Mathematics Education - WordPress.com · 2011-05-31 · Electrodes of metal, graphite and semiconductor material are widely used. Choice of suitable electrode depends on chemical

Redox reaction, Electrolysis and Electrochemistry

group 8

1. Rini Kurniasih K1310069

2. Susi Cahyanti K1310076

3. Wahyu Nugroho K1310082

Mathematics Education

Training Teacher and Education Faculty

SEBELAS MARET UNIVERSITY (UNS)

2011

2

CONTENTS

I. TITLE .............................................................. 3

II. OBJECTIVES .............................................................. 3

III. BASIC THEORY ............................................................... 3

III.1 REDOX REACTION ............................................................... 3

III.2 ELECTROLYSIS ............................................................... 5

III.3 ELECTROCHEMISTRY ............................................................... 5

IV. EQUIPMENTS AND MATERIALS ......................................................... 8

IV.1 REDOX REACTION ............................................................... 8

IV.2 ELECTROLYSIS ............................................................... 9

IV.3 ELECTROCHEMISTRY ............................................................ 10

V. PROCEDURE ............................................................. 12

V.1 REDOX REACTION ............................................................. 12

V.2 ELECTROLYSIS ............................................................. 12

V.3 ELECTROCHEMISTRY ............................................................. 12

VI. OBSERVATION DATA ............................................................. 13

VI.1 REDOX REACTION ............................................................. 13

VI.2 ELECTROLYSIS ............................................................. 13

VI.3 ELECTROCHEMISTRY ........................................................... 13

VII. DATA ANALYZE ............................................................. 14

VII.1 REDOX REACTION ............................................................. 14

VII.2 ELECTROLYSIS ............................................................. 16

VII.3 ELECTROCHEMISTRY ........................................................... 19

VIII. CONCLUSION ............................................................. 21

IX. BIBLIOGRAPHY ............................................................. 22

3

PAPER OF BASIC CHEMISTRY 2 EXPERIMENT

I. TITLE

Redox Reaction, Electrolysis and Electrochemistry

II. OBJECTIVES

1. Knowing the redox reaction

2. Studying about chemistry reaction by elecrtric current

3. Knowing the oxidation reaction and reduction reaction zinc

metal with cuprum in solution and measure cell potential

III. BASIC THEORY

III.1 REDOX REACTIO N

Redox (shorthand for REDuction-OXidation) reactions describe all

chemical reactions in which atoms have their oxidation number (oxidation

state) changed. This can be either a simple redox process, such as the

oxidation of carbon to yield carbon dioxide (CO2) or the reduction of

carbon by hydrogen to yield methane (CH4), or a complex process such as

the oxidation of sugar (C6H12O6) in the human body through a series of

complex electron transfer processes.

The term comes from the two concepts of reduction and oxidation.

It can be explained in simple terms:

Oxidation is the loss of electrons or an increase in oxidation state

by a molecule, atom, or ion.

Reduction is the gain of electrons or a decrease in oxidation state

by a molecule, atom, or ion.

Though sufficient for many purposes, these descriptions are not

precisely correct. Oxidation and reduction properly refer to a change in

oxidation number — the actual transfer of electrons may never occur.

4

Thus, oxidation is better defined as an increase in oxidation number, and

reduction as a decrease in oxidation number. In practice, the transfer of

electrons will always cause a change in oxidation number, but there are

many reactions that are classed as "redox" even though no electron transfer

occurs (such as those involving covalent bonds).

Non-redox reactions, which do not involve changes in formal

charge, are known as metathesis reactions.

Reduction potential is used to calculate the standard electrode potential

(Eocell).

This is the equation most commonly seen in textbooks:

where:

Eocell is the standard electrode potential (in volts).

Eored is standard reduction potential of the reducing agent.

Eooxi is negative of the standard reduction potential of the

oxidizing agent.

though the following equation is generally more useful as one is usually

only given reduction potentials, not oxidation potentials :

or equivalently:

where:

Eocell is the standard electrode potential (in volts).

Eocathode is standard reduction potential of the reducing agent.

Eoanode is the standard reduction potential of the oxidizing agent.

5

III.2 ELECTROLYSIS

Electrolysis is the passage of a direct electric current through an

ionic substance that is either molten or dissolved in a suitable solvent,

resulting in chemical reactions at the electrodes and separation of

materials.

