Reactivity of Metals and Extraction
This section explains reactivity of metals and extraction, covering, reaction of metals with oxygen, the reactivity series, oxidation and reduction in terms of electrons and extraction of metals and reduction.
Reaction of Metals with Oxygen
When metals react with oxygen, they form metal oxides. This is a type of oxidation reaction where the metal gains oxygen. For example, copper reacts with oxygen to form copper oxide:
Example: Copper and Oxygen Reaction
$$2Cu + O_2 \rightarrow 2CuO$$
This reaction shows copper (Cu) combining with oxygen (O₂) to form copper(II) oxide (CuO), a black solid. The reaction involves the metal losing electrons to form a positive ion (oxidation).
The Reactivity Series
The reactivity series is a table that lists metals in order of their reactivity. The most reactive metals are at the top, and the least reactive metals are at the bottom. The series can help predict how metals will react with water and acids.
Reactivity Series Table:
| Metal | Reaction with Water | Reaction with Acid |
|---|---|---|
| Potassium (K) | Very vigorous, forming hydrogen gas and hydroxide | Reacts vigorously with dilute acids |
| Sodium (Na) | Vigorous, forming hydrogen gas and hydroxide | Reacts vigorously with dilute acids |
| Calcium (Ca) | Reacts slowly with cold water, more vigorously with hot water | Reacts with dilute acids |
| Magnesium (Mg) | Reacts slowly with cold water, more vigorously with hot water | Reacts with dilute acids |
| Aluminium (Al) | Reacts very slowly with water but the oxide layer can prevent further reaction | Reacts with dilute acids |
| Zinc (Zn) | Reacts slowly with acid | Reacts with dilute acids |
| Iron (Fe) | Reacts slowly with water | Reacts with dilute acids |
| Copper (Cu) | Does not react with water | Reacts very slowly with acids |
The reactivity of a metal determines its ability to displace other metals in a reaction and whether it will react with substances like water and acids.
Oxidation and Reduction in Terms of Electrons
Oxidation: Oxidation is the process where a substance loses electrons. In terms of metals, oxidation occurs when a metal reacts with oxygen to form a metal oxide. For example:
$$2Mg \rightarrow 2Mg^{2+} + 4e^-$$
Here, magnesium (Mg) loses two electrons to form magnesium ions (Mg²⁺). The metal is oxidised.
Reduction: Reduction is the process where a substance gains electrons. In the context of metal extraction, a metal ion gains electrons to become a metal. For example, in the extraction of copper from copper(II) oxide:
$$CuO + H_2 \rightarrow Cu + H_2O$$
Here, copper(II) oxide (CuO) is reduced because the copper ions (Cu²⁺) gain electrons to form copper metal (Cu).
In a reaction, one substance undergoes oxidation (loses electrons) while another undergoes reduction (gains electrons). This is known as a redox reaction.
Extraction of Metals and Reduction
The extraction of metals involves removing them from their ores, often by reducing metal oxides. The method of extraction depends on the metal's position in the reactivity series:
For highly reactive metals (e.g. sodium, potassium), electrolysis is used to extract the metal. This process involves passing an electric current through a molten metal oxide to break it down into its components.
For less reactive metals (e.g. copper, gold), the metal can often be extracted by heating the metal oxide with a more reactive substance, such as carbon. For example:
$$CuO + C \rightarrow Cu + CO_2$$
Here, carbon is used to reduce copper(II) oxide to copper metal, and carbon dioxide (CO₂) is released.
For very unreactive metals (e.g. gold), they can often be found in their native state and do not require reduction as they are already pure metal.
By using the process of reduction, metals are extracted from their ores, which involves the metal ions gaining electrons to form pure metal atoms.
This guide covers the fundamental ideas about the reactivity of metals, their reactions with oxygen, and the process of metal extraction. Understanding these concepts is essential for mastering the topic of chemical and energy changes in GCSE Chemistry.
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