oxidation and reduction.pdf

8/10/2019 Oxidation and Reduction.pdf

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OXIDATION AND REDUCTION

1. Reactions Oxidation and Reduction Reactions

Along with the development of science and technology, the concept of redox

reactions are also experiencing growth. At first the concept of redox reactions

based on the involvement of oxygen. Oxygen binding reaction called oxidation

reaction and reaction that releases

called oxygen reduction reaction. In the next development was found that the redox

reaction does not always involve oxygen. Experts reviewing the handover of

electrons. The oxidation reaction releases electrons while receiving electron

reduction reaction. In recent developments, the redox reaction is based on the

change in oxidation number.

Chemical changes or chemical reactions of many kinds, and one of them is the

oxidation and reduction reactions. The terms oxidation and reduction applied to

chemical change or chemical reaction of a substance (elements and compounds)

involving oxygen. Oxidation is the oxygen binding event by a substance; whereas

the release of oxygen reduction is an event of a substance. Oxideis a compound

result of merging the elements and oxygen. The oxidation reaction is accompanied

by the release of heat energy called the combustion reaction.


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Oxidation is the oxygen binding event by a substance.

Examples of oxidation reactions (oxygen binding):

(A) 2 Ca + O2 2 CaO

calcium calcium oxide

(B) 4 Fe + 3 O2 2 Fe2O3

ferrous iron (III) oxide

(C) 2 C2H5OH + 6 O2 6 H2O + 4 CO2

alcohol-water carbon dioxide

Reduction is the event release of oxygen from a substance.

Examples of reduction reaction (release of oxygen):

(A) 2 Fe2O3 + 3 C 4 Fe + 3 CO 2

iron (III) oxide iron


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(B) Cu2O + Cu + H 2 2 H2O

copper (I) oxide copper

2. The concept of redox reactions based on the incorporation and release

electron

Some oxidation reduction reaction does not involve oxygen, so the concept of

oxidation reduction needs to be expanded. For example, the reaction of Na + Cl?

To explain the concept of oxidation reduction can be observed from the handover

of the electron.

In this concept defined oxidation reduction:

Oxidation and reduction in terms of oxygen transfer

In terms of oxygen transfer, Oxidation is gain of oxygen Reduction is loss ofoxygen.

For example, in the extraction of iron from iron ore:

Because redand oxidasi uksi occur at the same time, the above reaction is called

redoxreactions.

Oxidising and reducing agents

Oxidizer or oxidizing agent is a substance that oxidizes another substance. In the

above example, iron (III) oxide is an oxidizer.

Reductant or reducing agent is a substance that reduces another substance. From

the above reaction, the carbon monoxide is the reducing agent.

So it can be concluded:


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oxidizer is giving oxygen to other substances,

Reducing agents remove oxygen from another substance

Oxidation and reduction in terms of hydrogen transfer

Definitions of oxidation and reduction in terms of hydrogen transfer has been long

and is now not much used.

Oxidation is loss of hydrogen, reduction is gain of hydrogen.

Note that what happens is the opposite of the oxygen definitions.

For example, ethanol can be oxidized to ethanal:

To move or remove hydrogen from ethanol required oxidizing agent (oxidant).

Commonly used oxidising agent is potassium dichromate (VI) solution acidified

with dilute sulfuric acid.

Ethanal can also be reduced to ethanol again by adding hydrogen. Reducing agents

which can be used for the reduction reaction is sodium tetrahydridoborate, NaBH4.

Simply put, the reaction can be described as follows:

Oxidizing agent (oxidant) and reducing agent (reductant)

Oxidizing agent (oxidant) to give oxygen to another substance, or removehydrogen from other substances.

The reducing agent (reductant) remove oxygen from another substance, or

give hydrogen to other substances.

Oxidation and reduction in terms of electron transfer

Oxidation is loss of electrons, and reduction is gain of electrons.


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This definition is very important to remember. There is an easy way to help you

remember this definition. In the case of electron transfer:

A simple example

Redox reactions in terms of electron transfer:

Copper (II) oxide and magnesium oxide are both ionic. Being in the form of non-

metal ions. If this reaction is rewritten as an ionic equation, it turns oxide ions are

spectator ions (ions audience).

If you look at the equation above, magnesium is reducing the copper (II) by giving

electrons to neutralize the charge of copper (II).

It can be said: magnesium is a reducing agent (reductant).

In contrast, the copper ions (II) electron transfer from magnesium to produce

magnesium ions. Thus, copper ions (II) acts as the oxidizing agent (oxidant).

It is rather confusing to study the oxidation and reduction in terms of electron

transfer, and learn the definition of oxidising and reducing agents in terms of

electron transfer.

Can be summarized as follows, oxidiser what role in electron transfer:

Oxidizing agent oxidizes another substance.

Oxidation is loss of electrons (OIL RIG).

That means an oxidising agent takes electrons from another substance.

So an oxidising agent must gain electrons

Or it can be summed up as follows:

An oxidizing agent oxidizes another substance.

That means oxidizing agents should be reduced.

Reduction is gain of electrons (OIL RIG).

So an oxidising agent must gain electrons.


