CIE iGCSE Co-ordinated Sciences-C6.3 Redox- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C6.3 Redox – Study Notes
CIE iGCSE Co-ordinated Sciences-C6.3 Redox – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Redox Reactions
Redox reactions are chemical reactions in which oxidation and reduction occur simultaneously. These reactions involve the transfer of electrons or oxygen between species.
- Oxidation: The gain of oxygen by a substance. It can also be described as the loss of electrons in other contexts.
- Reduction: The loss of oxygen by a substance. It can also be described as the gain of electrons in other contexts.
In a redox reaction:
- One substance is oxidized (gains oxygen).
- Another substance is reduced (loses oxygen).
Example
Classify the following reaction as a redox reaction and identify what is oxidized and what is reduced:
\( 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \)
▶️ Answer/Explanation
- Magnesium reacts with oxygen to form magnesium oxide.
- Magnesium gains oxygen → is oxidized.
- Oxygen is combined with magnesium → is reduced (loses its elemental form).
- Since both oxidation and reduction occur simultaneously, this is a redox reaction.
Redox Reactions (Oxygen Perspective)
Redox reactions can also be understood in terms of the gain and loss of oxygen:
- Oxidation: Gain of oxygen by a substance.
- Reduction: Loss of oxygen by a substance.
In any redox reaction, oxidation and reduction occur simultaneously. One substance gains oxygen (is oxidized) while another loses oxygen (is reduced).
Example
Identify the oxidation and reduction in the reaction:
\( \text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O} \)
▶️ Answer/Explanation
- Copper(II) oxide (\( \text{CuO} \)) loses oxygen → is reduced → forms copper (\( \text{Cu} \)).
- Hydrogen (\( \text{H}_2 \)) gains oxygen → is oxidized → forms water (\( \text{H}_2\text{O} \)).
- Both oxidation and reduction occur simultaneously → reaction is a redox reaction.
Oxidation and Reduction in Terms of Oxidation Numbers
Redox reactions can also be identified using oxidation numbers. An oxidation number shows the charge of an ion, and it helps us track electron transfer in a reaction.
- Oxidation: Increase in oxidation number (loss of electrons).
- Reduction: Decrease in oxidation number (gain of electrons).
At the IGCSE level, oxidation numbers are mainly used to name ions such as iron(II), iron(III), copper(II), etc., and to identify changes in reactions.
Example
In the reaction:
\( \text{Fe}^{2+} \rightarrow \text{Fe}^{3+} + e^- \)
Identify what happens to iron.
▶️ Answer/Explanation
- Iron changes from \( \text{Fe}^{2+} \) to \( \text{Fe}^{3+} \).
- Oxidation number increases from +2 to +3.
- This means iron has lost an electron → iron is oxidized.
Example
In the reaction:
\( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \)
Identify what happens to copper.
▶️ Answer/Explanation
- Copper changes from \( \text{Cu}^{2+} \) to \( \text{Cu} \).
- Oxidation number decreases from +2 to 0.
- This means copper has gained electrons → copper is reduced.
Oxidation
Oxidation can be defined in two complementary ways. Both definitions are used to identify which species is oxidized in a chemical reaction:
(a) Oxidation as loss of electrons:
Oxidation occurs when an atom, ion, or molecule loses one or more electrons during a chemical reaction.
- Example: \( \text{Na} \rightarrow \text{Na}^+ + e^- \)
- Here, sodium loses an electron → sodium is oxidized.
(b) Oxidation as an increase in oxidation number:
Oxidation can also be described as an increase in the oxidation state (number) of an element in a compound or ion.
- Example: \( \text{Fe}^{2+} \rightarrow \text{Fe}^{3+} + e^- \)
- Oxidation number of iron increases from +2 to +3 → iron is oxidized.
Key Points:
- Oxidation always involves a transfer of electrons in some form.
- It can be identified either by actual electron loss or by observing an increase in oxidation number.
- In redox reactions, oxidation always occurs simultaneously with reduction.
Example
Identify the species being oxidized in the reaction:
\( \text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \)
▶️ Answer/Explanation
- Magnesium reacts with oxygen to form magnesium oxide.
- Magnesium loses electrons to oxygen → magnesium is oxidized.
- Oxidation number of magnesium increases from 0 to +2.
- Oxygen gains electrons (reduction) simultaneously → this is a redox reaction.
Reduction
Reduction can be defined in two complementary ways. Both definitions help identify which species is reduced in a chemical reaction:
(a) Reduction as gain of electrons:
Reduction occurs when an atom, ion, or molecule gains one or more electrons during a chemical reaction.
- Example: \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \)
- Copper ion gains two electrons → copper is reduced.
(b) Reduction as a decrease in oxidation number:
Reduction can also be described as a decrease in the oxidation state (number) of an element in a compound or ion.
- Example: \( \text{Fe}^{3+} + e^- \rightarrow \text{Fe}^{2+} \)
- Oxidation number of iron decreases from +3 to +2 → iron is reduced.
Key Points:
- Reduction always involves a transfer of electrons in some form.
- It can be identified either by actual electron gain or by observing a decrease in oxidation number.
- In redox reactions, reduction always occurs simultaneously with oxidation.
Example
Identify the species being reduced in the reaction:
\( \text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O} \)
▶️ Answer/Explanation
- Copper(II) oxide loses oxygen → forms copper metal.
- Copper gains electrons during the reaction → copper is reduced.
- Hydrogen loses electrons → oxidized to water.
- Both oxidation and reduction occur simultaneously → redox reaction.