Reactions of Metals (SQA National 5 Chemistry): Revision Note

Metal reactivity series

• Some metals, like potassium, are extremely reactive, while others, like gold, are very unreactive

• By comparing how vigorously different metals react, we can arrange them in order of their reactivity

  • This ordered list is called the reactivity series

• For National 5 Chemistry, the official version of this is the Electrochemical Series

  • This can be found on page 10 of the SQA Data Booklet

  • Metals higher up the series are more reactive

Building a simple reactivity series

• In the lab, a simple reactivity series can be built by comparing the the rate (speed) of reaction for different metals with the same substance, such as dilute acid

• Method:

  • Add small, equal-sized pieces of different metals to separate test tubes containing the same dilute acid

• The reaction produces hydrogen gas, which is observed as fizzing (effervescence)

• Observation:

  • The speed of the fizzing indicates the reactivity

  • The faster the fizzing, the more reactive the metal

• From these observations, we can create a simple reactivity series for these four metals:

most reactive > least reactive

magnesium > zinc > iron > copper

• This order matches their positions in the full Electrochemical Series

Metal reactions

• Reactive metals take part in chemical reactions where the metal atoms lose electrons (are oxidised) to form compounds

• For National 5 Chemistry, you need to know the general word equations for the reactions of metals with:

  1. Oxygen

  2. Water

  3. Dilute acids

Reaction with oxygen

• This reaction happens when a metal is burned in air or oxygen.

• The product is a metal oxide

• The general word equation is:

metal + oxygen → metal oxide

Reaction with water

• Only the most reactive metals will react with cold water

  • These include the alkali metals like lithium, sodium and potassium

• The products are a metal hydroxide and hydrogen gas

• The general word equation is:

metal + water → metal hydroxide + hydrogen

Reaction with acid

• Metals that are above hydrogen in the Electrochemical Series will react with dilute acids

• The products are a salt and hydrogen gas

• The general word equation is:

metal + acid → salt + hydrogen

Using metals to make soluble salts

• This method is used to make a soluble salt from the reaction of a moderately reactive metal and a dilute acid

• Suitable metals are:

  • Above hydrogen in the Electrochemical Series

  • But, not so reactive that the reaction is dangerous

  • For example, metals like magnesium, zinc or iron).

• Unreactive metals like copper (below hydrogen) will not react

The "excess" method

• This practical procedure is another example of the "excess method"

• The principle is to add more solid reactant (the metal) than is needed

  • This ensures that all of the acid is completely used up

  • This also stops the final salt being impure because it is contaminated with unreacted acid

• Any leftover solid can be easily removed by filtration

The method in brief

1. React

   • Add the metal in excess to a warm dilute acid

   • The reaction is complete when the fizzing stops and there is unreacted metal left over

2. Filter

   • Filter the mixture to remove the unreacted excess metal

   • The liquid that passes through is the pure salt solution (filtrate)

3. Crystallise

   • Gently evaporate the water from the filtrate and allow pure salt crystals to form

• This is the same practical procedure as preparing a salt from an insoluble oxide or carbonate

  • For a full step-by-step guide and diagrams, see the Preparation of Soluble Salts From Metal Oxides or Carbonates revision note