You will find out: Show > what makes iron rust and some ways to stop it > what a redox reaction is > why rusting is a redox reaction Rusting iron When metals corrode they are taking part in a redox reaction. Rusting iron is just one example of this. Redox is a word made up from two processes that work together. The two processes are oxidation and reduction. Oxidation is the addition of oxygen to a substance. Reduction is the removal of oxygen from a substance.  Figure 1: What is needed for objects to rust? Iron and steel only rust when oxygen (in the air) and water are touching their surfaces. > Iron needs oxygen to rust. > Iron needs water to rust. Rust is not just iron oxide. Its scientific name is: hydrated iron(III) oxide The 'hydrated' part tells us that water is needed as well as oxygen. Figure 2: The Titanic sank almost 100 years ago. Why is it rusting only slowly? Six ways of preventing rust
Figure 3: Six ways to prevent rust. To stop iron from rusting, just remove either water or oxygen: > stop water touching the iron – iron does not rust in air if the air is very dry > stop oxygen from touching the iron. Covering the iron with a layer of oil, grease or paint stops the iron rusting for both of these reasons. If a ship sinks to the bottom of the sea, air can still get to it because air dissolves in water. As both water and air are touching the ship, the ship rusts. If the water is deep there is very little dissolved air. The Titanic sank in water 2.5 miles deep, so it is rusting very slowly. Questions 1. What is the chemical name for rust? 2. State two things needed for iron to rust. 3. Name five ways to prevent iron from rusting. 4. Suggest why painting the chain in Figure 3 above does not stop it rusting for long. Rusting is a redox reaction. In a redox reaction, both reduction and oxidation take place. iron + oxygen + water → hydrated iron(III) oxide How to prevent iron from rusting by galvanising Galvanising protects iron from rusting when it is covered by a layer of zinc. The layer of zinc stops water and oxygen from reaching the surface of the iron. It also acts as a sacrificial metal. This means that it reacts with the water or oxygen instead of the iron, as it is a more reactive metal. Only iron can rust. Most metals corrode, but when iron corrodes we give it a special name – rusting. Salt acts as a catalyst for rusting iron. Salt doesn't make iron rust in the first place. Questions 5. A car left in the Sahara desert does not rust as quickly as a car in the UK. Suggest why. 6. Explain why ships that sink in shallow water rust quite quickly. 7. What happens in a redox reaction? 8. Write a word equation for the rusting of iron. Oxidation and reduction can also be described in terms of electrons. A substance is oxidised if it loses electrons. An oxidising agent takes electrons away from a substance. A substance is reduced if it gains electrons. A reducing agent pushes electrons onto another substance so that it gains them. Rust and redox When iron rusts, the oxygen is the oxidising agent; it takes electrons from the iron. The electrons go onto the oxygen, so the oxygen itself has been reduced. > Iron loses electrons - it is oxidised. > Oxygen gains electrons - it is reduced. Reversing the reaction Redox reactions can be forced in either direction. One direction is oxidation; the other direction is reduction. > Iron is normally oxidised, but it can be pushed back (Figure 4). Figure 4: Oxidation/reduction of iron. > Iron ions can be forced from one type to another (Figure 5). Figure 5: Oxidation/reduction of iron ions. > Chlorine is like oxygen, it is normally reduced (Figure 6). Figure 6: Oxidation/reduction of chlorine. When these reactions take place, an electrode potential is set up. Each reaction at the electrode has a different electrode potential. These can be used in calculations. When a magnesium ion gains two electrons to become a magnesium atom, the voltage measured is −2.37 V. When a zinc ion gains two electrons to become a zinc atom, the voltage measured is −0.76 V. This is because zinc is a less reactive metal than magnesium. Questions 9. Chlorine accepts electrons. Is it an oxidising agent or a reducing agent? 10. Use the above equations to suggest what the '(III)' in iron(III) oxide tells you. 11. When sulfur reacts with hydrogen it gains electrons from hydrogen.
Why is rusting considered a redox reaction?Rust and redox
When iron rusts, the oxygen is the oxidising agent; it takes electrons from the iron. The electrons go onto the oxygen, so the oxygen itself has been reduced.
How does rusting of iron show that this is a redox reaction?Corrosion of metal is a redox reaction as the metal loses electrons to oxygen and water, which act as the oxidising agents to receive the electrons. Corrosion of iron is also called rusting. Rusting of iron can only occur if both oxygen and water are present.
Is rusting of iron a redox reaction Class 10?Rusting of iron refers to the formation of rust, a mixture of iron oxides, on the surface of iron objects or structures. This rust is formed from a redox reaction between oxygen and iron in an environment containing water (such as air containing high levels of moisture).
Why is the oxidation of iron a redox reaction?The oxygen has been reduced. The electrons from the iron went to the oxygen. Every oxidation process has to have a corresponding reduction. We call these redox reactions, the word redox combining reduction and oxidation.
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How is rusting of iron a redox reaction?
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