Variable oxidation states
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Variable Oxidation States. Objectives. Be able to... Determine whether elements have been oxidised or reduced in chemical reactions Confidently use half equations to describe redox reactions

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Variable Oxidation States

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Variable Oxidation States


Objectives

Be able to...

  • Determine whether elements have been oxidised or reduced in chemical reactions

  • Confidently use half equations to describe redox reactions

  • Describe how D-block elements can form a variety of oxidation states producing compounds of different colours


Specification...Where this comes from...


HALF REACTIONS

Write both half reactions for the following reaction:

Cu + AgNO3 Cu(NO3)2 + Ag

Reduction:

Ag+ Ag

Ag+ + 1e- Ag

Oxidation:

Cu  Cu+2

Cu  Cu+2 +2e-

Cu -2e-  Cu+2


HALF REACTIONS

Write both half reactions for the following reaction:

HNO3 + I2  HIO3 + NO2

Reduction:

N+5 N+4

N+5 + 1e- N+4

Oxidation:

I20 I+5

I20 2I+5 +10e-

I20 -10e-  2I+5


Half Reactions

Write both half reactions for the following reaction:

Sn + 2AgNO3  Sn(NO3)2 + 2Ag

Reduction:

Ag+1 Ag0

Ag+1 + 1e- Ag0

Oxidation:

Sn0 Sn+2

Sn0 Sn+2 +2e-

Sn0 -2e-  Sn+2


  • Use the changes in oxidation numbers to identify which atoms are oxidized, and which atoms are reduced:

    • 2H2 (g) + O2 (g)  2H2O (l)

    • 2KNO3 (s)  2KNO2 (s) + O2 (g)

    • NH4NO3 (s)  N2 (g) + 2H2O (g)

      • (HINT: consider each N separately)

  • PbO2 (aq) + 4HI (aq)  I2 (aq) + PbI2 (s) + 2H2O (l)


And some more...


Variable Oxidation States

  • One of the most striking properties

  • variable oxidation states

  • The 3d and 4s electrons are

  • insimilarenergy levels

  • availablefor bonding


Variable Oxidation States

  • Elements of the first transition series

  • form ions of roughly the same stability by losingdifferentnumbersofthe 3d and 4s electrons


Oxidation states of the elements of the first transition series in their oxides and chlorides


Oxidation states of the elements of the first transition series in their compounds


1.Scandium and zinc do not exhibit variable oxidation states

  • Scandiumof the oxidation state +3

  • the stable electronic configuration of argon (i.e. 1s22s22p63s23p6)

  • Zinc of the oxidation state +2

  • the stable electronic configuration of [Ar] 3d10


2.(a)All elements of the first transition series (except Sc) can show an oxidation state of +2

(b)All elements of the first transition series (except Zn) can show an oxidation state of +3


3.Manganese has the highest oxidation state +7

E.g. MnO4-, Mn2O7

Mn7+ ions do not exist.


The +7 state of Mn does not mean that all 3d and 4s electrons are removed from Mn to give Mn7+.

Instead, Mn forms covalent bonds with oxygen atoms by making use of its half filled orbitals


Draw the structure of Mn2O7


Home Learning

  • Complete worksheet on Redox and Oxidation States


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