Electron Loss and Gain

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Redox Chemistry

Last updated 2:13 PM on 8/30/26
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46 Terms

1
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What is oxidation in terms of electrons?
Oxidation is the loss of electrons.
2
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What is reduction in terms of electrons?
Reduction is the gain of electrons.
3
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What mnemonic can be used to remember oxidation and reduction?
OIL RIG: Oxidation Is Loss, Reduction Is Gain.
4
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What is a redox reaction?
A reaction in which oxidation and reduction occur at the same time.
5
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How was oxidation originally defined?
The addition of oxygen.
6
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How was reduction originally defined?
The removal of oxygen.
7
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How can oxidation also be described in terms of hydrogen?
The removal of hydrogen.
8
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How can reduction also be described in terms of hydrogen?
The addition of hydrogen.
9
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What happens to magnesium when it burns in oxygen?
Magnesium is oxidised because it loses electrons to form Mg²⁺ ions.
10
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What is the equation for the oxidation of magnesium atoms?
Mg → Mg²⁺ + 2e⁻.
11
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What happens to oxygen when magnesium burns in oxygen?
Oxygen is reduced because it gains electrons to form oxide ions.
12
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What is the half-equation for the reduction of oxygen?
O₂ + 4e⁻ → 2O²⁻.
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Why is magnesium oxidised in the reaction 2Mg + O₂ → 2MgO?
Each magnesium atom loses two electrons.
14
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Why is oxygen reduced in the reaction 2Mg + O₂ → 2MgO?
The oxygen molecule gains four electrons overall.
15
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What is oxidation in terms of oxidation number?
Oxidation is an increase in oxidation number.
16
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What is reduction in terms of oxidation number?
Reduction is a decrease in oxidation number.
17
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What is an oxidising agent?
A species that oxidises another species by removing one or more electrons from it.
18
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What happens to an oxidising agent during a reaction?
It gains electrons and is therefore reduced.
19
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What is a reducing agent?
A species that reduces another species by donating one or more electrons to it.
20
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What happens to a reducing agent during a reaction?
It loses electrons and is therefore oxidised.
21
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In the reaction between magnesium and oxygen, what is the oxidising agent?
Oxygen, because it gains electrons and causes magnesium to be oxidised.
22
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In the reaction between magnesium and oxygen, what is the reducing agent?
Magnesium, because it loses electrons and causes oxygen to be reduced.
23
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What important exam rule should you remember about an oxidising agent?
An oxidising agent is itself reduced.
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What important exam rule should you remember about a reducing agent?
A reducing agent is itself oxidised.
25
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What is a disproportionation reaction?
A reaction in which the same element in a single species is simultaneously oxidised and reduced.
26
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What happens in the disproportionation reaction Cu₂O + H₂SO₄ → CuSO₄ + Cu + H₂O?
Copper(I) ions are both oxidised to Cu²⁺ and reduced to Cu.
27
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Why is the reaction involving copper(I) oxide and sulfuric acid a disproportionation reaction?
The same element, copper, undergoes both oxidation and reduction.
28
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In Cu₂O, what happens to one Cu⁺ ion during disproportionation?
It loses an electron and is oxidised to Cu²⁺.
29
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In Cu₂O, what happens to another Cu⁺ ion during disproportionation?
It gains an electron and is reduced to Cu.
30
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What is meant by electron transfer in a redox reaction?
Electrons are transferred from the species being oxidised to the species being reduced.
31
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In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, which species is oxidised?
Zinc is oxidised.
32
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In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, which species is reduced?
Cu²⁺ ions are reduced.
33
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What is the oxidation half-equation for zinc in Zn + Cu²⁺ → Zn²⁺ + Cu?
Zn → Zn²⁺ + 2e⁻.
34
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What is the reduction half-equation for copper(II) ions?
Cu²⁺ + 2e⁻ → Cu.
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Why is zinc the reducing agent in Zn + Cu²⁺ → Zn²⁺ + Cu?
Zinc loses electrons, causing Cu²⁺ ions to gain electrons and be reduced.
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Why are Cu²⁺ ions the oxidising agent in Zn + Cu²⁺ → Zn²⁺ + Cu?
Cu²⁺ ions gain electrons and cause zinc to lose electrons.
37
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How can you identify oxidation using oxidation numbers?
The oxidation number of an element increases.
38
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How can you identify reduction using oxidation numbers?
The oxidation number of an element decreases.
39
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If a species loses electrons, what happens to its oxidation number?
It increases.
40
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If a species gains electrons, what happens to its oxidation number?
It decreases.
41
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What does a half-equation show?
It shows either the oxidation or reduction process, including the electrons transferred.
42
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Where are electrons written in an oxidation half-equation?
On the product side because electrons are lost.
43
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Where are electrons written in a reduction half-equation?
On the reactant side because electrons are gained.
44
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How can you check that a half-equation is balanced?
The number of atoms and the overall charge must be the same on both sides.
45
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In a redox reaction, must oxidation and reduction always happen together?
Yes, because electrons lost by one species must be gained by another.
46
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What is meant by simultaneous oxidation and reduction?
One species loses electrons while another gains electrons during the same reaction.