bab 2 potensio 1

CHAPTHER II

LITERATURE REVIEW

II.1 Basic Theory

II.1.1 Deffinition of Potentiometry

Nernst equation gives the relative potential relationship between an

electrode and the corresponding concentration of ionic species in solution.

With a reversible electrode potential measurements, the calculation of the

activity or concentration of a component can be done (Khopkar, 1990).

Picture II.1 Scheme Potentiometric

Potensiometri is a direct application of the Nernst equation by

measuring the potential of two electrodes are not polarized at zero flow

conditions. Thus, in conditions that have current zero (Khopkar, 1990).

Conditions of Ag+ on the vessel left to be determined . Vessel that

connects the middle of KCl solution contained in the saturated calomel

electrode with a vessel containing a solution of silver through the salt

bridge containing agar and NH4NO3. If a potential measuring device is

connected to two electrodes , Ag into the positive electrode , while the

saturated calomel electrode , SCE is the negative electrode. By using the

Nernst equation (Khopkar, 1990):

EAg=E Ag0 + RT

nFln ¿¿

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2,303 (RTF

) tribal is worth 0,0591 at 25°C, which should be remembered in

the calculation (Khopkar, 1990).

If the same two electrodes placed on the cylinder containing the

same solution , ( but different concentration ) and connected by a salt

bridge , the potential between two electrodes in accordance with the ratio

of the concentration.This is known as the cell concentration (Khopkar, 1990).

II.1.2 pH Measurement

Picture II.2 pH meters

For the determination of pH, made cell with electrodes that one

equilibrium with H+ ions and put into the solution under investigation.

More usually a calomel electrode. As a junction with a salt bridge or

directly enter a calomel electrode into the solution under investigation. Of

Ecell measured with a potentiometer can be obtained by E electrodes are

reversible with H+ ions, it can be determined from the pH (Sukardjo, 2013).

By using the pH=-log H+ relation, the measurement of H+ can be

simplified. For the example pH of 0,05 M based on operational pH is

(Khopkar, 1990):

pH=4,000+12 ( t−15100 )

2

jika = 0 sampai 55°C

For pH measurement, required an electrode having a reversible

response to the concentration of hydrogen ions H+. For example, a

hydrogen electrode (Khopkar, 1990):

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and if the concentration of H+ standart derived from NHE (Normal

Hidrogen Elekroda) whose concentration is 1 N, then (Khopkar, 1990) :

E sel=−0,0591 log ¿

pH=Esel0,059

1. Quinone and hydroquinone

Equimolar mixture solution of quinone and hydroquinone cause an

equilibrium that involves both electrons and hydrogen ions (Khopkar,

1990):

Picture II.3 Quinone and Hydroquinone

Kuinhidron electrodes can not be used for solutions with pH>9,0,

because hydroquinone can be neutralized by a base. Likewise,

should be avoided from the reductant and oxidant strong (Khopkar,

1990).

2. Antimony Electrode

Another electrode which can be used to determine the pH is

antimonya electrode . This electrode when immersed in an aqueous

solution can be disguised by oxidation and provide a response to the

H+ (Khopkar, 1990).

Eg (Potential electrode) formed of unequal voltage on the inner

surface and the outer surface of the membrane. If Esel from

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Literature Reviewantimony= 0,145 V and use buffer pH= 7, then there is no voltage

can not be read as a result of potential electrode can not be used

(Khopkar, 1990).

ESel= E°Sel= -0,059 pH

Esel=0,145= -0,059 pH

3. The Glass Electrode

Glass electrode is an electrode that is most sensitive to H+ ions and

two electrons are separated by a thin membrane , then (Khopkar,

1990):

Eg=RTnFln¿¿¿

Eg=0,0591( pH 2−pH1)

Picture II.4 Glass Electrode

Glass electrode is an electrode that is most often used because it shows a

fairly accurate pH measurements but with the range pH 2-12 glasses even

then depending on the materials used . In general, interference occurs

above pH 12 Na+ ions while under 2 formed gel thus reducing movement

or circulation between ions (Khopkar, 1990).

II.1.3 Potentiometric Titration

Emf measurements can be used to determine the endpoint. In the

acid-base titration, the pH will rise slowly to the addition of base. The very

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The increase in pH can be followed by a potentiometer, by inserting

electrodes equilibrium with H + ions and combine with kolomel electrodes.

Since the second electrode was fixed, then the increase in accordance

with the increase emf E and the first electrode is directly proportional to

the pH of the solution (Sukardjo, 2013).

II.1.3.1 Terms of potentiometric titration process

Titration process can again be followed by potential measurements

still have the following requirements (Khopkar, 1990). :

1. The reaction must involve a change or reduction of some ions in

accordance with the type of electrode.

