52235891 Group Report 1 Analytical Chemistry

8/3/2019 52235891 Group Report 1 Analytical Chemistry

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Group 2

Fransiskus Adithya Ivan Ardianto Puspita Anggreaini William Andreas

Group 2

Group Report 1

Analytical ChemistryElectrochemistry and Potentiometry


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Group Report PBL-1 Analytical Chemistry

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Table of ContentsProblem Definition .............................................................................................................................3

Background Theory ............................................................................................................................3

Electrochemistry ................................................................................................................................3

Oxidation/ Reduction Concept ................................................................................................................. 3

Types of Electrochemical Cells .................................................................................................................. 3

Effect of Concentration on Electrode Potentials The Nernst Equation ................................................. 4

NiCd Battery .............................................................................................................................................. 4

Memory Effect .......................................................................................................................................... 5

Application of NiCd Battery and compared with other types of batteries ............................................... 5

Impact in environment ............................................................................................................................. 6

Potentiometry ...................................................................................................................................6

Direct Potentiometric technique .............................................................................................................. 6

Standard Addition technique .................................................................................................................... 7

Excess standard addition and Direct Potentiometric .............................................................................. 7

Trigger Problem Answers ...................................................................................................................7

Assignment I .............................................................................................................................................. 7

Assignment II ........................................................................................................................................... 12

Assignment III .......................................................................................................................................... 14

References ....................................................................................................................................... 16

Learning Scheme (Mindmap) of Electrochemistry and Potentiometry.................................................16


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Problem Definition1. To understand the concept of batteries in correlation to the electrochemical concept.2. To understand the concept of potentiometry to determine the concentration of heavy metals,

such as copper.

Background Theory

Electrochemistry

Oxidation/ Reduction Concept

1. Oxidation Reduction reactions can be conducted in 2 ways :a. Direct contact between the oxidants and reductans.b. In a reaction in which the reactants do not come in direct contact with one another.

2. Example: Immersing a strip of copper (Cu) in a solution containing silver nitrate (AgNO 3). Here,there is an oxidation and reduction reaction happens between the copper and the solution.

Reduction (Silver Nitrate) CATHODE Oxidation (Cooper) ANODEAg

++ e

- Ag(s) Cu Cu2+ + 2e-

Oxidation and reactions has an unique characteristic of the transfer of electrons. Note that in

the 2nd type of the oxidation reduction, a salt bridge isolates the reactants but maintain

electrical contact between the CATHODE and ANODE cells.

3. The voltmeter measures the potential difference between the two metals at any instant, andthere is a tendency of the potential decrease approaching 0 V as the reaction approaches the

state of equilibrium. When zero voltage is reached, the concentrations of the 2 ions (in this case

the Ag (I) and Cu (II) will have values that satisfy the equilibrium-constant expression for the net

reduction/oxidation reaction

2 Ag+

+ Cu(s) 2Ag(s) + Cu2+

At the equilibrium condition, there is no further flow of electrons will occurs.

Types of Electrochemical Cells

Electrochemical cells are either galvanic or electrolytic, and can also classified as reversible or

irreversible. The table below describes the difference between the galvanic and electrolytic cells.

Galvanic (Voltaic) Electrolytic

Store electrical energy. Proceed spontaneusly.

Need / consume electricity. Occurs at the reverse of the galvanic cell

reactions. Cannot be conducted

spontaneusly.


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A reversible cell is a electrochemical cell that can be reversed either in galvanic or electrolytic condition,

while an irreversible cell, the cell cannot be reversed because it could cause an entirely different half-

reaction to occur at both electrodes.

Effect of Concentration on Electrode Potentials The Nernst Equation

There is a quantitative relationship between concentration and the potential difference value of the

electrodes.

Consider the reversible half reaction:

aA + bB + ... + ne- cC + dD + ...

where the capital letters represent chemical formulas for the participating species (atoms, molecules, or

ions), e-

represents electrons, and the lower case italic letters indicates the number of moles of each

species appearing in the half-reaction as it has been written. The electrode potential E for this process is

described by the equation

Where

Eo = the standard electrode potential, which is a characteristics constant for each half-reaction

R = the gas constant 8.314 J K-1

mol-1

T= temperature in kelvins

n= number of moles of electrons that appear in the half-reaction for the electrode process as it has been

written

F= the faraday = 96,485 C (coulombs)

Ln= the natural logarithm = 2.303 log

Substituting numerical values for the constants, converting to base 10 logarithms, and specifying 25oC

for the temperature give

Both equations above are named before Walther Hermann Nerst, a German physical chemist.