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Oxidation and reduction in terms of oxygen transfer

In terms of oxygen transfer, Oxidation is gain of oxygen Reduction is loss of

oxygen.

For example, in the extraction of iron from iron ore:

Because redand oxidasi uksi occur at the same time, the above reaction is called

redoxreactions.

Oxidising and reducing agents

Oxidizer or oxidizing agent is a substance that oxidizes another substance. In the

above example, iron (III) oxide is an oxidizer.

Reductant or reducing agent is a substance that reduces another substance. From

the above reaction, the carbon monoxide is the reducing agent.

So it can be concluded:

oxidizer is giving oxygen to other substances,

Reducing agents remove oxygen from another substance

Oxidation and reduction in terms of hydrogen transfer

Definitions of oxidation and reduction in terms of hydrogen transfer has been

long and is now not much used.

Oxidation is loss of hydrogen, reduction is gain of hydrogen.

Note that what happens is the opposite of the oxygen definitions.

For example, ethanol can be oxidized to ethanal:


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To move or remove hydrogen from ethanol required oxidizing agent (oxidant).

Commonly used oxidising agent is potassium dichromate (VI) solution acidified

with dilute sulfuric acid.

Ethanal can also be reduced to ethanol again by adding hydrogen. Reducing agents

which can be used for the reduction reaction is sodium tetrahydridoborate, NaBH4.

Simply put, the reaction can be described as follows:

Oxidizing agent (oxidant) and reducing agent (reductant)

Oxidizing agent (oxidant) to give oxygen to another substance, or remove

hydrogen from other substances.

The reducing agent (reductant) remove oxygen from another substance, or

give hydrogen to other substances.

Oxidation and reduction in terms of electron transfer

Oxidation is loss of electrons, and reduction is gain of electrons.

This definition is very important to remember. There is an easy way to help you

remember this definition. In the case of electron transfer:

A simple example

Redox reactions in terms of electron transfer:

Copper (II) oxide and magnesium oxide are both ionic. Being in the form of non-

metal ions. If this reaction is rewritten as an ionic equation, it io n oxide is the

spectator ions (ions audience).

If you look at the equation above, magnesium is reducing the copper (II) by giving

electrons to neutralize the charge of copper (II).


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It can be said: magnesium is a reducing agent (reductant).

In contrast, the copper ions (II) electron transfer from magnesium to produce

magnesium ions. Thus, copper ions (II) acts as the oxidizing agent (oxidant).

It is rather confusing to study the oxidation and reduction in terms of electron

transfer, and learn the definition of oxidising and reducing agents in terms of

electron transfer.

Can be summarized as follows, oxidiser what role in electron transfer:

Oxidizing agent oxidizes another substance.

Oxidation is loss of electrons (OIL RIG).

That means an oxidising agent takes electrons from another substance.

So an oxidising agent must gain electrons

Or it can be summed up as follows:

An oxidizing agent oxidizes another substance.

That means oxidizing agents should be reduced.

Reduction is gain of electrons (OIL RIG).

So an oxidising agent must gain electrons.

Example:

- The reaction between Na and Cl 2 to form NaCl

In this reaction Na release one electron which is then received by Cl

2Na + Cl2? 2NaCl or Na + Cl2? NaCl

handover electrons occurs:

Na + + e Na removing electrons (oxidation)


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Cl2 + e? Cl Cl accept electrons (reduction)

- The reaction between Ca and Cl 2 to form CaCl2

In this reaction Ca release two electrons which are then received by Cl Ca + Cl2?

CaCl2

handover electrons occurs:

Ca 2+ + 2e removing electrons (oxidation)

Cl2 + 2e? 2Cl- Cl accept electrons (reduction)

3. The concept of redox reactions by changes in oxidation state

In the complex redox reactions will be difficult to determine which atomic

removing or accepting electrons. The chemists overcome this by linking the

oxidation and reduction reactions by oxidation number changes.

In order to implement this concept, we must first understand the definition of the

oxidation numbers and how to determine the oxidation number. After that will be

discussed in oxidation state changes in a redox reaction.

OXIDATION NUMBERS

The oxidation number (bilok or bo) is a number that indicates the charge

contributed by the atoms of the element in the formation of molecules or ions. For

example, the NaCl formed through ionic bonds, the oxidation number of Na is +1

and the oxidation number of Cl is -1. To compound HCl formed by covalent bonds,


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more electropositive H has oxidation number +1, while the more electronegative

Cl has oxidation number -1.

In general, for two bonded atoms are ionic or covalent apply:

- Atomic elements with larger electronegativity will have a negative oxidation

number.

- Atomic elements with smaller electronegativity (more electropositive) have a

positive oxidation number.

The following rules and keeping that can help determine the oxidation number ofan atom.

Rule 1:

Oxidation numbers of atoms in an element is equal to 0 (zero)

Example: bilok atoms on the elements Fe, Na, Cu, H2, Cl2, Br2, I2, O2 = 0

Rule 2:

Monoatom ion oxidation number equal to the charge on the ion.