The main components required to achieve electrolysis are :

An electrolyte : a substance containing free ions which are the

carriers of electric current in the electrolyte. If the ions are not

mobile, as in a solid salt then electrolysis cannot occur.

A direct current (DC) supply : provides the energy necessary to

create or discharge the ions in the electrolyte. Electric current is

carried by electrons in the external circuit.

Two electrodes : an electrical conductor which provides the

physical interface between the electrical circuit providing the

energy and the electrolyte

Electrodes of metal, graphite and semiconductor material are

widely used. Choice of suitable electrode depends on chemical reactivity

between the electrode and electrolyte and the cost of manufacture.

III.3 ELECTROCHEMISTRY

Electrochemistry is a branch of chemistry that studies chemical

reactions which take place in a solution at the interface of an electron

conductor (a metal or a semiconductor) and an ionic conductor (the

electrolyte), and which involve electron transfer between the electrode and

the electrolyte or species in solution.

6

If a chemical reaction is driven by an external applied voltage, as in

electrolysis, or if a voltage is created by a chemical reaction as in a battery,

it is an electrochemical reaction. In contrast, chemical reactions where

electrons are transferred between molecules are called oxidation/reduction

(redox) reactions. In general, electrochemistry deals with situations where

oxidation and reduction reactions are separated in space or time, connected

by an external electric circuit to understand each process.

An electrochemical cell is a device that produces an electric current

from energy released by a spontaneous redox reaction. Electrochemical

cells have two conductive electrodes (the anode and the cathode). The

anode is defined as the electrode where oxidation occurs and the cathode is

the electrode where the reduction takes place. Electrodes can be made

from any sufficiently conductive materials, such as metals,

semiconductors, graphite, and even conductive polymers. In between these

electrodes is the electrolyte, which contains ions that can freely move.

The Galvanic cell uses two different metal electrodes, each in an

electrolyte where the positively charged ions are the oxidized form of the

electrode metal. One electrode will undergo oxidation (the anode) and the

other will undergo reduction (the cathode). The metal of the anode will

oxidize, going from an oxidation state of 0 (in the solid form) to a positive

oxidation state and become an ion. At the cathode, the metal ion in

solution will accept one or more electrons from the cathode and the ion's

oxidation state is reduced to 0. This forms a solid metal that

electrodeposits on the cathode. The two electrodes must be electrically

connected to each other, allowing for a flow of electrons that leave the

metal of the anode and flow through this connection to the ions at the

surface of the cathode. This flow of electrons is an electrical current that

can be used to do work, such as turn a motor or power a light.

A Galvanic cell whose electrodes are zinc and copper submerged

in zinc sulfate and copper sulfate, respectively, is known as a Daniell cell.

Half reactions for a Daniell cell are these:

7

Zinc electrode (anode): Zn(s)→ Zn2+

(aq) + 2 e-

Copper electrode (cathode): Cu 2+

(aq)+ 2 e-→ Cu(s)

A modern cell stand for electrochemical research. The electrodes

attach to high-quality metallic wires, and the stand is attached to a

potentiostat/galvanostat (not pictured). A shot glass-shaped container is

aerated with a noble gas and sealed with the Teflon block.

In this example, the anode is zinc metal which oxidizes (loses

electrons) to form zinc ions in solution, and copper ions accept electrons

from the copper metal electrode and the ions deposit at the copper cathode

as an electrodeposit. This cell forms a simple battery as it will

spontaneously generate a flow of electrical current from the anode to the

cathode through the external connection. This reaction can be driven in

reverse by applying a voltage, resulting in the deposition of zinc metal at

the anode and formation of copper ions at the cathode.

To provide a complete electric circuit, there must also be an ionic

conduction path between the anode and cathode electrolytes in addition to

the electron conduction path. The simplest ionic conduction path is to

provide a liquid junction. To avoid mixing between the two electrolytes,

the liquid junction can be provided through a porous plug that allows ion

flow while reducing electrolyte mixing. To further minimize mixing of the

electrolytes, a salt bridge can be used which consists of an electrolyte

saturated gel in an inverted U-tube. As the negatively charged electrons

flow in one direction around this circuit, the positively charged metal ions

flow in the opposite direction in the electrolyte.

A voltmeter is capable of measuring the change of electrical

potential between the anode and the cathode. Electrochemical cell voltage

is also referred to as electromotive force or emf.

