What happens when metals react with oxygen? In the previous chapter, students learned how to write and balance equations. In this chapter, they will learn about the reaction of metals with oxygen. While magnesium plus oxygen gives magnesium oxide, iron plus oxygen gives iron oxide, and copper plus oxygen gives copper oxide. If you burn metal in the air, it will start reacting with oxygen to form a metal oxide, which is basic in nature and turns red litmus to blue.

On the other hand, potassium and sodium are metals stored under kerosene oil to prevent them from reacting with oxygen, carbon dioxide, and moisture in the air. These two are so reactive that they can react vigorously with oxygen. If you keep them open in the air, they will catch fire and start burning. Read on to know more about the reactions of metals with oxygen.

The Reaction of Metals with Oxygen: What Are Metals?

Metals are the electropositive element. They donate electrons and form positive ions and then become stable. Check the example below.

Na → Na+ + e–

Metals have certain distinguishing physical properties. If you know these distinct physical properties, you can quickly identify and classify them.

Check out some main physical properties of metals.

• Metals have a lustre, and they have a metallic appearance.
• Metals are great conductors of heat and electricity.
• Metals are usually solid at room temperature.
• Metals have a very high melting point.
• Metals are ductile and malleable.

The Reaction of Metals with Oxygen Description

Students can observe metal’s reaction with oxygen in their day-to-day life. You must have observed silver jewellery getting tarnished, rusting of iron, or even copper articles are covered with a green layer. Metals react with atmospheric oxygen and produce metal oxides that are basic in nature, and that is because metals also react with water to form bases.

• If you observe rusting of iron, you will find the iron reacts with the oxygen in the air and moisture. After that, it develops rust that is hydrated iron (III) oxide.
• Let us look at how iron reacts with oxygen. You may use steel wool in some cases for these experiments. Before starting your experiment, you must know what steel wool is. Wire wool is made of very fine steel threads. It is known as steel wool. On the other hand, steel is an alloy that is made mostly of iron. So, you must have observed that when you look at the experiment of steel wool burning in oxygen, you are actually observing how iron reacts with oxygen.
• A solid mixture of two or more distinct metal elements is known as a metal alloy. Brass and steel are perfect examples of metal alloys.
• When a substance is burned in the air, the reaction is known as a combustion reaction. If a substance combusts in air, it actually reacts with oxygen.

 Iron Chain Left in Moist Air Got Rusted

• If you observe rusting of copper, the metallic copper actually reacts with atmospheric moisture, oxygen, and carbon dioxide. After that, it develops a green-coloured coating. That green-coloured coating is of copper carbonate and copper hydroxide.

2Cu+O2+H2O+CO2 ⟶Cu2(OH)2+CuCO3

Copper Develops Green-Coloured Rust on Exposure to Moist Air

• If you observe the tarnishing of silver articles, you will find the metallic silver reacts with hydrogen sulphide or sulphur present in the air. Then only it gets tarnished.

The General Reaction of Metals with Oxygen

Therefore, students can write a general word equation in which a metal reacts with oxygen. The general word equation is given below.

metal + oxygen → metal oxide

When words are used to describe a reaction, we still operate on the macroscopic level. 

The Chemical Equation

The reaction between oxygen and magnesium is translated into a chemical equation below.

2 Mg + O2→ 2 MgO

This is a symbolic representation as the chemical equation consists of symbols.

Remember that the metals in the same group will react similarly with oxygen. So, calcium reacts just like magnesium reacts with oxygen. The chemical equations will also show similarities. Check out the chemical equation for the reaction between oxygen and calcium below.

2Ca + O2→2CaO

The Reaction of Metals with Oxygen: What is Rust?

Students must have an idea about rust as well. When iron is exposed in the air to oxygen, a reaction starts occurring slowly. The iron reacts slowly with oxygen. As a result, it is gradually eaten away. Iron will rust more quickly if it is exposed to wet conditions.

A mixture of different oxides of iron is known as rust. The rusting of iron is an excellent example of the corrosion process.

Rusting happens much faster near the ocean. You must have understood why? That is because of water droplets with salt. It makes them even more corrosive. 

Apart from that, rusting happens quickly in the presence of acids. The air inside factories or laboratories is very corrosive because acids are used or stored there. We can identify an area with a corrosive climate where the air contains moisture mixed with salt and acid.

People who live near the ocean must make their window frames or doors with wood instead of steel or iron. That is because they are living in a corrosive climate. Wood never rusts. Many people also utilise aluminium as it does not rust as well.

Problems with Rust

• Rust is a natural process. But its effects are quite beautiful.
• Keep in mind that rust (iron oxide) and iron are two different materials. Therefore they have different properties.
• Iron can be strengthened and made more resistant to rust if you mix it with other elements, as it will be turned into steel.
•  People use steel in the construction of buildings. It is strong. But steel is not completely rust-resistant. But in corrosive or moist climates, it can be protected against rust.

How to Prevent Rust?

Rust can be formed on the surface of steel or iron when it comes into contact with oxygen. The oxygen molecules collide with the iron atoms, and they react to form iron oxide. Now the question is, what should we do to prevent this? 

• You can stop or slow down rust in several ways. Cover the surface of the iron with a metal that does not corrode. It can be chromium. The iron surface of taps and bathrooms is often covered by chromium to protect it from contact with the air.
• Paint is also a barrier to rust but not the ultimate barrier as if the surface is scratched, it will automatically peel off, and the metal will be exposed to the air.

In this chapter, we learned about the reaction of metals with oxygen. We also learned about metal oxide (iron oxide or rust), how it forms and how to prevent objects from rusting.

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