Example - bilok Fe2 + = +2

- Bilok Na + = +1

- Bilok ion Cl = -1

- Bilok S2- ion = -2

Rule 3:


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The oxidation number of IA group metal (Li, Na, K, Rb, Cs) in the compound =

+1

The oxidation number of group IIA metal (Be, Mg, Ca, Sr, Ba, Ra) in the

compound = + 2

Example - bilok Na in NaOH = +1

- Bilok K in KCl = +1

- Bilok Mg in MgO = +2

- Bilok Ca in CaCl2 = -2

Rule 4:

The oxidation number of H in the compound generally = +1

Numbers oksdasi H in a metal hydride compound = -1

Example - bilok H in HCl, H2O, NH3 = +1

- Bilok H in NaH, CaH2 = -1

Rule 5:

The oxidation number of oxygen (O) in the compound generally = -2 (oxides)

Numbers okidasi oxygen (O) in a peroxide compound = -1

The oxidation number of oxygen (O) in a peroxide compound = -

The oxidation number of oxygen (O) in a binary compound of fluoride = +2


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Example - bilok O in Na2O, CaO = -2

- Bilok O in the NAO, CaO2 = -1

- Bilok 2 O in the NAO, KO2 = -

- Bilok O in OF2 = +2

Rule 6:

The amount of oxidation numbers in a neutral compound = 0

The amount of oxidation numbers in a polyatomic ion = charge on the ion

Example - in the compound H2SO4

2 x bilok bilok H + S + 4 x bilok O = 0

in ion Cr2O7

2 x bilok Cr + 7 x bilok O = -2

By understanding the rules above we can determine the oxidation number of an

atom in a compound or ion.

Example:

Determine the oxidation number of Cl in CaCl2

Bilok Ca = +2 (rule 3)

(Bilok Ca) + (2 x bilok Cl) = 0

2 + (2 x bilok Cl) = 0

bilok Cl = -1


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Determine the oxidation number of S in H2SO4

Bilok H = +1 (rule 4)

Bilok O = -2 (rule 5)

(2 x bilok H) + (bilok S) + (4 x bilok O) = 0 (rule 6)

(2 x 1) + (bilok S) + (4 x (-2)) = 0

2 + bilok S - 8 = 0

bilok S = +6

Determine bilok Cr in Cr2O7

Bilok O = -2 (rule 5)

(2 x bilok Cr) + (7 x bilok O) = -2 (rule 6)

(2 x bilok Cr) + (7 x (-2)) = -2

2 x bilok Cr = 12

bilok Cr = +6

OXIDATION NUMBERS OF CHANGES IN OXIDATION REACTIONS

After understanding how to determine the oxidation number of an atom, we can

determine the oxidation-reduction reactions by oxidation number changes.

Oxidation is increase in oxidation number Reduction is a decrease in oxidation

number. Substances atom of the element undergoes oxidation is called a reductant,

whereas substance atom of the element is reduced is called an oxidizing.

Oxidants are substances that undergo reduction


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Reducing agents are substances that undergo oxidation

Instance

Reactions taking iron ore from the oxide is shown by the following reaction

Fe2O3 + 3CO? 2Fe + 3CO2

a. Determine Which reducible substances and oxidized

b. Determine the oxidizing and reducing agents

Answer:

a. To determine which substances are reduced and oxidized substances follow

these steps:

- Specify each atom bilok

- Specify bilok atoms increased.

- Specify bilok atoms decreased.

Fe2O3 + 3CO? 2Fe + 3CO2

The oxidation number of Fe dropped from +3 to 0, so the reduced Fe2O3 to Fe.

The oxidation number of C increased from +2 to +4, so CO is reduced to

CO2

b. Oxidants are CO, reductant is Fe2O3

Instance


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The following reaction: HI + HNO2? NO + H2O + I2

a. Determine Which reducible substances and oxidized

b. Determine the oxidizing and reducing agents

Answer

a. +3 +1 +1 -1 +1 +2 -2 -2 -2 0

HI + HNO2? NO + H2O + I2

The oxidation number of N fell into +2 +3, so HNO2 reduces to

NO.

I rose from oxidation number -1 to 0, so HI reduces to I2

Disproportionation Reaction And Konproporsionasi

Disproportionation reaction is a redox reaction the oxidizing and

reduktornya is the same substance. So, some of the substances undergo

oxidation and partly reduced.

Example:

Most of the chlorine gas (Cl 2) (oxidation state = 0) was reduced to the NaCl

(Oxidation state = -1) and partly suffered be NaClO oxidation (oxidation state =

+1).

Konproporsionasi reaction is the reverse of the disproportionation reaction, ie

redox reaction in which the reduction and oxidation same results.


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Equalizes REDOX REACTION EQUATION

As with any other chemical changes, oxidation and reduction reactions

also shown by a chemical equation. Because the redox equations also

must be synchronized. Are you able to equalize the reaction corrosion

the iron? Quickly you can certainly get it done.

Now we consider the following redox reaction:

C + HNO3? CO2 + NO2 + H2O,

if you can equalize the reaction? If you equalizes

redox reactions by trial and error, you will often experience

trouble. To simplify equalizes redox reactions, can

using the oxidation number method and the half-reaction method. Each

The method includes the steps that can guide you

equalizes the redox reaction. This way you have to remember that

chemical equations can be added, subtracted, and multiplied.