NiCd BatteryThe nickel-cadmium battery (commonly abbreviated NiCd or NiCad ) is a type of

rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes . the

components of NiCd battery are:

Cathode : Nickel (III) NiO(OH) Anode : Cadmium
http://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Rechargeable_battery&prev=_t&rurl=translate.google.co.id&usg=ALkJrhgHzIcxALEEbyIK-PYyAMkGHeNFpwhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Nickel_oxide_hydroxide&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhZ-rLkAudm3g3uUc8XqGZjJ4kN_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Cadmium&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjaAdPm8eFsU6VUZvYKPcXbUd_3_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Electrode&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjfpuCqAOvQMlueJXqzQS-T0sUdDAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Electrode&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjfpuCqAOvQMlueJXqzQS-T0sUdDAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Cadmium&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjaAdPm8eFsU6VUZvYKPcXbUd_3_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Nickel_oxide_hydroxide&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhZ-rLkAudm3g3uUc8XqGZjJ4kN_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Rechargeable_battery&prev=_t&rurl=translate.google.co.id&usg=ALkJrhgHzIcxALEEbyIK-PYyAMkGHeNFpw


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A separator Electrolytes : alkaline (KOH)

The reaction in electrodes when NiCd battery discharge:

(at anode)

+ (at cathode)

The reaction happen from left side to right side when discharge and rechargeable at the opposite.

Memory EffectNiCd batteries may suffer from a " memory effect " if they are discharged and recharged to the

same state of charge hundreds of times. The apparent symptom is that the battery "remembers" the

point in its charge cycle where recharging began and during subsequent use suffers a sudden drop in

voltage at that point, as if the battery had been discharged. if the device is unable to operate through

this period of decreased voltage, it will be unable to get enough energy out of the battery, and for all

practical purposes, the battery appears "dead" earlier than normal.

The mechanism of memory effect is: the active material cadmium in NiCd Battery is small

crystals which cover all the surface of NiCd cells. When memory effect happened, the crystals cover the

active materials (Ni,Cd) and cause the drop voltage.

Application of NiCd Battery and compared with other types of batteries

NiCd battery use in many thing, for example the primary cell of NiCd battery usually use in electronic

portable and toys. The main application of NiCd battery in cordless telephone and wireless, emergency

lamps, and in the plane. Because of the low resistance, the NiCd battery has a high voltage current, and

usually use in remote control, and camera, electric vehicles and standby power.

Types of Batteries

Type of Battery Information Comparison with NiCd Battery

1.Lead acid Battery Have a higher density than NiCd.Anode: Pb; Cathode: PbO2;

Electrolyte : H2SO4. The main

application in otomotive

NiCd battery is smaller andlighter than lead acid battery

2.Alcaline Battery Irreversible chemical reaction in

alkaline battery. The voltage of

NiCd battery has smaller capacity

and need high cost to produce.
http://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Memory_effect&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhOs2lGXjBMb8yEcrIjHD0y-sLsDwhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/State_of_charge&prev=_t&rurl=translate.google.co.id&usg=ALkJrhiEvPPl0Js-Apt1hpHqw5vF0h3OhAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/State_of_charge&prev=_t&rurl=translate.google.co.id&usg=ALkJrhiEvPPl0Js-Apt1hpHqw5vF0h3OhAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Memory_effect&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhOs2lGXjBMb8yEcrIjHD0y-sLsDw


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alkaline battery was drop when

charge drop. Many of them are

disposable battery. Anode: Zn;

cathode: MnO2; electrolyte: Zink

cloride

NiCd battery last longer and

keep the constant voltage when

discharge.

3.Lithium Ion Battery Rechargeable, and will broke

when discharge in minimum

voltage. Anode: lithium; cathode

and electrolyte: variation. The

main application in phonecell,

laptop, computer, and camera

NiCd battery last longer

(rechargeable)

4. Nickel Hydrida Battery (NiMH) NiMH has bigger capacity and

not toxic because the hydride

adsorb the alloy in anode. Low

cost to produce. The main

applicationin hydride vechicle

and prototype humanoid robot.

