Displacement Reactions of Metals (1) - Activity

Introduction

Apart from the reactions of metals with oxygen, water and acid, the metal Reactivity Series can also be obtained by reacting a metal with a compound of another metal. In fact, this is the most reliable way to establish the order of reactivity. It is not necessary to observe the speed of the reaction. In mixing one metal with a compound of another to see if a displacement reaction happens, there is either a reaction or there isn't! If a reaction occurs, one metal will displace the other metal from its compound. Here you will look at using the displacement rule.

Task 1: Using the displacement rule


Model

  1. Open the Yenka Model 1 and look at what happens when metals are added to salt solutions of other metals.
    (a) From the results, give the reactivity order of copper, gold, iron, silver and zinc (with the most reactive metal first).
    (b) Describe what you might observe if (i) zinc is added to copper nitrate equation (at least two main observations), (ii) silver is added to iron sulfate solution and (iii) copper is added to platinum chloride solution (it is observed that platinum tarnishes less than copper when used in jewellery).
    (c) Write a word equation for any reaction that might take place or explain why one doesn't take place.
    Answer
    (a) Zinc; iron; copper; silver; gold
    (b) (i) orange-brown coating of copper on the zinc; blue colour fades, eventually becoming colourless; zinc dissolves, solution warms up; (ii) no change, (iii) copper becomes silvery coated in platinum; solution turns green-blue as copper dissolves
    (c) (i) zinc + copper nitrate → copper + zinc nitrate (ii) No reaction because silver is less reactive than iron. (iii) the lack of tarnishing by platinum suggests it is less reactive than copper, so copper will displace platinum: copper + platinum chloride → platinum + copper chloride
  2. Open Yenka file Model 2.
  3. Investigate the reaction of Fe (iron) with CuO, ZnO and MgO (copper, zinc and magnesium oxides respectively). Place the iron in the dish with each of the chemicals in turn and turn up the heat. Once you have completed one reaction, reload the model (by pressing F5) before attempting the next. Now repeat for Cu (copper) with FeO, ZnO and MgO and Mg (magnesium) with CuO, ZnO or FeO.
  4. What is the general rule in deciding whether a reaction will take place?
    Answer
    The more reactive metal will displace a less reactive metal from its compounds.
  5. Complete the following word equations with either the products or the statement, NO reaction. It would be a good idea to write out the reactivity order of the four metals concerned.
    (a) Copper + iron oxide → ?
    (b) Magnesium + zinc oxide → ?
    (c) Copper + magnesium oxide → ?
    (d) Iron + magnesium oxide → ?
    (e) Zinc + copper oxide → ?
    (f) Magnesium + iron oxide → ?
    (g) Copper + iron oxide → ?
    (h) Zinc + iron oxide → ?
    (i) Copper + zinc oxide → ?
    (j) Iron + zinc oxide → ?
    (k) Magnesium + zinc oxide → ?
    Answer
    (a) NO reaction, (b) magnesium oxide + zinc, (c) NO reaction, (d) NO reaction, (e) zinc oxide + copper, (f) magnesium oxide + iron, (g) NO reaction, (h) zinc oxide + iron, (i) NO reaction, (j) NO reaction, (k) magnesium oxide + zinc
  6. (a) Do displacement reactions give out heat? What do we call a reaction that gives out heat?
    (b) Which of the reactions in Task 2 would be the most dangerous and why? Give a reason for your choice of answer.
    (c) What might you observe if a reaction takes place?
    (d) What safety precautions would you take when carrying out the experiment?
    Answer
    (a) Yes, displacement reactions give out heat: exothermic.
    (b) The bigger the difference in reactivity between the added metal and the metal in the compound, the more vigorous the reaction (more exothermic). So the fastest/most vigorous, and therefore the most dangerous, would be: magnesium + copper oxide → magnesium oxide + copper.
    (c) Glows red at least, possibly sparks.
    (d) Wear safety glasses and carry it out behind a safety screen.

Summary

A more reactive metal will displace a less reactive metal from its compounds.
This means you can predict the outcome of trying to react a metal with the compound of another metal and you can also make a reasonable prediction of what you might see.
It does not matter whether the compound of the less reactive metal is, e.g., a solid oxide or a salt solution, a reaction should take place, even if heat is needed to get it going!

Teacher Summary

  • None