14.1-The Reactivity Series

Reactivity Series

• Metal elements have either 1,2 or 3 electrons in their outer electron orbits.

  • This means that when they react they tend to lose electrons to form ionic compounds.

  • Metal ions are positively charged as they lose negative electrons.

• Some metals give up their electrons more readily than others and are, therefore, more reactive. Metals can be ranked according to their level of reactivity to form the metal reactivity series.

• Metals readily react with water and dilute acids, during these reactions hydrogen gas is given off.

• By comparing the rate at which each metal reacts with water and/or a dilute acid the metals can be placed in order to form the reactivity series.

• Metals at the top of the series tend to form ions more rapidly than those at the bottom.

  • Gold, for example, can be found in nature as gold metal in rocks as it does not react readily. Others like copper etc. are found as copper ore, copper compounds.

  • These have to undergo chemical processes to extract the pure metal from the ore.

• The non-metal elements hydrogen and carbon have been included in the reactivity series as they are often used with metals in experiments and they are also used to help extract metals from their naturally occurring metal ores.

Displacement Reactions

• Due to the relative reactivity of metals, given in the reactivity series, when combined they compete to form ionic compounds with other chemicals.

• More reactive metals will displace (push out) less reactive metals from metal salt compounds.

• This results in a new salt being formed and the weaker metal coming out of solution and being deposited as a metal precipitate.

• Magnesium ribbon placed into copper sulfate solution will result in the formation of a magnesium sulfate solution and the depositing of copper metal.

• The magnesium displaces the copper as it is a more reactive metal.

• Magnesium + Copper sulfate → Magnesium sulfate + Copper

14.2-Separating Metals from Metal Oxides

Metals react with oxygen in the air to produce metal oxides

• Oxidation and reduction involve the addition or removal of oxygen from a substance and are called redox reactions

• Oxidation is a reaction in which:

  • Oxygen is added to an element or a compound

• Reduction is a reaction in which:

  • Oxygen is removed from an element or a compound

• A common example is the reaction with red-brown copper metal to produce black copper oxide:

• 2Cu + O2 ⟶ 2CuO

• In this reaction copper metal has been oxidised since oxygen has been added to it

• Another example is the reaction of zinc oxide with carbon:

• ZnO + C ⟶ Zn + CO

• In this reaction the zinc oxide has been reduced since it has lost oxygen. The carbon atom has been oxidised since it has gained oxygen.

14.3-Redox Reactions

Oxidation and reduction

• Oxidation is the loss of electrons from a substance.

• It is also the gain of oxygen by a substance.

  • For example, magnesium is oxidised when it reacts with oxygen to form magnesium oxide:

    • magnesium + oxygen → magnesium oxide

    • 2Mg + O2 → 2MgO

• Reduction is the gain of electrons by a substance. It is also the loss of oxygen from a substance.

  • For example, copper(II) oxide can be reduced to form copper when it reacts with hydrogen:

  • copper(II) oxide + hydrogen → copper + water

  • CuO + H2 → Cu + H2O

• Usually, oxidation and reduction take place at the same time in a reaction. We call this type of reaction a redox reaction (red – reduction, ox – oxidation).

Note that:

• The oxidising agent is the chemical that causes oxidation by providing oxygen

• the reducing agent causes the other chemical to be reduced by removing oxygen

• Take a look at the following thermite reaction:

  • aluminium + iron(III) oxide → iron + aluminium oxide

  • 2Al + Fe2O3 → 2Fe + Al2O3

• Aluminium has been oxidised. This means that the iron(III) oxide is the oxidising agent.

• We can also see that the iron(III) oxide has been reduced.

• This means that the aluminium is the reducing agent.

Practice Questions

• What would you expect to see if zinc metal was placed in to copper sulphate solution?

  • Grey metal turns brown/brown metal displaced

  • Blue solution turns colourless

• And what are the products?

  • Copper and zinc sulphate

• Complete the following equations to show what happens when metals are heated with oxides of other metals:

  • magnesium + copper oxide

    • magnesium oxide + copper

  • lead+tin oxide

    • no reaction