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Chemistry IGCSE > Redox Reactions > Flashcards

Redox Reactions Flashcards

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1
Q

Oxidation

A

A reaction where a substance gains oxygen

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2
Q

What is the mnemonic for oxidation?

A

OIL RIG
Oxidation
Is
Loss of electrons
Reduction
Is
Gain of electrons

Oxidizing agent
Is
Losing Oxygen
Reducing agent
Is
Gaining oxygen

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3
Q

What does the term “redox” stand for?

A

Redox stands for reduction and oxidation reactions occurring simultaneously.

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4
Q

Reduction

A

Reduction is a reaction where a substance loses oxygen.

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5
Q

Reducing agent

A

A reducing agent is a substance that takes oxygen away from another chemical.

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6
Q

Oxidizing agent

A

An oxidizing agent is a substance that provides oxygen to another chemical.

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7
Q

In the reaction between magnesium and carbon dioxide, what happens to carbon and magnesium?

A

Carbon is reduced as it loses oxygen, while magnesium is oxidized as it gains oxygen.

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8
Q

Name two types of reactions that are not considered redox reactions.

A

Neutralization and precipitation reactions.

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9
Q

What is the primary method for extracting metals from their ores?

A

The primary method is reduction using a reducing agent, often carbon.

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10
Q

Why are most metals found as compounds in nature?

A

Most metals react with oxygen over time, forming compounds such as oxides.

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11
Q

Give an example of a metal that can be found in its elemental form.

A

Silver or gold can be found in their elemental forms.

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12
Q

What is an ore?

A

An ore is a naturally occurring compound from which metals can be extracted back into their elemental form.

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13
Q

What is the most common reducing agent used in the extraction of metals?

A

Carbon, because it acts as a reducing agent. The Carbon is more reactive than the lead.

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14
Q

Why is carbon a good reducing agent for the extraction of metals?

A
  • It is common
  • It produces CO2 which is a gas and leaves us with the pure metallic element
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15
Q

What determines the method of extraction for different metals?

A

The reactivity series of metals determines the method of extraction.

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16
Q

What is a mnemonic to remember the reactivity series of metals?

A

“Please Stop Calling My Aunt Carl, I Love Her.”
(This corresponds to: Potassium, Sodium, Calcium, Magnesium, Aluminum, Carbon, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold)

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17
Q

How are metals that are less reactive than carbon extracted?

A

Zn, Fe, Pb, H can be extracted using carbon reduction.

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18
Q

How are reactive metals (more reactive than carbon) extracted?

A

K, Na, Ca, Mg, Al are extracted using electrolysis. The ore is melted, and then electricity is used to separate the metal from its compounds or using a more reactive metal (displacement)

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19
Q

What is the primary ore used for extracting iron?

A

The primary ore used is hematite, which contains iron(III) oxide.

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20
Q

What primary reaction occurs in the extraction of Fe?

A

The primary reaction is the reduction of iron(III) oxide (Fe₂O₃) using carbon (coke) in a blast furnace.
The reaction can be summarized as follows: Fe2O3 (s) + 3CO (g) → 2Fe (I) + 3CO2 (g)

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21
Q

What is the role of carbon (coke) in the extraction of iron?

A

Carbon acts as a reducing agent, reacting with hematite in a blast furnace to produce iron and carbon dioxide.

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22
Q

What is the overall reaction for the extraction of iron from iron(III) oxide?

A

The overall reaction is: Iron(III) oxide + Carbon → Carbon dioxide + Iron.

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23
Q

Why is carbon monoxide a more effective reducing agent in the extraction process?

A

Carbon monoxide is more effective because it is a gas, allowing it to mix easily with solid hematite.

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24
Q

What impurities are commonly found in hematite, and how are they removed during iron extraction?

A

Impurities such as silicon dioxide are removed by adding calcium carbonate (limestone), which forms calcium silicate (slag) when it reacts with calcium oxide.