HOW TO OXIDATION NUMBERS

To balance redox reactions by means of oxidation numbers,

you should be able to determine the oxidation number of the elements that exist

within a

compounds. If you already understand how to determine oxidation numbers,


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You can easily equalizes redox reactions. Steps

in equation equalizes the redox reaction by means of oxidation numbers

are:

Step 1: Balance the number of elements, other than O and H, are experiencing

changes in oxidation state by giving coefficient.

Step 2: Determine the oxidation and reduction reactions in a way

write the change in oxidation number.

Step 3: Keep the same number of electrons received and released

by multiplying by a certain number.

Step 4: Balance the oxygen by adding H2O.

Step 5: Balance the hydrogen by adding H +.

Kim. 07. Reduction and Oxidation Reactions 15

To be more clear, consider the following example to balance the reaction:

MnO4

- + Cl ?? Mn2 + + Cl2

Step 1

MnO4

- + 2Cl-? Mn2 + + Cl2

On the right hand side artifacts 2 Cl atom, so that the Cl on the left given the

coefficient 2


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Step 2

MnO4

- + 2Cl-? Mn2 + + Cl2

+7 2x (-1) +2 0

The change in oxidation state of Mn + 2 = 5 + 7 become

The change in oxidation state of Cl 2x (-1) to 0 = 2

Step 3

2MnO4

- + 10Cl- ?? 2Mn2 + + 5Cl2

The number of electrons received Mn = 5 and electrons are released Cl = 2. That

received the same number of electrons with the electrons removed, then Mn

multiplied by 2 and multiplied Cl 5.

Step 4

2MnO4

- + 10Cl- + 16H + ?? 2Mn2 + + 5Cl2 + 8H2O

On the left side there are eight oxygen atoms from 2MnO4

-, Add 8H2O in segment

right. As a result of the addition of H2O, in the right-hand side there are 16

hydrogen atoms

of 8H2O, add 16H + on the left.


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Now you try to count the number of each atom contained in

the left side and the right side, whether it is equivalent ?. Then calculate also

the charge on the left and right, is it the same? If the number of atoms and charge

on the left and right of the redox reaction is equivalent.

You have studied the concept of acids and bases, now

note that it is equivalent reaction above. In such reactions are ion

H + on the left, what does it mean? The presence of H + ions showed that the

reaction

takes place in acidic conditions.

You certainly questioned, what if the reaction takes place at

alkaline? To balance the redox reaction in alkaline conditions, can

done by neutralizing the H + ions in the last step with OH- ions

(H + + OH-? H2O). Add OH-on the left and right as many H + ions.

To obtain a clearer picture note the following example.

Cl2 + IO3 -? IO4

- + Cl (alkaline)

If you follow steps 1 through 5 will be obtained:

Cl2 + IO3

- + H2O? IO4

- + 2H + + 2Cl-


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To change into alkaline, add 2OH- on both sides.

On the right side there will be a neutralization reaction 2H + + 2OH-? 2H2O

Cl2 + IO3

- + H2O? IO4

- + 2H + + 2Cl-

2OH- 2OHCl2

+ IO3

- + H2O + 2OH- ?? IO4

- + 2Cl- + 2H2O

Cl2 + IO3

- + 2OH-? IO4

- + 2Cl- + H2O

HOW TO HALF REACTION

To balance redox reactions by means of half-reactions follow

the following steps:

Step 1: Separate the redox reaction becomes the reduction reaction and the reaction

oxidation.

Step 2: Balance the number of elements, other than O and H, are experiencing

changes in oxidation state by giving coefficient.


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Step 3: Add H2O to balance the oxygen atoms and

Kim. 07. Reduction and Oxidation Reactions 17

add H + to balance hydrogen atoms.

Step 4: Add electrons to balance the charge.

Step 5: Equalize the number of electrons released in the reaction

oxidation of the number of electrons received at the reaction

reduction, then add the two reactions.

For example, Balance the following redox reaction

Cr2O7

2- + Fe 2+ ?? Cr 3+ + Fe 3+ (acid)

Step 1

Cr2O7

2-? Cr3 +

Fe2 +? Fe3 +

Step 2

Cr2O7

2-? 2Cr3 +

Fe2 +? Fe3 +

In the reduction reaction of Cr number on the left is 2, then on the right side ion


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CR2 + given a coefficient of 2, whereas the amount of Fe oxidation reaction on the

left

and right alike, then no need to increase the coefficient

Step 3

Cr2O7

2- + 14H +? 2Cr3 + + 7H2O

Fe2 +? Fe3 +

In the reduction reaction, the amount of O in Cr2O7

2- is 7, then on the right side

7 H2O should be added, due to the addition of 7H2O in the next section

Right there are 14 H atoms, then on the left need to plus 14 H +. On

no oxidation reaction of O atoms, so that no additional

H2O and H +.

Step 4

Cr2O7

2- + 14H + + 6e-? 2Cr3 + + 7H2O

Fe2 +? Fe3 + + e-

In the reduction reaction of the charge on the left is -2 + 14 = 12, the number of

charge on the right side is 2 x 3 + 0 = 6. In order to charge the same on the left

plus 6 e.


