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Introduction

The production of iron in a blast furnace is an important industrial process, although other methods for iron production are also in use.

The basic idea involves the heating of an iron oxide, often haematite, Fe2O3, with carbon. A jet of air is used to burn the carbon to form the gas carbon dioxide. The carbon dioxide then reacts with more carbon to form carbon monoxide. Carbon monoxide is then used to reduce the iron oxide to iron. Carbon dioxide is also formed in this reaction. A diagram of the furnace is shown below.


Blast furnace

Task 1: The Blast Furnace


Model 1

  1. Open Yenka file Model 1. This scene demonstrates the chemistry of zone 1. Transfer the carbon to the gas tube and add the calcium hydroxide solution ('limewater') to the test tube. Turn on the Bunsen burner. Watch the temperature in the reaction details. When the temperature reaches about 400 °C, turn on the oxygen fully. Observe the changes in the percentage of oxygen in the gas and test tubes. What do you see happening in each tube when the temperature reaches about 800 °C?
    Answer
    The carbon begins to burn, and the limewater turns cloudy.
  2. What do we learn from the change to the limewater?
    Answer
    We learn that carbon dioxide gas has formed.
  3. (a) Write a balanced equation for the reaction that occurred in the gas tube.
    (b) Write a balanced equation for the reaction that took place in the test tube. (Note that lime water is
    Ca(OH)2 and the cloudiness that forms is a precipitate of calcium carbonate.)
    Answer
    (a) C + O2 → CO2
    (b) Ca(OH)2 + CO2 → CaCO3 + H2O
  4. Now open Scene 2 of the model. This scene attempts to show the chemistry of zone 2. Transfer the carbon to the gas tube and turn on the Bunsen burner and the carbon dioxide. Allow the temperature to rise to its maximum, which is over 800 °C. You will find that no reaction takes place. The reason for this is that a very high temperature is needed to make carbon react with carbon dioxide to form carbon monoxide. The temperature in zone 2 of the blast furnace is much higher than 800 °C. However, write a balanced equation for the reaction of carbon with carbon dioxide to form carbon monoxide.
    Answer
    C + CO2 → 2CO
  5. Open Scene 3 of the model. This shows the chemistry of zone 3. Transfer the iron oxide to the gas tube and turn on the carbon monoxide and the Bunsen burner. Watch the reaction details. What do you observe as the temperature rises to about 200 °C?
    Answer
    A reaction starts. Iron oxide is being converted to iron, and carbon dioxide is forming.
  6. Write a balanced equation for the reaction.
    Answer
    Fe2O3 + 3CO → 2Fe + 3CO2
  7. Since this reaction involves iron oxide being converted to iron metal, what type of reaction is involved?
    Answer
    Iron oxide contains iron in the form of iron ions, Fe​​3+
    These ions are converted to iron atoms, Fe. For this to happen, the Fe​​3+ ions must gain electrons. This is reduction.
  8. Another reaction that takes place in the blast furnace is the reduction of iron oxide to iron by carbon, the element. Write a balanced equation for this reaction.
    Answer
    2Fe2O3 + 3C → 4Fe + 3CO2

Summary

In a blast furnace, the reduction of iron takes place in three main stages:
Carbon combines with oxygen to form carbon dioxide:

C + O2 → CO2

Carbon dioxide reacts with carbon to form carbon monoxide:
CO2 + C → 2CO

Carbon monoxide reduces iron oxide to iron and carbon dioxide:
Fe2O3 + 3CO → 2Fe + 3CO2

Teacher Summary

  • Students should have some familiarity with the writing of balanced equations before undertaking this activity and the meaning of the term 'reduction' should be understood. This activity would fit into a topic on the extraction of metals or a topic on the chemical industry.