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Redox reaction in the displacement of metals from its salt solution

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Redox reaction in the displacement of metals from its salt solution

  • Generally, metals are good electron donors and therefore are good reducing agents. However, different metals have different strength as reducing agents.
  • The strength of metals as reducing agents can be compared by using the electrochemical series.
  • The electrochemical series lists metals according to their electropositivity, that is, according to their ability to lose electrons to form positive ions.
    Redox reaction in the displacement of metals from its salt solution 1
  • The higher the position of a metal in the electrochemical series, the more electropositive the metal is, the easier it is for the metal to lose its electrons. Thus, the better reducing agent the metal is.
  • On the other hand, the ability of a metal ion to accept electrons increases down the series. Thus, the strength of a metal ion as an oxidising agent increases down the electrochemical series.
  • In a displacement of metal, a more electropositive metal will displace a less electropositive metal from its salt solution.
    (a) The more electropositive metal acts as the reducing agent. It loses electrons and undergoes oxidation to form positive ions.
    (b) The ions of the less electropositive metal act as an oxidising agent by accepting the electrons. While doing so, the ions are reduced to metallic atoms.
    (c) In short, there is an electron transfer from the more electropositive metal to the ions of the less electropositive metal.

 

Oxidation and reduction in the displacement of metals experiment

Aim: To investigate oxidation and reduction in the displacement of metals.
Materials: Zinc strip, copper strip, 0.5 mol dm-3 copper(II) sulphate solution, 0.1 mol dm-3 silver nitrate solution, sandpaper.
Apparatus: Test tubes, test tube rack.
Procedure:

  1. 2 cm3 of 0.5 mol dm-3 copper(II) sulphate solution and 2 cm3 of 0.1 mol dm-3 silver nitrate solution are poured into two separate test tubes.
  2. A strip of zinc and a strip of copper are cleaned with sandpaper. The strips are then dropped into the test tubes as shown in Figure.
    Redox reaction in the displacement of metals from its salt solution 2
  3. Any change in colour and whether any metal is deposited are observed.

Observations:

Test tubeObservations
X
  • The blue colour of the solution slowly fades until it becomes colourless.
  • The zinc strip dissolves.
  • A brown solid is deposited.
Y
  • The colourless solution slowly turns blue.
  • The copper strip dissolves.
  • A silvery grey solid is deposited.

Discussion:

  1. In test tube X, zinc displaces copper from its salt solution.
    (a) Zinc is more electropositive than copper. Thus, zinc acts as the reducing agent, losing electrons to form zinc ions. By doing so, zinc is oxidised. This explains why the zinc strip dissolves.
    Redox reaction in the displacement of metals from its salt solution 3
    (b) The electrons are accepted by copper(II) ions in the solution. Thus, copper(II) ions act as the oxidising agent and are reduced to metallic copper. The brown solid deposited in test tube X is copper metal.
    Redox reaction in the displacement of metals from its salt solution 4
    (c) The decreasing amount of copper(II) ions in the solution causes the solution to slowly change colour from blue to colourless.
    (d) The redox reaction that occurs can be represented by the following equation.
    Redox reaction in the displacement of metals from its salt solution 5
  2. In test tube Y, copper displaces silver from its salt solution.
    (a) Copper is more electropositive than silver. So, copper acts as the reducing agent, losing electrons to form copper(II) ions. In other words, copper is oxidised. This explains why the copper strip dissolves.
    Redox reaction in the displacement of metals from its salt solution 6
    (b) The increasing amount of copper(II) ions in the solution causes the solution to slowly change colour from colourless to blue.
    Redox reaction in the displacement of metals from its salt solution 7
    (c) The electrons are accepted by silver ions in the solution. Thus, silver ions act as the oxidising agent and are reduced to silvery grey silver.
    (d) The redox reaction that occurs can be represented by the following equation.
    Redox reaction in the displacement of metals from its salt solution 8

Conclusion:
A more electropositive metal can displace a less electropositive metal from its salt solution whereby the more electropositive metal acts as the reducing agent and the ions of the less electropositive metal act as the oxidising agent.

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