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In the oxidation reaction the amount of charge on the left = 2 and on the right side

= 3,

then on the right side plus 1e-.

Step 5

Cr2O7

2- + 14H + + 6e-? 2Cr3 + + 7H2O

6Fe2 +? 6Fe3 + + 6e-

Cr2O7

2- + 14H + + 6Fe2 +? 2Cr3 + + 7H2O + 6Fe3 +

In the reduction reaction the number of electrons = 6 whereas the oxidation

reaction

number of electrons 1, then the oxidation reaction must be multiplied by six.

Now if you try to count the number of atoms and the number of charges,

whether the reaction is equivalent?

To equalize the redox reaction under alkaline conditions can

performed as described in oxidation number, which neutralizes H + with

OH-in the final stages.


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Combustion Reaction

Substances around us there are that have a flammable nature, and nature is not

can burn. Any substance that can burn fuel will have a point each.

A substance will burn by itself when the agent reaches the point of fuel

due to heating. Burning substance actually involves a reaction between the

substance

with oxygen gas (O2).

Therefore, the combustion event can only happen because of the two

factors, namely materials (substances) that can be burned and the factor of oxygen

gas.

Thus, the combustion can be avoided by lowering the burning point

substances (flush with water or certain chemicals), or by blocking

Basic Concepts of Chemistry for PGSD 139


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materials / substances come into contact with oxygen gas. Or vice versa, so that

the combustion occurs,

materials / substances to the point where the temperature is raised in the fuel gas

of sufficient oxygen.

Materials / substances that burn will result in the form of oxide compounds. Kind

oxide is dependent on the type of elements that make up the material / substance

concerned. Note Table 1.

The content of ROHP

Elements of H H2O vapor

Elements of C Gas CO; CO2

Elements of S SO2 gas; SO3 gas

Elements of P Gas P2O5

Of N NO2

Table 1

Oxide Formula Combustion (ROHP) of Material / Substance That Can Be Burned

Substances such as hydrogen gas (H2), phosphorus (P4), sulfur (S8), or carbon (C)

when burned

will produce the gases listed in Table 6.1. Materials / substances there are

contains several types of content listed, such as C and H. Example

This compound is methane (CH4), acetylene (C2H2), liquefied petroleum gas

when burned will

produce H2O vapor and CO2. On other occasions, there are materials / substances


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contains simultaneously multiple types of content elements C, H, and O. Examples

of compounds

These include glucose, C6H12O6; sugar, C12H22O11; or alcohol, C2H5OH. And

when

burning will produce CO2 and H2O vapor.

Thus, it can be stated that the burning substance means a substance that reacts

with oxygen. Combustion reaction of the substances mentioned above can be

expressed

as follows.

C + O2 CO

C + O2 CO2

2 H2 + O2 2 H2O

P4 + 5 O2 2 P2O5

C6H12O6 + 6 O2 6 CO2 + 6 H2O

Combustion can be distinguished by the complete combustion and combustion

perfect. Combustion is considered complete if the entire elemental components

transformed into the highest oxide components such as H H2O; C CO2;

S SO3; or P P2O5. Other results in the form of lower oxides, indicating that

combustion is incomplete combustion. Usually combustion

perfect place in the small amount of oxygen (less).


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3. Calculation of Heat of Combustion

Any substance that can be burned (or oxidized) to release a number of

called calorific fuels. The fuel will be burned after reaching the point of fuel,

further combustion takes place by itself (spontaneous) in oxygen

enough. Own reaction called combustion reaction, and the heat liberated is called

heat of combustion. Fuel value is often determined by the value of heat of

combustion of

fuel in question in addition to other factors such as economic value, practicality

its use, and its impact.

Oxidising And Reducing agents

1. Definition of oxidizing and reducing agent

Oxidants (oxidizing) is a substance that causes oxidation

on a substance (or substances that decrease BO). Instead reductant

is a substance that plays a role in the reduction of another substance (or substances

that undergo

raising BO).

Examples of oxidizing and reducing agents:

(A) Cl + Cl 1e- (reduction reaction)

(B) O + 2e O2 (reduction reaction)


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oxidizing

(C) Na Na + + 1e- (oxidation)

(D) Ca 2+ + 2e (oxidation)

reductant

(E) Ca + O CaO (redox reaction)

(F) Fe + H2SO4 FeSO4 + H2 (redox reaction)

reducing agent oxidizer

Explanation:

Raising BO

+2 -2

Ca + O CaO

Decrease BO

0 +2 +2 0

Fe + H2SO4 FeSO4 + H2

reducing agent oxidizer


Reducing agents = reducing agent.

Y = substance. release electrons.

Y = substance. experienced an increase of BO


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Oxidants = oxidizing agent.

Y = substance. binding electrons.

Y = substance. decreased BO.

2. Nature of Oxidising And Reducing agents

Ability to oxidize oxidizer (also reductant in reducing)

different. Known to have a strong oxidizer or oxidant weak; as well as reducing

agent.

Several oxidizing strength can be estimated on the basis of, among others,

ease in releasing electrons; while the reductant of simplicity

the electron binding. To illustrate the nature of oxidizing or reducing agent

properties,

we limit the discussion to the alkali metals (Li, Na, K, Rb); and halogen (F, Cl, Br,

I).