2. Potential measurements began shortly after the addition of a

small amount of titrant in a row or continuous

3. Precision can be increased by comparing the process with a

concentration cell

II.1.3.2 Kind of Titration

Kind of titration which can be determined by potentiometric titration

(Khopkar, 1990) :

a. Titration Neutralization

Acid-base titration can be followed by the indicator electrode glass

electrode. Ionization constants must be less than 10-8 (Khopkar,

1990).

Picture II.5 Titration Curve

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c. Deposit formation or complex formation of hydrated ions from a

solution freed in general . Electrodes used is the electrode Ag , Hg

sedangkana pentitrannya is EDTA used for various metal ions

(Khopkar, 1990).

Image II.6 Titration complex formation and deposition

d. Redox Titration

Redox titration is usually used as the electrode is a platinum

electrode can be used in redox titration with oxidizing agents -

strong oxidizing agents such as KMnO4, K2Cr7O7 , Co(NO3)3 to form a

metal oxide layer that must be freed by the reduction reaction (to

liberate metals from okidasinya) is cathodic in solution aqueous

(Khopkar, 1990).

MnO Mn + O2

2Cr2O3 4Cr + 3O2

2 Co2O3 4Co + 302

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Picture II.7 Redox Titration

e. Titration in non-aqueous solvent

For example, 2,4 dinitrophenol hydrazine acting as an acid when

dissolved in pyridine. Penetration of tetrabutyl ammonium hydroxide

used in benzene (C6H6) or pure C2H5OH working electrode used is a

glass electrode, while the electrode potential in comparison to the

calomel electrode (E-sel) indirectly measured with a voltmeter

voltmeter is interesting because the work flow of the cell to be

measured potentiometer equipment (Khopkar, 1990).

Picture II.8 Potentiometer Nernst Stone Bridge

In this potentiometer W so that there is a potential regulator layout

XW and YW will show the proportion comparable to the distance between

both of them. To determine an unknown cell potential, cell tersebt will be

connected in series with gawanometri (G) which is placed between the

point and W is shifted so that it can be concluded within the XW = cell

potential unknown (Khopkar, 1990).

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Literature ReviewGalvanic cell potential depends on the activity of certain ionic

substances in solution so that the cell potential measurement cell is very

important in analytical chemistry. In many ways a cell can be arranged

that potential depends on the activity of a single kind of ionic substances

in solution. One of the cell electrodes must be such that potential depends

on the activity of the ion to be determined; This is called the indicator

electrode. The other electrode is a benchmark, such as calomel, whose

potential is known and fixed during measurement (Day &Underwood, 2002).

Excess potentiometric methods, including low cost. Voltmeter and

electrode is much cheaper than the instruments of the most modern

scientific. The models are suitable for direct potentiometric field far from

the laboratory are an inexpensive, compact, robust, and easy to use.

Potentiometric basically bersid = fat nondestructive to the sample in the

sense that the insertion of the electrode does not change the composition

of the test solution (except for a slight leakage of electrolyte from the

reference electrode). If the species indicator electrode responded by

participating in the equilibrium solution, the activity is measured when it is

present, without disturbing the equilibrium itself, thus the direct

potentiometric often very useful to define the equilibrium constant. Stable

potentials are often obtained with fairly quickly, and the voltage is

recorded as continuous monitoring and unsupervised for samples such as

communal water, industrial process streams, waste water flowing to the

pH and other ions such as fluoride, nitrate , sulfide, and cyanide (Day

&Underwood, 2002).

But one of the limitations in the accuracy of the direct

potentiometric seen in nurses equation itself. Because analyte activity

appeared in the form of logs, a change of ten times in accordance with

changes in cell voltage of only about 59 mV in the best case, where n (the

number of electrons in the electrode) is 1. But it should be recalled that

this is not'm really be a problem. Accuracy of measurement voltage is

usually not so ignored in direct potentiometric (Day &Underwood, 2002).

II.1.4 Types of Electrodes

According to Sukardjo (2013) from “Kimia Fisika” book, electrodes are

divided into:

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This electrode consists of a metal equilibrium with the metal ions

such as Zn, Cu, Cd, Na, and so on.

b. Amalgam Electrodes

Similar to the metal-metal ion electrode, but used amalgam, more

active and lower metal activity because diluted Hg.

c. Non-metal-non-gas

This electrode can be prepared by placing the substance concerned

in the tube, then on it was given a solution of the corresponding

ions. Relationship with water can be carried out with an inert metal

such as Pt.

d. Gas

Gas electrode consists of condensed gas bubbled into the solution

containing the ion equilibrium with it, as relations with the outside

usually used Pt Pt coated black.

e. Metal-insoluble salts

In this regard include:

- Electrode kolomel

- Silver-silver chloride electrodes

- Electrode lead-lead sulfate

- Electrode silver-silver bromide

These electrodes equilibrium with the residual acid ions of the salt

concerned.

f. Metal-oxide insoluble

These electrodes equilibrium denngan OH- ions in solution. Of this is

a matter of electrode Sb / Sb2O3 (s), OH.

g. Oxidation-oxidation

This electrode consists of Pt metal included in the solution formed

oxidation and reduction.

