REDOX REACTION

REAKSI REDOKS

CHAPTER 6

Teaching Learning Objectivers

• The student can explain definition of redox reactions the first concept (the release and uptake of atoms concept)

• The student can explain definition of redox reactions the secon concept (the electrons transfer concept)

• The student can explain definition of redox reactions the third concept (the change in oxidation number concept)

1.The First Redox Concept,The Release and Uptake of Oxygen atoms Concept

24Na(s) + O2(g)→ Na2O(s)

Cl2(g) + O2(g) → Cl2O3(g)23FeS2(s)+ O2(g)→ Fe2O3(s) + SO2(g)4 2

C2H2(g) + O2(g) → CO2(g) + H2O2 25

•Oxidation reaction is subtance uptakes an oxygen molecule on the reaction.Example :

2811

4

•Reduction reaction is subtance releases an oxygen molecule on the reaction.

Example :

HgO(s)→ Hg(s)+ O2(g)2 2

KClO3(s)→ KCl(s)+ O2(g)32 2

CO2(g)+ H2O(l)→C6H12O6(s)+ O2(g)6 6 6

Fe2O3(s)+ C(s)→ Fe(s)+ CO2(g)32 43

2.The Second Redox Cncept,The Electrons Transfer Concept

•Oxidation reaction is refers to the loss of electrons.

Example :

11Na2 8 1 2 8

Na → Na+ + eNa++ e

12Mg2 8 2

Mg2+

2 8

+ 2e Mg → Mg+2 + 2e

•Reduction reaction is refers to the gain of electrons.

Example :

17Cl2 8 7

+ e Cl-

2 8 8

Cl2 + 2e 2Cl-

8O2 6

+ 2e O2-

2 8

O2 + 4e 2O2-

Reaksi oksidasi selalu diikuti reaksi reduksi :

Na → Na+ + eR. Oks:

Cl2 + 2e→2Cl-R. Red:x2

x1

2Na →2Na+ +2 e

Cl2 + 2e→2Cl-

2Na + Cl2→2Na+ + 2Cl-R.Redoks :2NaCl

Mg → Mg+2 + 2eR. Oks:

R. Red: O2 + 4e→2O-2

x2

x1

2Mg →2Mg+2 + 4e

O2 + 4e → 2O-2

2Mg +O2 →2Mg+2 +2O-2

2MgO

R.Redoks :

The Rules to determine the okxidation numbers

1. The oxidation numbers of free are zero

2. The oxidation numbers of mono atomic ion are equals to its ionic charge,

3. The sums of oxidation numbers of atoms in their coumpounds are zero.

4. The sums oxidation numbers is poliatomic ions are equal to the charge of poliatomic ions.

5. The oxidation numbers of group IA element in a compound is +1, while the oxidation numbers of group.

IIA element in a compound is +2

6. The oxidation numbers of group VIIA element in a compound is -1.

7. The oxidation numbers of hydrogen atom in compound is +1, exept in metal hydride its the oxidation numbers is -1.

8. The oxidation numbers of oxygen atom in compound is -2, exept in peroxide, its oxidation numbers is -1. And the oxidation numbers in binary compound with flourine is +2.

1.The oxidation numbers of free are zeroExample :

Na BO = 0 Al BO = 0 F2 BO =0 S8 BO =02. The oxidation numbers of mono atomic ion are

equals to its ionic charge,Example :

Na+ BO = +1 Al+3 BO = +3 Cl- BO = -1 O-2 BO = -2

3. The sums of oxidation numbers of atoms in their coumpounds are zero.

Example :

5.The oxidation numbers of group IA element in a compound is +1, while the oxidation numbers of group.

6. The oxidation numbers of group VIIA element in a compound is -1.

NaCl

(+1)

MgBr2 Na +Cl = 0

(-1) + = 0

Mg +2Br = 0 (+2) + 2(-1) = 0

IIA element in a compound is +2

7.The oxidation numbers of hydrogen atom in compound is +1, exept in metal hydride its the oxidation numbers is -1.

8. The oxidation numbers of oxygen atom in compound is -2, exept in peroxide, its oxidation numbers is -1. Example :

H2O Na + H = 0

2(+1) + (-2) = 0

Exept (7) : NaH 2H + O = 0

(+1) + H = 0

H= -1

CaH2 Ca + 2H = 0 (+2) + 2H = 0

H= -1

Exept (8) :

H2O2

Na2O2

2H + 2O = 0 2(+1) + 2O = 0

2O = -2 O = -1 BaO2

4.The sums oxidation numbers is poliatomic ions are equal to the charge of poliatomic ions.

Example :

SO4-2 S + 4O = -2

S + 4(-2) = -2 S = -2 + 8 S = +6

KClO3 K + Cl + 3O = 0

(+1)+ Cl +3(-2) = 0

Cl = +5

Exept (6) :Gol VIIA yang mengandung atom O dalam senyawanya BO tidak -1

3.The Third Redox Concept,The Change in Oxidation Number Concept •Oxidation reaction is the increasing oxidation number.

Example: :

•Reduction reaction is the decreasing oxidation number.•Oxidant : being reduced•Reductant : being oxidized

2Na + Cl2→2NaCl0 0 +1 -1

R.OksidasiR.Reduksi

Na Reduktor Cl2 Oksidator

Mg +2HCl → MgCl2 + H2

0 0+1 -1 -1+2

R. OksidasiR. Reduksi

Mg Reduktor HCl Oksidator

Cl2 + KOH→ KCl + KClO3 + H2O0 +1+1 +1 +5+1 -2-2 +1-1 -2

R. Oksidasi

R. Reduksi

MgCl2 Hasil Oksidasi

H2 Hasil reduksi

KClO3 Hasil Oksidasi KCl Hasil reduksi

Reaksi Auto Redoks /

Reaksi

Disproporsionasi