The nature of the two classes of elements, such as alkali elements (M) and halogens

(X2) is:

M M + + e- and X2 + e- 2 X

alkali elements the halogens

From the nature of the reaction, alkali or alkali metal element is as a reducing

agent,

and alkali element is as an oxidant. Quickly it can be concluded that the elements


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alkali (alkali metal, M) is the most powerful reducing agent; whereas the halogens

(X2)

is the most powerful oxidizer. Why?

Inter alkali metal (M) itself, the Li metal was the one most difficult to let go

valence electrons whereas Rb metal easiest release valence electrons.

Thus, Li metal is the weakest reducing agent; otherwise metal Rb

is the strongest reducing agent among the alkali metals.

Another case with a halogen (X2), then the most powerful electron binding ability

among group elements are elements of F2. Means the halogen group, an element

of F2

is the most powerful oxidizer, and the elements of I2 is the weakest oxidizing.

From the foregoing, it is clear that the elements between the two groups (alkali

and halogen) most easily react with each other to form ionic compounds.

Consider the two following redox reaction:

2 Li + Cl 2 2 LiCl

2 Na + Cl 2 2 NaCl

Which reaction will easily take place?

Due to the nature of the reductant metal is stronger than metal Na Li, the second

reaction

which would be easier to take place.


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So by knowing the nature of the oxidant and reductant of a redox properties, we

can

estimate the ease of redox reactions that take place.

3. Reaction Autoredoks

Redox reactions discussed above involves two types of substances which are

one acts as a reducing agent and the other acts as a reducing agent. Types

Other redox reaction in which a substance acts as well as reducing and

oxidant. The reaction is called a redox reaction or reaction autoredoks

disproportionation.


In the following reaction indicated that the Cl2 acts as well as reducing and

oxidant.

NaOH + Cl2 NaClO + NaCl + H2O

Why does this reaction belong autoredoks reaction? Really Cl2 acts as well as

reductant and oxidant? Note the following explanation.

IUPAC nomenclature based on

1. Ion Binary Compounds (IA and IIA Metal goi + nonmetal + ida)

KCl = potassium chloride

oxides Na2O = Sodium

Magnesium bromide MgBr2 = 2. Ion Binary Compounds (Metal + metal +

nonmetal oxidation number + ida) FeO = Iron (II) oxide / Fero chloride FeCl3 =

Iron (III) chloride / Ferry chloride CuCl = Copper (I) chloride CuO = Copper (II)


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oxide 3. Covalent Compounds (atomic number + number + nonmetal + nonmetal

atoms) N2O5 = dinitrogen pentaoksida / nitrogen (V) oxide NO = nitrogen

monoxide / nitrogen (II) oxide SO2 = sulfur dioxide / sulfur (IV) oxide Cl2O3

dichloro = trioxide / chlorine ( III) oxide

Summary

The concept of redox reactions based on the incorporation and release of oxygen.

Oxidation is the combination of oxygen with an element or compound.

Reduction is the release of oxygen from compounds.

The concept of redox reactions based on the incorporation and release of electrons.

Oxidation is the release of electrons.

Reduction is the electron acceptance.

The concept of redox reactions by oxidation number changes.

Oxidation is increase in oxidation number.

Reduction is a decrease in oxidation number.

Substances atom of the element undergoes oxidation is called reducing agent,

whereas substance atom of the element is reduced is called an oxidizing.

Oxidants are substances that undergo reduction.

Reducing agents are substances that undergo oxidation.

The oxidation number (bilok or bo) is a number that indicates

charge contributed by the atoms of the element in a molecule or ions are formed.


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There are two ways to balance a redox reaction equation, namely how oxidation

numbers and half-reaction method.

TWO IDEAS OF THE REDOX REACTION: MISCONCEPTIONS AND

THEIR CHALLENGE IN CHEMISTRY EDUCATION

In modern chemistry education the redox reaction is defined by an electron

transfer, as

illustrated with a metal-nonmetal reaction (see Fig. 1), or with the reaction of iron

and a copper

sulfate solution (see Fig. 2).

Fig. 1: Model of the reaction of metal atoms with nonmetal atoms by electron

transfer (1)

In these examples, the reactions can be explained by electron transfer from metal

atoms


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Fig. 3: Model drawing of the reaction of Cl2 molecules with I-(aq) ions, K+(aq)ions remain as spectator ions (2)

PREVENTION OF HOMEMADE MISCONCEPTIONS

According to the poor results by teaching the redox idea one likes to state:

"disregard the

simple redox idea of oxygen transfer from school curricula and school books".

Considering that

in so-called oxygen-transfersfor example in the reaction of copper oxide with

ironoxygen

atoms are not transferred, but iron atoms release electrons to copper ions and the

oxide ions

change only the ionic lattice, so the emphasis on "the oxygen" is not justified:

neither oxygen is

AJCE, 2012, 2(2).


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transferred, nor O atoms change their partner. If the redox idea would only be

taught as an

electron transfer from one particle to another, then instruction and results should

improve

dramatically.