II.2 Aplikasi Industri

Potentiometric Method Application Study On Determination of

Total Organic Carbon Content of Soil

Abdul Haris Watoni and Buchari

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Literature ReviewDepartment of Chemistry, State University of Haluoleo Department of

Chemistry, Faculty of ITB

Elemental carbon in the soil are within 4 form, which form carbonate

minerals, solid elements such as charcoal, graphite and coal, humus form

as the remains of plants and animals and microorganisms that have

undergone a change, yet are relatively resistant to weathering and form

the final form the remains of plants and animals that have undergone

decomposition in the soil. In connection with the beings of the element

carbon in the soil, then the determination of the carbon content of the soil

is done based on the total organic carbon content. Some researchers have

carried out measurements of the total organic carbon content of the soil

with conventional methods, is regular titrimetric method. Titrimetric

method has a fundamental weakness especially fowl determination of the

end point of the titration. This weakness is often the case in an analysis

workmanship resulting bias measurement results obtained, in addition to

the weaknesses due to errors occurring at different stages of the process.

Based on these reasons, it is necessary to have an alternative method that

can be applied in the determination of total organic carbon content of the

soil. In this study has tried determination of total organic carbon content of

the soil by the potentiometric method using CO2 selective electrode. As a

comparison has been done also the determination of total organic carbon

content of soil with regular titrimetric method.

A calibration curve as a comparison curve for the determination of

total soil organic carbon is made of redox reaction between a mixture of

oxalic acid solution of 0.1 M and 0.1 M H2SO4 with KMnO4 0.1 M, so that the

CO2 is obtained with a concentration of 5 x 10-4 M, 5 x 10-3 M, 10-2 M, 5 x

10-2 M and 0.1 M while measuring the potential response along with doing

stirring. Next create a graph of potential (mV) against -log [CO2] as a

calibration curve. Measurement of CO2 potential response oxidation results

in total soil organic C with KMnO4 solution in acidic conditions conducted

by three (3) parameters, namely on the weight and volume of soil samples

fixed H2SO4 (parameter 1), the sample weight variable and fixed volume

H2SO4 (parameter 2 ), and the weight of the sample fixed but varies the

volume of H2SO4 (parameter 3). For the determination of the

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Literature Reviewpotentiometric method, 2 grams of dried soil sample is inserted into a

glass beaker containing 25 ml. H2SO4 0.1 M, then titrated with 0.1 M

KMnO4 in excess while stirring and measured its potential, to obtain the

greatest potential CO2 when measured by CO2 selective electrode. This

potential price subsequently incorporated into the regression equation of

the calibration curve that has been made.

The results of measurements of the optimum conditions of soil

samples with parameters 1, 2 and 3 show that for the degradation of soil

total organic carbon to CO2 is absolutely necessary KMnO4, while the

greater number of soil samples were degraded the more KMnO4 necessary,

so that the greater the concentration of CO2 produced . The amount of

H2SO4 most good for the ongoing degradation of 2 grams of soil samples

with KMnO4 was 30 mL. In this condition, the potential value of its CO2

reaches the largest value which means that the redox reaction takes place

most effectively. Retrieved also the concentration of CO2 and at the same

time the total soil organic carbon concentration-order A, B, C and D with

successive potentiometric method was 2.86 x 10-3 M, 3.72 x 10-3 M, 3.43 x

10-3 M and 6.68 x 10-4 M or 0.045%, 0.06%, 0.056% and 0.01%, while the

measurement results with titrimetric method is 0.097%, 0.147%, 0.120%

and 0.071%. The difference in these results indicate that the total soil

organic carbon determination by potentiometric method is lower than the

usual titrimetric method. It was alleged that K MnO4 added not only react

with organic compounds but also react with inorganic reducing agent

present in the soil, among other compounds of iron (II). From this vantage

point method for determining total organic carbon in the soil is more

accurate than the titrimetric method.

CO2- selective electrode can be used to determine the CO2 in solution

concentration of analyte in th area 9.09 x 10-4 M to 3.8 x 10-1 M with Nernst

factor at a temperature of 250C for 53 mV / decade and a detection limit of

4.5 x 10-4 M, while the condition of potential measurements of CO2 are best

done at pH 4.8. The presence of ions CH3COO- and H2PO4- with

concentrations of 10-2 M or more in the analyte solution can interfere with

the measurement of CO2 potential response. Potentiometric method can

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Literature Reviewbe used as an alternative method is more accurate than the titrimetric

method for the determination of total organic carbon content of the soil.

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