NiCd battery has low self

discharge, 20%/ month (NiCd

battery, 30%/month). NiCd not

cause voltage decreases. Low

resistance cause the high charge

flow.

Impact in environment

All of the batteries have chemical materials which cause dangerous impact in environment. The most

dangerous materials are heavy metals which carcinogenic, example: mercury and cadmium. It can cause

substantial pollution when land filled or incinerated. Because of this, many countries now operate

recycling programs to capture and reprocess old batteries. For the people, it can cause cancer, health

problem, and died.

Potentiometry

Direct Potentiometric technique

This technique requires only an indicator of potential measurement of the electron when it is dipped in

a solution containing an unknown concentration of an analyte and unknown. Indicator electrode is

always considered as a cathode and reference electrode as the anode. For the direct potentiometry

measurements, the cell potential can be expressed as a potential development by the indicator

electrode, reference electrode, and potential functions. It depends on the potential difference

measurement of electrodes in a solvent. Potential difference can be measured with pH

meters/voltmeter. An electrodes is indicator electrode which use to give the response to the solvents.
http://en.wikipedia.org/wiki/Pollutionhttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Incinerationhttp://en.wikipedia.org/wiki/Battery_recyclinghttp://en.wikipedia.org/wiki/Battery_recyclinghttp://en.wikipedia.org/wiki/Incinerationhttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Pollution


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For calculations, the sign convention for direct potentiometry is the same as the convention mentioned

in the general electrochemistry section for standard electrode potential. The indicator electrode is

always treated as the right-hand electrode and the reference electrode as the left-hand electrode.

The potential difference for the direct potentiometry follows this equation:

After a long derivation from the Nerstian form of the equation, and also considering the activity factor

versus the concentration, the final equation that can be used:

This equation effective for the cations. Meanwhile for the anions:

Standard Addition technique

This technique is commonly used in analytical instrumentation such as in atomic absorption

spectroscopy and gas chromatography to find the value of the concentration of the substance (analyte)

in a sample of unknown composition by comparison to samples of known concentration.

Excess standard addition and Direct Potentiometric

Calibration and measurement of samples done simultaneously so that the difference in ionicstrength and temperature standards and the sample is not too significant.

During the process, the electrodes remain immersed in the solution so that there is little changein junction potential solution.

Measurement of slope very close to the concentration of the sample shows this method canyield more accurate results in the range of non-linear and can be used with electrodes old or

older who was not linear range for the slope is stable.

Trigger Problem Answers

Assignment I1. According to you why a particular black box on the plane should have its own backup powersupply? What do you think are important issues to this topic?

Answer:

Backup power supply

Because simply maintaining the operation of the flight data recorder would not beenough, all of the systems and sensors that require electrical power would also have to


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remain operative. Now for the cockpit voice recorder, we only need to power the

recorder itself and the microphones in the cockpit. An independent power supply here

might not be too difficult to implement.

Because in the event of engine failure, larger aircraft are also equipped with emergencybackup power sources like the auxiliary power generator and ram air turbine to

continue operating the black boxes. In addition, we must consider to making a battery

mandatory on solid-state recorders to provide an independent power supply in the

event of a complete power failure aboard the plane.

Black boxes are sometimes never found or too badly damaged to recover some or all ofthe data from a crash. To reduce the likelihood of damage or loss, some more recent

designs are self-ejecting and use the energy of impact to separate themselves from the

aircraft. So, we must provide the recorders with a backup battery to operate the

devices for up to ten minutes if power is interrupted.

2.

Because the paper will be presented in front of the jury who come from different disciplines,you are trying to make the summary of the concept and its relation to the electrochemical

battery. What will you write?

Answer:

A Galvanic cell is an electrochemical cell that derives electrical energy from chemical

reactions taking place within the cell. It generally consists of two different metals connected

by a salt bridge, or individual half-cells separated by a porous membrane. It is sometimes

called a "Voltaic cell", after Alessandro Volta, inventor of the voltaic pile, the first electrical

battery. In common usage, the word "battery" has come to include a single Galvanic cell, but

a battery properly consists of multiple cells.
http://www.aerospaceweb.org/question/electronics/q0044c.shtmlhttp://www.aerospaceweb.org/question/electronics/q0044c.shtml


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A Galvanic cell consists of two half-cells. In its simplest form, each half-cell consists of a metal

and a solution of a salt of the metal. The salt solution contains a cation of the metal and

an anion to balance the charge on the cation. In essence the half-cell contains the metal in

two oxidation states and the chemical reaction in the half-cell is an oxidation-reduction (redox)

reaction, written symbolically in reduction direction as

Mn+

(oxidized species) + n e M (reduced species)

In a galvanic cell one metal is able to reduce the cation of the other and, conversely, the other

cation can oxidize the first metal. The two half-cells must be physically separated so that the

solutions do not mix together. A salt bridge or porous plate is used to separate the two solutions

yet keep the respective charges of the solutions from separating, which would stop the chemical

reactions.