Historical redox idea. Since this idea is prescribed in all guidelines and school

books, one must

consider ways of instruction that are touching the extended redox idea as little as

possible.

There is first the historically evolved definition: teachers or students can refer

Stahls Phlogiston

theory from 1690 and its refutation by the Oxidation theory of Lavoisier in 1784.

Students can

understand that historically adapted theories have been rejected later and replaced

or extended by

new theories. In their own classes, they can accept that the extension of the

oxygen transfer to

the electron transfer is legitimate.

On the other hand, in the beginning one could instruct this subject without the word

redox and use it only in the extended sense. Since oxidation (metal + oxygen

metal oxide)

and reduction (silver oxide silver + oxygen) are initially defined separately, the

redox idea

appears dispensable; the notation for the copper oxide-iron reaction is sufficient in

this way: iron

is oxidized to iron oxide, copper oxide is reduced to copper. Then, if the reaction

is described

only in words, one cannot get into difficulties with "O atoms, O2 molecules or O2-

ions are

changing the partner". Choosing a model drawing to show the regrouping of

particles in the


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copper oxide-carbon reaction for example, you can explain the "combination of

carbon particles

with the oxygen particles and the release of copper particles" (Fig. 4).

Fig. 4: Model drawing for the reaction of copper oxide with carbon (1)

Fig. 5: Macro, sub-micro and representational level in chemistry education (11)

Given the decrease in mass, a sensible name for the process was made: reduction.


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In what world does it make sense to call a process where electrons are gained

reduction ?

The answer from my high school chemistry teacher was , well, youre reducing

the oxidation statemaking it more negative. Which was a very clever answer,

completely jettisoning the inconvenient historical definition in favor of a simplistic

mathematical one. Fortunately for him, I wasnt fast or clever enough to counter

with then why isnt oxidation called addition? (Feel free to use this yourself,

however).

Result: I just memorized that reduction meant adding electrons and

oxidation meant removing electrons. Which came in handy in general

chemistry, with its seemingly endless balancing of complex redox reactions.

Just when this seemed settled in my mind, along came organic chemistry, with

what was seemingly yet another way of defining oxidation and reduction. Agh!!!

At first glance, this seems a long way away from the Gen chem definition of

oxidation being loss of electrons and reduction a gain of electrons.

But if you go back to the concept of the oxidation state, it might make some more

sense. If you just pay attention to whats happening to the oxidation state of the
http://masterorganicchemistry.files.wordpress.com/2011/07/redox-1-copy.jpg


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carbons, you can follow along to see if its an oxidation or reduction. If the

oxidation state is becoming more negative, its a reduction (gaining electrons). If

the oxidation state is becoming more positive, its an oxidation (losing electrons).

Lets look at those examples again (putting in an extra example for fun), paying

attention to the change in oxidation state.

So is there a quick way to figure out if a carbon is being oxidized or reduced? Why

yes there is.

A reductionwill result in a net increase in the number of C-H bonds, or a net

decrease in the number of C-O bonds(or equivalent, such as C-Cl, C-Br, etc).
http://jamesash.wpengine.netdna-cdn.com/wp-content/uploads/2011/07/ox-red-copy.jpghttp://jamesash.wpengine.netdna-cdn.com/wp-content/uploads/2011/07/4-redox-copy.jpg


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An oxidationwill result in a net decrease in the number of C-H bonds,or a net

increase in the number of C-O bonds (or equivalent).

All of these events affect the oxidation stateof the carbon, and this ties back to

the concept of oxidation that I originally learned in high school: keeping track of

the gaining (and losing) of electrons.

When I finally understood this I was happy to note that the term oxidation finally

made sense again.

Reduction still didnt, but I learned to live with it and moved on. You will too.

PHOTOSYNTHSIS

Photosynthesis is a word derived from the Greek, ie photos and synthesis. Photo

itself is defined as a light while synthesis is a meaningful word combining or

merging. The word is often used in scope photosynthesis study biological sciences.

What exactly is photosynthesis? Simply put, it can be defined as the process of

making food that is made by green plants involving sunlight in it. In addition tothe sun, photosynthesis process also involves several enzymes. The process of

photosynthesis is usually carried out by plants, algae and some kinds of bacteria in

order to produce the energy that will be used in a variety of activities. The energy

is also called nutrients.

The leaves on the plant has a primary function as the site of photosynthesis.

Actually, not only important for the photosynthesis of plants but also for all the

living creatures that inhabit the earth. Why? Because the oxygen that is in the earth

is mostly produced by plants. This is what makes trees often nicknamed lungs of

the planet earth. Organisms that perform photosynthesis known as Phototroph.

Photosynthesis is actually one way of carbon assimilation because in the process

of photosynthesis, carbon-free and then tied that into sugar.

The process of photosynthesis in green plants found in nature that autotrophs can


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prepare their own food. Through the leaves, plants absorb carbon dioxide

molecules are also water in order to produce sugar and oxygen. Both of these

compounds will then be used as a backstop growing. The equation reaction that

occur in the process of photosynthesis is as follows:

6H2O + 6CO2 + light C6H12O6 (glucose) + 6O2

Plants that perform photosynthesis requires sunlight assistance. They are able to

absorb the light because they have a green substance or chlorophyll. Chlorophyll

itself is in organelles called chloroplasts section. On the leaves of plants, there are

two layers of cells called mesophyll denegan. in this section there are

approximately half a million chloroplasts scattered in every square millimeter.