A cell diagram can be used to trace the path of the electrons in the

electrochemical cell. For example, here is a cell diagram of a Daniell cell:

Zn(s) | Zn2+

(1M) || Cu2+

(1M) | Cu(s)

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First, the reduced form of the metal to be oxidized at the anode (Zn) is

written. This is separated from its oxidized form by a vertical line, which

represents the limit between the phases (oxidation changes). The double

vertical lines represent the saline bridge on the cell. Finally, the oxidized

form of the metal to be reduced at the cathode, is written, separated from

its reduced form by the vertical line. The electrolyte concentration is given

as it is an important variable in determining the cell potential.

IV. EQUIPMENTS AND MATERIALS

IV.1 Redox Reaction

No. Name Picture Quantity

1. Measurement glass

1

2. Pippete

2

3. Reaction tube rack

1

4. Reaction tube

6

9

No. Name Quantity

1. Solution CuSO4 0.5M 4 ml

2. Solution ZnSO4 0.5M 4 ml

3. Solution FeCl3 4 ml

4. Metal Cu 2 piece

5. Metal Zn 2 piece

6. Metal Fe 2 piece

IV.2 Electrolysis


1. Funnel

1

2. Power supply

1

3. Carbon electrode

2

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4. Pippete

2

5. Measuring glass

1

6. U pipe

1

No. Name Quantity

1. Solution KI 0.5 M sufficient

2. Solution NaCl 0.5 M sufficient

3. Solution of PP 2 drop

4. Solution of amylum 2 drop

IV.3 Electrochemistry


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1. Funnel

1

2. Beaker glass

2

3. Multimeter

1

4. Pippete

2

5. Salt bridge

1

No. Name Quantity

1. Solution ZnSO4 0.5 M sufficient

2. SolutionCuSO4 0.5 M sufficient

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3. Salt solution sufficient

4. Metal Zn 1 piece

5. Metal Cu 1 piece

V. PROCEDURE

V.1 Redox Reaction

1. Enter 2 ml CuSO4 solution into the reaction tube add Zn metal.

Let it for several minutes and note what happen? By same way

done to Fe metal.

2. Enter 2 ml ZnSO4 solution into the reaction tube, then add Cu

metal. Let it for several minutes and note what happen by same

way, done to Fe metal.

3. Repeat by some way to FeCl3 solution with Cu and Zn metal.

V.2 Electrolysis KI and NaCl solution

1. Enter KI solution 0.5 M into U tube until glue form top and U

tube.

2. Connect electrodes with source of electric current during less

more 5 minutes.

3. Note the change at anode.

4. Note the change occur at catode with use pipette drop, add 2 drop

indicator PP solution at catode space, observe which occur.

5. By use pipette drop, add any drop amylum solution into anode

space, observe which occur.

6. Done step 1 to 5 with use NaCl 0.5 M solution.

V.3 Electrochemistry Cell

1. Making a half cell . Enter 100 ml ZnSO4 0.5 M

solution into chemistry glass 250 ml. Place a stick of zinc scuff

into the glass.

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2. Making a half cell . Enter 100 ml CuSO4 0.5 M

solution into the chemistry glass 250 ml. Plece a stick of cuprum

scuff into the glass.

3. Connect zinc scuff with negative pole of multimeter and connect

cuprum scuff with positive pole of voltmeter.

4. Connect both cell with salt bridge. Read voltmeter then note the

result.

VI. OBSERVATION DATA

VI.1 Redox Reaction

1. CuSO4+Zn there are bubble

2. CuSO4+Fe

3. ZnSO4+Cu

4. ZnSO4+Fe

5. FeCl3+Zn there are bubble and become rusty

6. FeCl3+Cu

VI.2 Electrolysis

1. KI 0.5 M

a. Change on anode (+) : yellow-brown

b. After add amylum to anode :black

c. Change on cathode (-) : bubbles

d. After add PP to cathode : purple

2. NaCl 0.5 M

a. Change on anode (+) : light yellow

b. After add amylum to anode : light yellow

c. Change on cathode (-) : bubbles

d. After add PP to cathode : purple

VI.3 Electrochemistry

toward = 0.6 volt

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VII. DATA ANALYZE

VII.1 Redox Reaction

1. Cu+ZnSO4 solution

cathode : Eored= -0.76 volt

anode : Eooxi= -0.34 volt

Eocell= -1.1 volt

Eocell is negative, therefore reaction can not happen and reactivity

Zn>Cu

2. Cu+FeCl3 solution


anode : Eooxi= -0.34 volt

Eocell= -0.412 volt


Fe>Cu

3. Fe+CuSO4 solution

cathode : Eored= 0.34 volt

anode : Eooxi= 0.44 volt

Eocell= 0.78 volt

Eocell is positive, where Cu is oxidator (doing reduction) and Fe is

redactor (doing oxidation) and the reactivity Fe>Cu so the reaction is

spontan.