The number of electrons transferred in both directions must be the same, so the two half-cellsare combined to give the whole-cell electrochemical reaction. For two metals A and B:

An+

+ n e A

Bm+ + m e B

m A + n Bm+ n B + m A

n+

When a metal in one half-cell is oxidized, anions must be transferred into that half-cell to

balance the electrical charge of the cation produced. The anions are released from the other

half-cell where a cation is reduced to the metallic state. Thus, the salt bridge or porous

membrane serves both to keep the solutions apart and to allow the flow of anions in the

direction opposite to the flow of electrons in the wire connecting the electrodes.

The voltage of the battery is the sum of the voltages of the two half-cells. When a device such as

an electric motor is attached to the electrodes, a current flows and redox reactions occur in

both half-cells. This will continue until the concentration of the cations that are being reduced

goes to zero.

3. From literature you read that type of batteries widely use in aircraft is the type of NiCdbatteries. What shorts of thing are associated with this battery? It is true that NiCd batteries

have memory effect?

Answer:

NiCd Battery


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The nickel-cadmium battery (commonly abbreviated NiCd or NiCad ) is a type of

rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes .

The components of NiCd battery are:

o Cathode : Nickel (III) NiO(OH)o Anode : Cadmiumo A separatoro Electrolytes : alkaline (KOH)

The reaction in electrodes when NiCd battery discharges:

(at anode)

+ (at cathode)

The reaction happen from left side to right side when discharge and rechargeable at the

opposite.

Memory Effect

NiCd batteries may suffer from a " memory effect " if they are discharged and recharged

to the same state of charge hundreds of times. The apparent symptom is that the battery

"remembers" the point in its charge cycle where recharging began and during subsequent use

suffers a sudden drop in voltage at that point, as if the battery had been discharged. if the

device is unable to operate through this period of decreased voltage, it will be unable to get

enough energy out of the battery, and for all practical purposes, the battery appears "dead"

earlier than normal.

The mechanism of memory effect is: the active material cadmium in NiCd Battery is

small crystals which cover all the surface of NiCd cells. When memory effect happened, the

crystals cover the active materials (Ni,Cd) and cause the drop voltage.

4. How do you think the development and application of NiCd battery compared to other battery?Do you know about zapping technique in improving battery performance? What do you think

about environmental impact of disposable and rechargeable batteries?

Answer:

NiCd battery use in many thing, for example the primary cell of NiCd battery usually use in

electronic portable and toys. The main application of NiCd battery in cordless telephone and

wireless, emergency lamps, and in the plane. Because of the low resistance, the NiCd battery
http://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Rechargeable_battery&prev=_t&rurl=translate.google.co.id&usg=ALkJrhgHzIcxALEEbyIK-PYyAMkGHeNFpwhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Nickel_oxide_hydroxide&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhZ-rLkAudm3g3uUc8XqGZjJ4kN_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Cadmium&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjaAdPm8eFsU6VUZvYKPcXbUd_3_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Electrode&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjfpuCqAOvQMlueJXqzQS-T0sUdDAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Memory_effect&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhOs2lGXjBMb8yEcrIjHD0y-sLsDwhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/State_of_charge&prev=_t&rurl=translate.google.co.id&usg=ALkJrhiEvPPl0Js-Apt1hpHqw5vF0h3OhAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/State_of_charge&prev=_t&rurl=translate.google.co.id&usg=ALkJrhiEvPPl0Js-Apt1hpHqw5vF0h3OhAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Memory_effect&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhOs2lGXjBMb8yEcrIjHD0y-sLsDwhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Electrode&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjfpuCqAOvQMlueJXqzQS-T0sUdDAhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Cadmium&prev=_t&rurl=translate.google.co.id&usg=ALkJrhjaAdPm8eFsU6VUZvYKPcXbUd_3_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Nickel_oxide_hydroxide&prev=_t&rurl=translate.google.co.id&usg=ALkJrhhZ-rLkAudm3g3uUc8XqGZjJ4kN_Qhttp://translate.googleusercontent.com/translate_c?hl=id&ie=UTF-8&sl=en&tl=id&u=http://en.wikipedia.org/wiki/Rechargeable_battery&prev=_t&rurl=translate.google.co.id&usg=ALkJrhgHzIcxALEEbyIK-PYyAMkGHeNFpw


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has a high voltage current, and usually use in remote control, and camera, electric vehicles and

standby power.