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25
What environmental concern is associated with the extraction of iron?
The iron extraction process generates significant amounts of carbon dioxide, contributing to climate change.
26
What is done with the slag produced during the iron extraction process?
The slag can be repurposed for road surfacing due to its lower density and practical applications.
27
In the extraction of iron, what is the reducing agent?
Carbon: it is taking away the oxygen
28
In the extraction of iron, what is the oxidizing agent?
The hematite: it is providing the oxygen
29
In the extraction of iron, what is being oxidized?
The carbon
30
In the extraction of iron, what is being reduced?
The hematite
31
What is the first step in the extraction of iron from hematite?
Carbon (coke) and oxygen for carbon dioxide
32
Why is the reaction between carbon and oxygen essential in the extraction of iron?
This reaction is essential because it produces carbon dioxide and generates the heat needed for the subsequent reactions. (exothermic) The heat facilitates the reduction of iron(III) oxide by carbon monoxide, which is produced in the next steps.
33
What is the 2nd step in the extraction of iron?
The reduction of carbon dioxide to carbon monoxide: CO2 (g) + C (s) → 2CO (g) It is carbon monoxide that is the reducing agent.
34
What is the last step in the extraction of iron?
The reduction of iron(III) oxide by carbon monoxide: Fe2O3 (s) + 3CO (g) → 2Fe (I) + 3CO2 (g)
35
What is the primary impurity found in iron ore during extraction?
The primary impurity is silicon dioxide (SiO₂), commonly found in the form of sand or rock within the iron ore.
36
Why do the impurities in hematite need to be removed in the extraction of iron?
Because, it would make the iron weaker
37
How is silicon dioxide removed during the extraction of iron?
Silicon dioxide is removed by adding limestone (calcium carbonate) to the blast furnace. It reacts with the impurity to form calcium silicate (slag).
38
What reaction occurs when limestone is added to the blast furnace to remove impurities?
The thermal decomposition of calcium carbonate (limestone) to produce calcium oxide: CaCO3 (s) → CaO (s) + CO2 (g) The formation of slag: CaO (s) + SiO2 (s) → CaSiO3 (l)
39
What is coke?
Carbon
40
What is slag?
Calcium silicate (CaO)
41
What is the symbol for silicone dioxide?
SiO2
42
What happens to the slag produced from the removal of impurities?
The slag is less dense than molten iron, so it floats on top and can be easily removed. It can be repurposed for making road surfaces and other applications.
43
What is a half equation?
A half equation is a representation of the oxidation or reduction process occurring at one of the electrodes during electrolysis. (Show what is happening in terms of gaining or losing electrons)
44
What occurs at the cathode during electrolysis?
At the cathode, reduction occurs, where cations gain electrons.
45
What occurs at the anode during electrolysis?
At the anode, oxidation occurs, where anions lose electrons.
46
What are the steps to formulate a half-equation?
1) Write a balanced chemical equation. 2) Identify elements or ionic compounds. 3) Compare charges on both sides to determine electron gain or loss. 4) Write the half equation based on the identified changes.
47
Why is it necessary to balance half equations during electrolysis?
Balancing is necessary to ensure that the number of electrons lost in oxidation equals the number gained in reduction.
48
What is the role of spectator ions in a chemical reaction?
Spectator ions are ions that do not change during the reaction, remaining unchanged throughout the process.
49
If an ion is positive, what has happened in terms of electrons?
It has lost electrons
50
If an ion is negative, what has happened in terms of electrons?
It has gained electrons
51
What is the importance of balancing half equations?
Balancing ensures that the number of electrons lost in oxidation equals the number gained in reduction.
52
What is electrolysis?
Electrolysis is a decomposition reaction that requires the input of electrical energy to break down ionic substances.
53
Why can only ionic substances undergo electrolysis?
Ionic substances conduct electricity when molten or dissolved in water, allowing for the movement of ions. It also needs to have both cations and anions present that can both react.
54
What happens to ionic substances during electrolysis?
Ions are attracted to electrodes: cations move to the cathode and anions to the anode, where they undergo reduction and oxidation, respectively.
55
What type of reaction is electrolysis?
It is an example of a redox reaction
56
What is the positive electrode called?
The anode. This is because anions (negative ions) are attracted to the positive.
57
What is the negative electrode called?
The cathode. Because positive ions (cations) are attracted to negative.
58
What is the anode electrode made from?
The positive side is attached to graphite/ platinum (some sort of cathode that conducts electricity but does not react).
59
What is the chemical that we are doing the electrolysis of called?
The chemical that we are putting it into (the electrodes) is the chemical we are doing the electrolysis of. That chemical is called the electrolyte.
60
What occurs at the cathode in electrolysis?
* The cathode (-) attracts cations (+) * The cathode is (-) because it has lots of electrons => supplied by the battery/power supply * The cation will gain electrons until it becomes neutral * The element made will be a (l) due to the high temp. the process is happening at **REDUCTION**
61
What occurs at the anode in electrolysis?
* The anode (+) attracts anions (-) * The anode is (+) because electrons are flowing away from it and back to the battery (absence if electrons) * When anion comes into contact with anode, it will lose electrons until it becomes neutral * The element made will be a (l) due to the high temp. the process is happening at **OXIDATION**
62
How is Al extracted?
Using electrolysis because it is more reactive than C. The Al compound is melted (requires lots of energy).
63
What happens to the solution after electrolysis is complete?
A solution of the unreacted ions is left behind, which may affect the pH of the solution.
