proportional to the decreasing percentage

191

of transmittance. He plotted the graph of decreasing percentage

transmit tens Vs Time and the graph showed rise in turbidity with

time. By these studies he reported that the mechanism of slow

coagulation of molybdenum blue solution by thorium nitrate is the

same in presence and absence of electrolyte which indicates that

there is no effect of electrolyte on coagulation process. Mukhtar

Singh(76) and others have studied coagulation of nickel hydrous

oxide solution. He has plotted 1 / c – a against Time and it is a

straight line graph.


been observed for the effect of radiation of light. It is noted that

there is no effect of radiation on the rate of precipitation. It


chemical reaction.

192

Strontium Chloride:

The reaction of Strontium chloride with Sulphuric acid is a

precipitation reaction. In the present study I have taken Strontium

chloride in different concentration was taken and it was reacted

with Sulphuric acid. The stochiometry of reaction,

Sr+2 + SO4-2 SrSO4


given as follows:

1) H2SO4 H + HSO4 2) SrCl2 + H HCl + SrCl 3) SrCl + HSO4 HCl + SrSO4

Strontium Chloride and Sulphuric acid was allowed to mix

in definite proportion. The NTU readings at various time intervals


the increasing concentration of Strontium Chloride.








193


values for different concentration of Strontium Chloride.

The variation of rate constant with concentration of

Strontium Chloride shows a linear dependent.

Table: 4.11

Variation of rate constant with [SrCl2]

[H 2SO4] (M)

[SrCl 2]

2.1028 x 10– 2M k Sec–1

[SrCl 2]

4.2056 x 10– 2M k Sec–1

[SrCl 2]

6.3085 x 10– 2M k Sec–1

0.1 9.5 x 10– 3 12.3 x 10– 3 24.4 x 10– 3

0.05 7.5 x 10– 3 12.8 x 10– 3 14.0 x 10– 3

0.025 5.6 x 10– 3 8.9 x 10– 3 10.1 x 10– 3



constant varies with concentration of [H2SO4] and [SrCl2]. The








194



Octakar Suhnel(77) have studied precipitation of Strontium

Sulphate. In this work, they have studied precipitation, growth and

nucleation of Strontium Sulphate crystals in super saturated

solution. He showed that this reaction is a second order kinetics

with respect to concentration and temperature. The difference

between the study carried out by Octakar and present work is that,

when Sulphuric acid is allowed to react with Strontium chloride

precipitation occurs which follows the first order kinetics in present

experimental condition .Dr. Octakar studied the precipitation of

Strontium Sulphate from the aqueous solution without seeding

under super saturation condition.

F. Johns (78) have studied the mechanism of nitrolotriacetic

acid (NTA) in which they observed interaction of Barium Sulphate

with (NTA) which enhances the precipitation of Barium Sulphate.

The reaction of Strontium Chloride and Sulphuric acid has

also been studied for effect of salt KCl. It is observed that with few

exceptions the rate of reaction increases with increasing


195

Table: 4.12


[KCl] (M)

[H 2SO4] = 0.1M [SrCl 2]

4.2056 x 10– 2M k Sec–1

[H 2SO4] = 0.1M [SrCl 2]

6.3084 x 10– 2M k Sec–1

[H 2SO4] = 0.1M [SrCl 2]

8.4111 x 10– 2M k Sec–1

0.0 12.3 x 10– 3 24.4 x 10– 3 20.2 x 10– 3

0.1 1.22 x 10– 2 9.1 x 10– 3 3.2 x 10– 3

0.2 8.2 x 10– 3 11.1 x 10– 3 10.1 x 10– 3

0.3 8.21 x 10– 3 7.1 x 10– 3 3.15 x 10– 2

The reaction has been studied at different temperature i.e.


found to be 2.9 x 10–3 Sec–1, 3.9 x 10–3 Sec–1 and 11.5 x 10–3 Sec–1.

It has been observed that the rate of precipitation increases with the









barrier. This reaction of Strontium Chloride and Sulphuric acid is

exothermic, which push some of the particles beyond their

196


Strontium Chloride becomes available to react with HCl. At higher

temperature, more number of particles becomes activated and

process becomes very fast thereby increasing rate of reaction.