Types of Batteries

Type of Battery Information Comparison with NiCd

Battery

1.Lead acid Battery Have a higher density than NiCd.

Anode: Pb; Cathode: PbO2;

Electrolyte : H2SO4. The main

application in automotive

NiCd battery is smaller

and lighter than lead

acid battery

2.Alcaline Battery Irreversible chemical reaction in

alkaline battery. The voltage of

alkaline battery was drop when

charge drop. Many of them are

disposable battery. Anode: Zn;

cathode: MnO2; electrolyte: Zink

cloride

NiCd battery has smaller

capacity and need high

cost to produce. NiCd

battery last longer and

keep the constant

voltage when discharge.

3.Lithium Ion Battery Rechargeable, and will broke

when discharge in minimum

voltage. Anode: lithium; cathode

and electrolyte: variation. The

main application in phonecell,

laptop, computer, and camera

NiCd battery last longer

(rechargeable)

4. Nickel Hydrida Battery (NiMH) NiMH has bigger capacity and

not toxic because the hydride

adsorb the alloy in anode. Low

cost to produce. The main

applicationin hydride vechicle

and prototype humanoid robot.

NiCd battery has low

self discharge, 20%/

month (NiCd battery,

30%/month). NiCd not

cause voltage

decreases. Low

resistance cause the

high charge flow.

Impact in environment

All of the batteries have chemical materials which cause dangerous impact in environment. The

most dangerous materials are heavy metals which carcinogenic, example: mercury and

cadmium. It can cause substantial pollution when land filled or incinerated. Because of this,

many countries now operate recycling programs to capture and reprocess old batteries. For the

people, it can cause cancer, health problem, and died.
http://en.wikipedia.org/wiki/Pollutionhttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Incinerationhttp://en.wikipedia.org/wiki/Battery_recyclinghttp://en.wikipedia.org/wiki/Battery_recyclinghttp://en.wikipedia.org/wiki/Incinerationhttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Pollution


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Disposable Battery Rechargeable battery

Primer battery, ex: leclanche cell (1,5 V) Anode: Zn ; cathode: carbon tube ;

electrolyte: MnO2 and NH4Cl

Reaction :Zn(s)+2MnO2(s)+2NH4Cl(aq)ZnCl2+Mn2O3(s)

+2NH3(aq)+H2O

Used in telegraf, alarm, and low voltageinstruments

Secunder battery, ex: superiron battery.

Cathode: Fe(VII), K2FeO4;anode: zink, electrolide:ammonium chloride and zink

chloride.

50% capacity higher thanalkaline battery.

The new type battery developin 2004

Assignment II

1. What reactions occur on each electrode in this electrochemical cell if the total reaction iswritten:

() ()Answer:

In anode, the oxidation process occurs. The half reaction is: ()

In cathode, the reduction process occurs. The half reaction is: ()

2. How to make electrolyte solution in order to obtain batteries with a voltage of 1.5 V at atemperature of 25

o

C?

Answer:

Using Nerst Equation:

Standard Electrode Potential of:

Mn (Reduction): +1,23 V Zn (Oxidation : +0,763 V

Total Electrode Potential: +1,993 V

Substituting the Potential and the Potential desired to the Nerst Equation:


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[] Corresponding to the unknown values of the concentration of [Mn

3+],[Mn

4+] or [Zn

2+], the

answer is given in ratio of both concentrations.

3. How do you explain the parameters of the battery capacity in amp-hour and battery voltage inV? How to estimate the life of batteries?

Answer:

Battery voltage is related to the potential difference between the two half reactions occured at

the anode (oxidation reaction) and the cathode (reduction reaction). For example, the 1,5 Volt

potential difference in common AA and AAA sized battery are derived from the half reaction of

their cells, with the respective to their temperature and concentration (following the Nerst

equation).