64
What is the general rule for reactivity of ions in electrolysis?
More reactive ions will preferentially discharge over less reactive ions during electrolysis.
65
What is the name of the ore from which aluminum is extracted?
The ore is called bauxite, which mainly contains aluminum oxide.
66
Why does aluminum oxide have a high melting point?
Aluminum oxide has a high melting point due to strong electrostatic forces between the aluminum ions (Al³⁺) and oxide ions (O²⁻).
67
What type of electrodes are used in the electrolysis of aluminum oxide?
Graphite electrodes are used in the electrolysis of aluminum oxide.
68
What products are formed at the cathode during the electrolysis of aluminum oxide?
Molten aluminum metal is produced at the cathode. => can then be frozen and molded
69
What happens at the anode during the electrolysis of aluminum oxide?
Oxygen gas is produced at the anode, which reacts with the graphite electrode to form carbon dioxide. The anodes erode over time due to the reaction with oxygen and therefore needs to be replaced over time.
70
What are the downsides of the extraction of Al using electrolysis?
* High energy demand => usually from non-renewable recourses (bad for environment) * Expensive (because of high energy)
71
Why do anodes need to be replaced during aluminum electrolysis?
The anodes erode over time due to the reaction with oxygen, producing carbon dioxide.
72
Describe the reduction process occurring at the cathode during the extraction of Al.
Aluminum ions (Al³⁺) gain three electrons to become aluminum metal (Al), which is a reduction process.
73
Describe the oxidation process occurring at the anode during the extraction of Al.
Oxide ions (O²⁻) lose two electrons to form oxygen gas (O₂) during the oxidation process.
74
Why is aluminum extraction economically significant despite its high energy costs?
Aluminum is lightweight and strong, making it valuable for industries such as aerospace.
75
What factor contributes to the huge size of industrial electrolysis cells for aluminum extraction?
To produce large quantities of aluminum economically, industrial cells are significantly larger, often compared to the size of a swimming pool.
76
What is the basic reaction taking place during the electrolysis of aluminum oxide?
The breakdown of aluminum oxide (Al2O3) into aluminum and oxygen gas.
77
Draw a diagram of the extraction of Al
78
What is the symbol equation fro what occures at the anode and cathode during the extraction fo Al?
79
How can high energy demands be lowered in th extraction fo Al?
By adding cryolite (Na3AlF6)
80
What is cryolite?
Cryolite is a mineral composed of sodium aluminum fluoride (Na3AlF6) used as an electrolyte in the extraction of aluminum.
81
Why is cryolite added to aluminum oxide during electrolysis?
Cryolite lowers the melting point of aluminum oxide, making the process more energy-efficient.
82
How does the addition of cryolite reduce energy demands?
* Cryolite helps lower the melting point of aluminum oxide from around 2072°C to about 1000-1200°C, making the process more energy-efficient. (less energy needed to keep moletn) * By increasing the conductivity of the molten aluminum oxide, cryolite facilitates a more efficient transfer of electricity.
83
What are the chemical components of cryolite?
Cryolite is primarily composed of sodium aluminum fluoride (Na3AlF6).
84
What additional benefit does cryolite provide in the context of aluminum extraction?
It reduces environmental impact by lowering energy requirements, which can minimize reliance on non-renewable energy sources.
85
In what physical state is cryolite used during the aluminum extraction process?
Cryolite is used in its molten state as part of the electrolyte mixture.
86
Why does cryolite help to lower the mpt of Al2O3?
Because the cryolite contains ions with much lower charg. Mixing these ions in the electrolyte lowers the mpt due to weaker electrostatic forces.
87
Why does cryolite increase the conductivity of Al2O3 in the extraction fo Al?
* It decreases the resistance of electricity * Waste less electrical energy
88
Is cryolite a catalyst?
NOOOO!!! * It is not interfering with the reaction * Does not affect the activation energy * Does not speed up rate of reaction
89
What is required for electrolysis to occur?
An ionic substance that conducts electricity, either in molten form or dissolved in water (aqueous).
90
Why can't solid ionic substances undergo electrolysis?
Solid ionic substances do not conduct electricity; they only conduct when molten or dissolved.
91
What ions do water break down into during electrolysis of solutions?
Water can break down into hydrogen ions (H⁺) and hydroxide ions (OH⁻).
92
How does the position of ions affect their likelihood to undergo oxidation or reduction during electrolysis?
More reactive ions will preferentially lose electrons (oxidation) or gain electrons (reduction) at the electrodes.
93
What happens to the remaining ions in the solution after electrolysis of solutions?
The remaining ions that do not participate in reactions will be left in the solution, affecting its properties.
94
What happens during electrolysis of an aqueous solution?
The solution contains ions that can move freely, allowing for redox reactions at the electrodes.
95
What are the products of electrolysis when NaCl is dissolved in water?
The products are chlorine gas (Cl₂) at the anode and hydrogen gas (H₂) at the cathode.
96
What is produced at the cathode during the electrolysis of sodium hydroxide solution?
Hydrogen gas (H₂) is produced at the cathode.
97
What is produced at the anode during the electrolysis of sodium chloride solution?
Chlorine gas (Cl₂) is produced at the anode.
98
How doe we know the reactivity of ions?
The most reactive element will be the least reactive ion. So, the least reactive element will be the one to form at the electrode. For example, between H+ ions and Na+ ions, H+ ions are the most reactive, so hydrogen will form at the cathode. This is because hydrogen is the least reactive (loses electrons the least easily) and therefore H+ is the more reactive (gains electrons more easily).
99
What is the reactivity of halogens (and the other ions that lose electrons)?
100

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