At different temperatures rate constant were calculated, and



Table: 4.13

Temperature Effect

[SrCl2] = 2.1028 x 10–2 M

Temp K 1 / T Rate Constant

k Sec–1 Log K

288 0.003472 2.9 x 10-3 -2.5376

298 0.003356 3.9 x 10-3 -2.40894

303 0.0033 11.5 x 10-3 -1.9393

From the values of rate constant activation energy of


k = Ae – E / RT


∆G* = – RTlnK

Free energy values at different temperature were calculated


197




∆H* = 32.40 x 102 KJ mol–1 ∆S* = –86.66 KJ mol–1

Vidhya Sagar(79) and others have carried out conductometric

investigation of thorium soaps at different temperatures .They have

studied butyrate soap at 400C, 500C and 600C free energy values at

these temperature were calculated and it is given as 40.032KJ mol-1

41.445 KJ mol-1, 43.004KJ mol-1.

D.R. Srivastava(80) and others have studied specific

interaction of m-dinitrobenzen with naphthalene and they have

calculated enthalpy at different temperatures i.e. 25.40C, 30.20C,

35.60C these values are 1760 Cal, 1746 Cal, 1652 Cal respectively

For higher concentration, the effect of temperature is written as:

198

Table: 4.14

Temperature effect

[SrCl2] = 4.2056 x 10–2 M


288 0.003472 3.91 x10-3 -2.40782

298 0.003356 4.8 x10-3 -2.31876

303 0.0033 13.3 x10-3 -1.87615

Table: 4.15

Temperature effect

[SrCl2] = 6.3084 x 10–2 M


288 0.003472 10.8 x10-3 -1.96658

298 0.003356 12.2 x10-3 -1.91364

303 0.0033 20.2 x10-3 -1.69465





of the reactants. Thus for a reaction to occur, it requires more than


199





reactions rates predict that rate constant behaves like



This reaction of Strontium Chloride and Sulphuric acid has

also been observed for the effect of radiation of light. It is noted

that there is no effect of radiation on the rate of precipitation. It


chemical reaction.

200

Silver Nitrate:

The reaction of Silver Nitrate with hydrochloric acid is a

precipitation reaction. In the present study Silver Nitrate was taken

in different concentrations and it was reacted with hydrochloric

acid which gives precipitate. The stochiometry of reaction is,

Ag+ + Cl– AgCl


given as follows:

1) HCl H + Cl 2) AgNO3 + H HNO3 + Ag 3) Ag + Cl AgCl

Silver Nitrate and Hydrochloric acid was allowed to mix in a

definite proportion. The NTU readings at various time intervals


the increasing concentration of Silver Nitrate.






201




values for different concentration of Silver Nitrate.

The variation of rate constant with concentration of Silver

Nitrate shows a linear dependent.

Table: 4.16

Variation of rate constant with [AgNO3]:

[HCl] (M)

[AgNO3]

1.9623 x 10– 2M k Sec–1

[AgNO3]

3.9246 x 10– 2M k Sec–1

[AgNO3]

5.8869 x 10– 2M k Sec–1

0.1 0.5 x 10– 2 1.45 x 10– 2 2.51 x 10– 2

0.05 2.2 x 10– 2 4.07 x 10– 2 9.9 x 10– 2

0.025 2.9 x 10– 3 6.8 x 10– 3 8.7 x 10– 3



constant varies with concentration of [HCl] and [AgNO3]. The


M. K. Mishra(81) and others have studied oxidation of

polyvinyl alcohols by benzyl triethyl ammonium chlorochromate

and have calculated K value for different concentration of alcohols

202

as 0.1 mol dm–3, 0.2, 0.4, at 298 K as 13.7 S–1, 27.65S–1, 55.1 S–1,

respectively.









Harkanwal Singh (82) and others have studied precipitation

reaction of barium chloride to give Barium molibdate by using

simple precipitation study and weight of this precipitate was

determined. During coagulation of Silver Chloride (83) with the

electrolytes of varying valancies observed that the adsorption was

high in stable region and vice versa. Dr. Banargea(84) have carried

out kinetics study of inorganic reactions. He used

spectrophotometric method for the determination of order of

reaction. Measurement of rate at different acid concentration

indicates that following expression holds goods.

Rate = K abs [Complex] [H+]

203

This reaction of Silver Nitrate and Hydrochloric acid has

also been observed for the effect of salt KCl. It is observed that

with few exceptions the rate of reaction increases with increasing

concentration of salt KCl. Flocculation studies of ferric vanadate

was carried out by Krishna Raina(85) and others. They observed

these by extinction measurement, and stated that the changes take

place with step wise addition of electrolyte. In the beginning there

is no change in extinction.

In the present study effect of salt on the precipitation

reaction is given table no: 4.17.

Table: 4.17


[KCl] (M)

[HCl] = 0.1M [AgNO3]

1.9623 x 10– 2M k Sec–1


3.9246 x 10– 2M k Sec–1


5.8869 x 10– 2M k Sec–1

0.0 0.5 x 10– 2 1.45 x 10– 2 2.51 x 10– 2

0.1 1.2 x 10– 3 2.5 x 10– 3 2.4 x 10– 3

0.2 0.92 x 10– 3 6.9 x 10– 3 4.8 x 10– 3

0.3 3.2 x 10– 3 2.3 x 10– 3 2.5 x 10– 3

At different temperatures rate constant were calculated, and



204

Table: 4.18

Temperature Effect

[AgNO3] = 1.9623 x 10–2 M


Log K

288 0.003472 7.5 x 10-3 -2.1249387

298 0.003356 8.5 x 10-3 -2.0705811

303 0.0033 2.2 x 10-2 -1.6575773

From the values of rate constant activation energies of


k = Ae – E / RT


∆G* = – RTlnK






∆H* =35.50 x 102 KJ mol–1 ∆S* = –28.93 KJ mol–1

Kavita Chawan(86) and others have carried out studies for

aliphatic aldehyde by benzyltriethylammonium chlorochromate

205

and calculated values for ∆G*, ∆S*, ∆H*, as 92.6 0.6, KJ mol–1

– 94 2 J mol–1 K–1, 64.6 0.7 KJ mol–1.