4. Fe+ZnSO4 solution


anode : Eooxi= +0.44 volt

Eocell= -0.32 volt

15


Zn>Fe.

5. Zn+ CuSO4 solution



Eocell= 1.1 volt


redactor (doing oxidation) and the reactivity Zn>Cu so the reaction is

spontan.

6. Zn+ FeCl3 solution



Eocell= 0.6888 volt


redactor (doing oxidation) and the reactivity Zn>Fe so the reaction is

spontan.

Based on the experiment of redox reaction, the reaction can be occur only

CuSO4 solution add Zn metal and FeCl3 solution add Zn metal.

In the experiment we get the difference which is gotten by calculation.

From experiment Zn added in CuSO4 solution there is changes Zn become

brown and there are stratified or powder also there are bubbles. It is match

with theory hence occur reaction. While for Fe entered in CuSO4 there are

no changes. It is indicated that not occur reaction. Through the experiment,

metal Cu and Fe not react in the ZnSO4 caused not occurring changes. It is

same with metal Cu in the FeCl3 solution. In the ordered volta metals “ Li-

K-Ba-Ca-Na-Mg-Al-Zn-Fe-Ni-Sn-Pb-H-Cu-Hg-Ag-Pt-Au ” only can

reduct other metal which exist in the right side and can not reduct metal in

the left side. Metal which has law reduction potential will have reactivity.

According to volta cell set Zn-Fe-Cu.

The differences from calculating or theory with the experiment caused by:

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1. Practicant do not have much time in observing reaction, hence reaction

which must occur can not be observed. Practicant can not see bubbles

or color changes.

2. Inaccurate when metal Fe, Cu, Zn started to react.

3. The instrument not clean.

4. Metal Fe, Zn, and Cu firstly can not be sandpaper it influence the

reaction.

Reaction happen spontaneously if potential cell (Eocell) which resulted

from the reaction between metal with a solution have positive value.

Potential cell is the difference between cathode potential with anode

potential. At redox reaction in anode happen oxidation reaction and at

cathode happen reduction reaction. Reactivity metals based on calculation

in CuSO4 solution Zn>Fe, in ZnSO4 solution Fe>Cu and in FeCl3 solution

Zn>Cu.

VI.2 Electrolysis

Reaction :

cathode :

anode :

17

In KI solution we get ion K+ and I

- and water molecule, possibility

reaction which occur in the left side is reduction K+ ion or reduction of

water molecule.

Electrolyte solution can conduct electric current. Conduction

electric through solution accompanied a reaction which is called

electrolysis. Electrolysis is expansion process of electrolyte in the

solution form or break by electric current direct. These reaction can take

place because the influence of electric current. So, at electrolysis occur

changes from electric energy become chemistry energy. If the electric

flow through ion compound melt, so the ion compound will be

expansion cation reduction in cathode white anion oxidation in anode.

If which flowed by electric is electrolyte solution, so reaction which

occur not cation and anion, may be water or the electrode.

Reaction at cathode:

Eo= -2.92 volt

E

o= -0.83 volt

Because the reduction potential of water is higher so water able to be

reducted hence in cathode form H2 gasses.

Reaction in anode oxidation:

Eo= -0.54 volt

E

o= -0.83 volt

Because potential I- higher than potential of water oxidation, so at

anode form iodine which in this experiment have yellow-brown, so

oxidation ion I- will be able to occur. So, at electrolysis KI solution

occur reaction with the result H2 gases, OH-, KI. Reaction

is oxidation reaction, we can conclude that in the right side

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is anode because at anode occur oxidation reaction. While at reaction of

is reduction reaction and can be

conclude at this part look cathode.

Electrolysis KI reaction with C completely:

anode :

cathode :

When flowed by electric current KI solution occur at anode has orange

or yellow color rather brown which firstly has clear rather yellow.

Based on the experiment result which gotten at anode space which

added with amylum solution that occur changes there are change color

become brown. While at cathode space which added by PP solution the

color change from pure to purple and there exist bubbles. This show

that the solution has base properties. The changes at anode if mix with

iodine. At anode appear bubbles gass that is H2 gases.

