sci_chem
Redox Reactions
Chapter summary, hard words and model exam answers for ICSE Class 10 Hindi.
Free online summary and notes (ICSE Class 10 Hindi). Read it here, no PDF download needed.
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Chemistry · CBSE 10 · ICSE 10 · GCSE (AQA, Edexcel, OCR)
Summary
Redox is short for reduction-and-oxidation. The simplest definition uses oxygen: oxidation is gaining oxygen, reduction is losing it. When magnesium burns, 2Mg + O2 -> 2MgO, magnesium gains oxygen so it is oxidised. The stronger, modern definition uses electrons and works even when no oxygen is present.
Oxidation is the loss of electrons; reduction is the gain of electrons. They are two halves of one event: the electrons one atom loses are exactly the electrons another atom gains. In Zn + Cu2+ -> Zn2+ + Cu, zinc loses 2 electrons (oxidised) and the copper ion gains them (reduced).
The reducing agent is the electron donor; by giving electrons away it is itself oxidised. The oxidising agent is the electron acceptor; by taking electrons it is itself reduced. So zinc is the reducing agent and Cu2+ is the oxidising agent.
Rusting needs both air and water. Iron loses electrons to oxygen and slowly turns to hydrated iron(III) oxide (rust). It is stopped by painting, oiling, or galvanising (a sacrificial zinc coat).
Hard words & meanings
| oxidation | loss of electrons (or gain of oxygen / loss of hydrogen) by a species |
| reduction | gain of electrons (or loss of oxygen / gain of hydrogen) by a species |
| redox reaction | a reaction in which oxidation and reduction occur together |
| oxidising agent | a substance that takes electrons from another and is itself reduced |
| reducing agent | a substance that gives electrons to another and is itself oxidised |
| oxidation number | a value showing how many electrons an atom has effectively lost or gained |
| half-equation | an equation showing just the electrons lost or gained by one species |
| reactivity series | a list of metals in order of how readily they lose electrons |
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