Sunlight will then pass through the epidermal layer of colorless then drove towards

the mesophyll. In this section most of the photosynthetic activity takes place.

The process of photosynthesis itself is quite complex and is still in the research to

some experts. There are still many things that have not been successfully

expressed. Why this complex process? Because it involves almost all branches of

science, for example bilologi, chemistry and physics. The main organ where

photosynthesis is exactly in the stomata of the leaves or leaf mouth. The process

of photosynthesis consists of two series of reactions that the light reaction and a

dark reaction. Named because the light reaction process takes light. While it is a

dark photosynthesis reaction process that no longer involves the light but only

carbon dioxide.

In the process photosynthesis, light reaction is a process that ultimately produces

ATP also NADPH2. In the reaction of water molecules necessary. The process

begins by capturing the light reaction photons carried by the pigment chlorophyll

which acts as an antenna. In the leaves, the light will be absorbed by chlorophyll


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molecules and then collected at the reaction centers. Photosynthesis begins when

light begin to ionize molecules of chlorophyll and then the release of electrons.

Application of Redox Reactions in Everyday Life Redox

1. metal reaction in Processing concentrating are from the rock either physics or

chemistry then concentrated into a concentrated ore. The concentrated ore is

reduced with a reducing agent most appropriate.

3C (S) + 4Al3 + (l) + 6O-2 (l) --> 4AL (l) + 3CO2

reduction reaction

Redox 2.Reaksi In BesiRel Splicing-thermite welded rail with the process. A

mixture of aluminum and iron oxide for redox reactions ignited to heat and can

melt the surface generated rel.Reaksi:

2AL (s) + Fe2O3 (S) --> 2Fe (s) + Al2O3 (s)

Redox 3.Reaksi On Cell Battery

Pb (s) + PbO2 (aq) + 2HSO4-2 (aq) + 2H + (aq) --> 2PbSO4 (S) + 2H2O (l)

At 4.Reaksi redox battery (cell Leclanche)

Zn (s) + 2NH4 + (aq) + 2MnO2 (S) --> Zn 2+ (aq) + Mn2O3 (s) + 2NH3 (aq) +

H2O (l)

Redox 5.Reaksi In Wastewater Treatment

Electrolytes concept a.Penerapan Waste containing heavy metal (Hg + 2, Pb + 2,

Cd + 2, and Ca 2+) were reacted denganelektrolit mengndung anion (SO4-2) which

can precipitate the metal ions so that the waste water is free from water limbahPb

+ 2 (aq) + SO4-2 (aq) PbSO4 --> (S)


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b.Ph Libahan LuurAkTi Luurakti teriaerb teribak containing tub that serves as

inorganic oksidatorbah terarut without the use of oxygen in the water so that the

price can be in kurangi.Zat atorganik BOD in menjadiCO2 oxidation, H2O, NH4

+ and new cell biomass. Lumpurakt process takes place in the aeration tank. In that

pool lasts oxidation of organic wastes (carbohydrate, protein, oil). Results organi

oxidation compounds are CO2, H2O, sulfate, nitrate, and phosphate. Oxygen is

obtained for olsidasi obtained from the photosynthesis process algae that live

ditangki aeration

Redox 6.Reaksi On Cell Volta (Cells Galvani) electro-chemical cells where

oxidation - reduction occurs spontaneously and produces a potential difference dI

called galvanic cell. In a galvanic cell chemical energy is converted into electrical

energy. Selgalvani also often called Volta cells. Examples baterai.Energi galvanic

cell is a cell that is in the release can be used to turn on the radio to connect a wire

from the electrode to the radio. Whole-cell copper-magnesium reaction is a redox

reaction.

Mg (s) + Cu 2+ (aq)Mg2 + (aq) + Cu (s)

Is the function of the salt bridge? When the half-reaction continues, magnesium

ions released into the solution at the anode, and copper ions move to the cathode.

Ions should be able to move both electrodes equal freedom to neutralize the

positive charge (cation Mg 2+) generated at the anode and the negative charge

(anions) are left at the cathode. Solution of the ions in the salt bridge can neutralize

the positive and negative charges in solution and prevent excess charge on the

electrode. The same redox reaction occurs when magnesium metal is put directly

in the solution of copper sulfate, the reaction is

Mg + Cu 2+ Cu ++-->Mg2.

However, this is not because the galvanic cell electrons flow through the circuit

luar.Elektron not move directly from magnesium metal ions to the copper, forming


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copper metal. This is how to make copper metal from copper ions, but not for the

generation of electricity.

Redox Reaction In Natural Gas If natural gas is burned, it will establish the

following reaction

CH4 (g) + 2O2 (g)CO2 (g) + 2H2O (g)

Redox reaction in Biological cells, for example, is the oxidation of glucose

(C6H12O6) into CO2 and oxygen to water reduction. Concise equation of cell

respiration is: C6H12O6 + 6 CO2 + 6 O2 6 H2O

oxidation and reduction.pdf

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