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Redox Reactions. Reduction. Oxidation. GCSE. Oxidation : Gain of oxygen Loss of electrons. Reduction : Loss of oxygen Gain of electrons. Increase in oxidation number. Decrease in oxidation number. 4 Experiments:. Burning magnesium Copper in silver nitrate solution

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redox reactions

Redox Reactions.

Reduction

Oxidation

slide2
GCSE
  • Oxidation:
  • Gain of oxygen
  • Loss of electrons
  • Reduction:
  • Loss of oxygen
  • Gain of electrons

Increase in

oxidation

number

Decrease in

oxidation

number

4 experiments
4 Experiments:
  • Burning magnesium
  • Copper in silver nitrate solution
  • Chlorine solution and potassium iodide solution
  • Exploding hydrogen
  • Word equation
  • Balanced symbol equation
2mg s o 2 g 2mgo s

Oxidised – gains oxygen

2Mg(s) + O2(g)  2MgO(s)

Must be a redox!

Mg  Mg2+

Oxidised – loss of e-

+2e-

Put the

e- in.

O  O2-

Reduced – gain of e-

+2e-

cu s 2agno 3 aq cu no 3 2 aq 2ag s
Cu(s) + 2AgNO3(aq)  Cu(NO3 )2(aq) + 2Ag(s)

Complete the half-equations

Oxidised?

Reduced?

Cu  Cu2+

Oxidised – loss of e-

+2e-

Ag+ Ag

Reduced – gain of e-

+e-

h 2 g o 2 g h 2 o g
H2(g) + ½ O2(g)H2O(g)

Covalent!

Need a new

definition.

No H+ or OH-

slide8
GCSE
  • Oxidation:
  • Gain of oxygen
  • Loss of electrons
  • Reduction:
  • Loss of oxygen
  • Gain of electrons

Increase in

oxidation

number

Decrease in

oxidation

number

oxidation numbers
Oxidation Numbers
  • The oxidation number of an atom in an element is zero. E.g. Mg in Mg, O in O2.
oxidation numbers10
Oxidation Numbers
  • The oxidation numbers of atoms in a compound add up to zero.

Oxidation state of C in CO2?

? – 4 = 0

? = +4

Put the +!

oxidation numbers11
Oxidation Numbers
  • The oxidation numbers of atoms in a compound add up to zero.

Oxidation state of Mg in MgCl2?

+2

oxidation numbers12
Oxidation Numbers
  • The oxidation numbers of atoms in a compound add up to zero.

Oxidation state of N in NH3?

-3

oxidation numbers13
Oxidation Numbers
  • The oxidation numbers of atoms in an ion add up to the charge on the ion.

Oxidation state of S in SO42-?

? – 8 = -2

? = +6

oxidation numbers14
Oxidation Numbers
  • The oxidation numbers of atoms in an ion add up to the charge on the ion.

Oxidation state of S in S2-?

-2

oxidation numbers15
Oxidation Numbers
  • The oxidation numbers of atoms in an ion add up to the charge on the ion.

Oxidation state of N in NH4+?

-3

h 2 g o 2 g h 2 o g17
H2(g) + ½ O2(g)H2O(g)

Covalent!

Need a new

definition.

No H+ or OH-

slide18
GCSE
  • Oxidation:
  • Gain of oxygen
  • Loss of electrons
  • Reduction:
  • Loss of oxygen
  • Gain of electrons

Increase in

oxidation

number

Decrease in

oxidation

number

h 2 g o 2 g h 2 o g19
H2(g) + ½ O2(g)H2O(g)

H

Covalent!

+1

0

O

0

-2

Need a new

definition.

No H+ or OH-

h 2 g o 2 g h 2 o g20
H2(g) + ½ O2(g)H2O(g)

H

+1

0

O

0

-2

Oxidised?

Reduced?

O – decrease

in oxidation

number

H – increase

in oxidation

number

oxidation numbers and names
Oxidation Numbers and names
  • To avoid any confusion when an element can have several oxidation numbers, the oxidation number is usually mentioned in the compound’s name. In names like “elementate(X)”, the number refers to “element” and not the associated oxygens.
  • So if we look at some examples , we get the following names:-

KMnO4 potassium manganate(VII)

NaClO3 sodium chlorate(V)

POCl2F phosphorus(V) oxydichlorofluoride

NaH2PO3 sodium dihydrogenphosphate(III)

K2Cr2O7 potassium dichromate(VI)

Check the

numbers.

slide25

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