For higher concentration, the effect of temperature is written as:

Table: 4.19

Temperature effect

[AgNO3] = 3.9246 x 10–2 M


288 0.003472 8.5 x 10-3 -2.07058

298 0.003356 8.52 x 10-3 -2.06956

303 0.0033 15.6 x 10-3 -1.80688

Table: 4.20

Temperature effect

[AgNO3] = 5.8869 x 10–2 M


288 0.003472 3.2 x10-3 -2.49485

298 0.003356 1.4 x10-2 -1.85387

303 0.0033 1.65 x10-2 -1.78252




206


of the reactants. Thus, for a reaction to occur, it requires more than






reactions rates predict that rate constant behaves like



This reaction of Silver Nitrate and Hydrochloric acid has

also been observed for the effect of radiation of light. It is noted

that there is no effect of radiation on the rate of precipitation. It


chemical reaction.

207

Induced Reaction:

All the permanganate oxidations are usually complicated

because of different oxidation state of Mn (+7, +6, +5, +4, +3, +2),

that can participate in the reaction. In induced reaction, each

species has its own induction factor (IF), theoretically it is possible

to calculate it by using an equation

Where Ai --- oxidation state of intermediate of the actor.

Af ----final oxidation state of actor.

A0 ----initial oxidation state of actor.

By using above equation we can predict the probable

species, which can induce the reaction. The species with their

theoretical induction factors are given in the following table.

Table: 4.21

Manganese species of varied oxidation states with their induction

factors.

I. F

Mn+6 4.00

Mn+5 1.50

Mn+4 0.66

Mn+3 0.25

Ai – Af IF = A0 – Ai

208

It is observed that if the oxidation of Ce+3 is carried out in

the presence of oxalic acid, permanganate is consumed in access of

the amount required by Ce+3. Thus the over consumption of

permanganate which was observed here is due to an induced

oxidation of oxalic acid involving and produced in the

permanganate – Ce+3 reaction.

The induced reaction can be characterized by the induction

factor i.e. the ratio of oxidation is equivalently consumed by the

equivalents of the acceptor and the inductor, the induction factor

determine under varied experimental conditions are given in

different table(4.21).

The induction factor approaches to the value of 0.25 with the

increasing concentration of oxalic acid and it decreases rapidly in

other cases where no induced oxidation reaction was observed.

In the absence of oxalic acid, Ce+3 reduces permanganate ion

very rapidly to a mixture of Mn+3 and Mn+4, the presence of oxalic

acid in the reaction system will reduced both Mn+3 and Mn+4 to

Mn+2 as no evidence regarding the formation of Mn+4 was observe.

It is clear that whatever amount of Mn+4 is formed through either

this disproportionate. If Mn+3 are considered to be the end product

in acid condition employed in the reaction, these are not sufficient

209

to keep Mn+3 intact in the solution. Thus, as soon as it is formed, it

disproportionate to Mn+2.

The induced oxidation reactions have also been studied in

the presence of acceptor Sn+2 and Cu+2. It has been observed that

induction factor reaches to the maximum value of 0.25 which

indicates the presence of Mn+3 species in the reaction. The Mn+3 in

the system will not be stabilizing. As soon as it is found it will

immediately disproportionate to Mn+2 and Mn+4. However, it is

experimentally observed that with the solution after titration it

turns to yellow orange colour precipitate.

Effect of Salt:

The effect of salt such as sodium nitrate and Zinc Sulphate

was studied to understand the role in the characterization of

induced reaction. The induction factor was found to be 0.073

incase of sodium nitrate and 0.12 in case of Zinc Sulphate under

similar condition increasing induction factor shows following order

IF (NaNO2) < IF (ZnSo4)

When Cerium is used as an inductor then the induction

factor without the presence of the salt was found to be 0.08 and

when salt is used in the same oxidation reaction then the induction

factor is found to be 0.73 for NaNo2 and 0.12 for ZnSo4 which

210

clearly indicates that there is not much effect on induced oxidation

in the presence of salt.

211

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13 Chapter 4shodhganga.inflibnet.ac.in/bitstream/10603/90383/13/13_chapter 4.pdf · The rate of precipitation, as is well established is governed by various factors such as solubility