The lifetime of batteries can be determined by the Peukerts Law:

Where :

Qp : capacity when discharged at the rate of 1 amp. I : the current drawn from the battery. t : time the battery can sustain k : constant with a value about 1,3.

4. Why do you use graphite or carbon bar as electron flow collector on the cathode side nit onlythe MnO2

Answer:

Carbon takes no part in the electrochemical reaction, but it collects the electrical current and

reduce the resistance of the manganese dioxide mix.


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Assignment III

1. How do you determine the possibility of this river was polluted by copper from the industrialwaste? Do you know what industries that have copper in their waste?

Answer:

Determination of copper content in the waste industry can be determined by thepotential difference through which components such as reference electrode, indicator

electrode, and salt bridges. These components can be interconnected to produce a potential

difference. From this it can be determined the presence of copper content in the wastewater

plant.

Industry-industry wastes containing copper, among others. wire mills, metal coatings, pipes and

others.

2. In the laboratory you have a pH meter/ volt meter, a standard saturated calomel electrode, andan indicator electrode for copper analysis. Because the committee will assess the project

proposal, can you explain in the proposal the method of analysis to determine the content of

copper ion in samples taken from the stream using existing equipment? The information is clearenough in terms of both instrumentation and theoretical basic principle of this analytical

method.

Answer:

This is the technical set-up for the potentiometry method. The voltmeter is being set in series

with the indicator electrode (in this case is the copper metal, because it is a copper

concentration analysis) and the reference electrode (the standard saturated calomel electrode).

Meanwhile the analyzed solution is poured at the glass beaker where both the indicator and

reference cathode is being set. After the setup has been completed, we measure the voltagedifference displayed at the voltmeter.

The concentration of the analyzed

solution can be determined by using the

Nerst equation or the derivatives of the

equation.

3. By using the directpotentiometric technique, you obtaindata such as in figure. How do you

determine the concentration of copper in the sample?

Answer:

From the table, we can collect some data such as:

Slope: 0.0302V


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ECu-ISE: 0.2524V

We also take the standard potential data of the reduction reaction of copper:

We input the data into the nerst equation:

[]

4. How do you explain the determination of copper concentration in the sample solution withstandard addition technique? How do you explain the difference in direct potentiometric

determination technique and standard addition technique?

Answer:

Step in addition standard technique:

From the sample, determine the aliquot identical, Vx. adding a number of specific volume

variation, Vs. its dilute each solution to a particular volume, Vt. Then calculate concentration on

sample, Cu, with equation:

Cu=

Cu= concentration in unknown sample

Cs= concentration in standard sample

Vs= standard volume

Vu= Sample volume

E1= electro potential in pure solvent

E2= electrode potential in addition

m= electrode slope

Direct Potentiometric technique

This technique requires only an indicator of potential measurement of the electron when it is dipped in

a solution containing an unknown concentration of an analyte and unknown. Indicator electrode isalways considered as a cathode and reference electrode as the anode. For the direct potentiometric

measurements, the cell potential can be expressed as a potential development by the indicator

electrode, reference electrode, and potential functions. It depends on the potential difference

measurement of electrodes in a solvent. Potential difference can be measured with pH

meters/voltmeter. An electrodes is indicator electrode which use to give the response to the solvents.

Standard Addition technique


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This technique is commonly used in analytical instrumentation such as in atomic absorption

spectroscopy and gas chromatography to find the value of the concentration of the substance (analyte)

in a sample of unknown composition by comparison to samples of known concentration.

Excess standard addition and Direct Potentiometric

Calibration and measurement of samples done simultaneously so that the difference in ionicstrength and temperature standards and the sample is not too significant.

During the process, the electrodes remain immersed in the solution so that there is little changein junction potential solution.

Measurement of slope very close to the concentration of the sample shows this method canyield more accurate results in the range of non-linear and can be used with electrodes old or

older who was not linear range for the slope is stable.

References1. Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch, Fundamentals of

Analytical Chemistry 8th

Edition. Saunders College Publishing, New York,2002.

2. http://en.wikipedia.org/wiki/Battery3. http://en.wikipedia.org/wiki/potentiometry4. http://en.wikipedia.org/wiki/Ni-Cd

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52235891 Group Report 1 Analytical Chemistry