Electrolysis NaCl 0.5 M solution

Reaction :

anode :

cathode :

Reaction which occur is below

E

o= -0.83 volt

19

Eo= -2.71 volt

At electrolysis of NaCl solution with electrode grafit appear much

bubble in the cathode (-), while in the anode (+) the solution change the

color. In the cathode there exist bubbles gases caused at this part occur

reduction H2O reaction. Like which occur at the experiment at anode

space which given amylum occur changes become much bubbles gases

of Cl2 and cathode space which added PP appear bubbles H2 gases just

little, not occur change color. From theory we know that in anode from

chlorine gases and cathode result hydrogen gases. Ion OH- which occur

react with ion Na+ hence result NaOH which can be crystaled because

the potential reduction of water is higher than Na. Therefore, water

more able to reduct hence in cathode form H2 gases. At this experiment

not show that the solution have base properties. The difference between

theory and experiment caused by less accurate doing experiment,

inaccurate when drop amylum ad PP, the instrument not clean and soon.

VI.3 Electrochemistry

If an electrolyte solution and metal which act as electrode

connected with salt bridge, so will have voltage. Voltage (different

putential) Eocell can be calculated by formula .

20

Based on the constanta, the magnitude of standart reduction

potential (Eocell)

Eo= +0.34 volt

Eo= -0.76 volt

The reaction



Eocell= 1.1 volt

Eo Cu bigger than E

o Zn, hence Cu faced reduction and Zn

oxidation. At anode occur oxidation reaction that is and

cathode occur reduction reaction . Change number (+)

which formed in anode equivalent with negative ion which formed in

cathode. Negative ions flow from salt bridge to anode, because formed

positive ion. Because negative charge formed in cathode, so positive ion

flow from salt bridge toward electrode (cathode). Salt bridge function to

arrange the equilibrium of ions solution. Metal which faced reduction is

metal which faced oxidation is metal which has Eo cell smaller or which

more difficult to reduct.

In ordered volta properties more left, the Eo reduction value smaller

means more difficult for metal to reduct (more able to oxidated) and more

right the Eo value bigger means more able to reduct. From the

electrochemistry experiment making a half cell by

entering 100 ml ZnSO4 0.5 M into beaker glass also made a half cell

entered 100 ml CuSO4 0.5 M into beaker glass and

connected both beaker glass with salt bridge. Positive pole at voltmeter

dipped in CuSO4 solution and negative pole at ZnSO4 and Eo cell at the

experiment we obtain 0.6 volt. It is different with the theory, the caused by

inaccurate to read voltmeter, instrument not clean and soon.

21

VIII. CONCLUSION

1. Redox is the term used to label reactions in which the acceptance of an

electron (reduction) by a material is matched with the donation of an

electron (oxidation). Redox reaction happen because there is difference

of potential of each element can happen if Eocell positive (E

ocell>0).

2. Order of reactivity in the experiment Zn>Fe>Cu.

3. Electrochemistry is the study of solutions of electrolytes and of

phenomena occurring at electrodes immersed in these solutions.

4. Cell potential can be calculate with formula

Magnitude of cell tension from electrochemistry

Zn(s) | Zn2+

|| Cu2+

| Cu(s)

theory : 1.1 volt

experiment : 0.6 volt

5. Electrolysis is chemical reaction when lectricity is passed through an

liquid solution of an ion or an electrolyte.

Electrolysis KI

anode :

cathode :

Electrolysis NaCl

anode :

cathode :

22

IX. BIBLIOGRAPHY

Anshory, irfan.2000.Kimia.Jakarta:Erlangga

Brady,james.1994.Kimia Universitas.Jakarta:Erlangga

Cliff.D.A et al.Chemistry Astructural View Laboratory Manual Edisi3.

G.Wulfsberg.2000.Inorganic Chemistry.University Science

Book,Sausolito,CA.

Keenan,klemfelter/.1986.Kimia Universitas.Jakarta:Erlangga

Kuswati,tine maria.2005.Sains Kimia.Jakarta:Bumi Aksara

http://wikipedia.com(access May16th

2011)

http://google.com(access May16th

2011)

Surakarta, May 17th

2011

Writer

http://wikipedia.com(access/

http://google.com(access/

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Mathematics Education - WordPress.com · 2011-05-31 · Electrodes of metal, graphite and semiconductor material are widely used. Choice of suitable electrode depends on chemical