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Displacement Reactions

Some Standard Reduction Potentials

Oxidants

 

Reductants

E0
(volts)

Weakest
Oxidant
K++e K(s) -2.94 Strongest
Reductant
Ba2++2e Ba(s) -2.91
Ca2++2e Ca(s) -2.87
Na++e Na(s) -2.71
Mg2++2e Mg(s) -2.36
Al3++3e Al(s) -1.68
Mn2++2e Mn(s) -1.18
Zn2++2e Zn(s) -0.76
Fe2++2e Fe(s) -0.44
Ni2++2e Ni(s) -0.24
Sn2++2e Sn(s) -0.14
Pb2++2e Pb(s) -0.13
Cu2++2e Cu(s) 0.34
Strongest
Oxidant
Ag++e Ag(s) 0.80 Weakest
Reductant

Key Concepts

A more active metal will displace a less active metal from solution.
  • A more active metal

    (i) loses electrons more easily

    (ii) is the stronger reductant

    (iii) is the weaker oxidant

    (iv) has a lower standard reduction potential

  • The less active metal

    (i) is less likely lose electrons

    (ii) is the weaker reductant

    (iii) is the stronger oxidant

    (iv) has a higher standard reduction potential

An activity series places metals in order from most active to least active.

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  • An activity series lists metals in order of decreasing strength as reductants

        Based on the Standard Reduction Potentials above, an activity series would be:

    most active metalsleast active metals
    metalsK > Ba > Ca > Na > Mg > Al > Mn > Zn > Fe > Ni > Sn > Pb > Cu > Ag
    Eo-2.94-2.91 -2.87-2.71-2.36-1.68-1.18-0.76-0.44-0.24-0.14-0.13+0.34+0.80
    lowest Eohighest Eo
    easiest to oxidizehardest to oxidize
    strongest reductantsweakest reductants
    M → M+ + e- likelyM+ + e- → M likely

    In this series the most active metal is potassium (K) and the least active metal is silver (Ag)

Example Using the Activity Series

If a clean strip of copper were placed in a 1M zinc nitrate solution, would the copper displace the zinc from solution?

  1. Use the activity series above to decide which metal is the more active:

    Zn is more active than Cu

  2. Decide whether copper will displace zinc from solution:

    A more active metal displaces a less active metal from solution:

    Zinc is a more active metal than copper.

    So, copper will not displace zinc from the solution.

Example Using Standard Reduction Potentials

If a strip of clean magnesium metal were placed in a 1M copper sulphate solution, would the magnesium metal displace the copper from solution?
  1. Write the reduction equations for the reactions being considered:

    magnesium : Mg2+ + 2e- → Mg
    copper : Cu2+ + 2e- → Cu

  2. Use a table of standard reduction potentials to find the Eo value for each reaction:

    magnesium : Mg2+ + 2e- → Mg Eo = -2.36 V
    copper : Cu2+ + 2e- → Cu Eo = +0.34 V

  3. Decide which metal is the stronger reductant:

    Eo for the magnesium reaction is less than Eo for the copper reaction.

    Magnesium is a stronger reductant than copper.

  4. Decide whether magnesium will displace copper ions in the solution:

    A stronger reductant displaces a weaker reductant from solution.

    Magnesium will displace copper from the solution: Mg(s) → Mg2+(aq) + 2e- will occur.

    This means that solid copper will form: Cu2+(aq) + 2e- → Cu(s) will occur.


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