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Chemistry > 4 - Electrochemistry > Flashcards

4 - Electrochemistry Flashcards

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1
Q

What is the use of Ionic Half Equations?

A

To show clearly what is oxidised or reduced

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2
Q

What do Ionic Half Equations show?

A

If a particle is oxidised or reduced

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3
Q

Give an example of an Ionic Half Equation showing oxidation

A

M –> Mx+ + xe-

M = metal

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4
Q

Why do Metals show differences in reactivity?

A
  • They have different atomic radii. The larger the atom, the weaker the electrostatic forces attracting the electrons to the nucleus, making it easier to lose them and react
  • The less electrons a metal has in it’s outer shell, the less it needs to lose to reach a noble gas electronic configuration, so less energy is required to atract the electrons away and cause the metal to react
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5
Q

What happens when a metal atom reacts with an acid?

A

It loses electrons to gain a noble gas electronic configuration, oxdising and forming a cation

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6
Q

Def. Electrolyte

A

A liquid or aqueous ionic compound that conducts electricity by the movement of ions

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7
Q

What does an electrolyte consist of?

A

A liquid with dissasociated ions

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8
Q

What makes a strong electrolyte?

A

When the ions are completely disassociated and there is a high concentration of ions

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9
Q

Def. Electrolysis

A

The breakdown of an ionic compound when molten or in aqueous solution by the passage of electricity

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10
Q

What occurs at a Cathode generally in electrolysis?

A
  • Metal is formed (or hydrogen)
  • Positive metal ions, cations, are attracted to the cathode and gain electrons to form atoms
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11
Q

What occurs at a Anode generally in electrolysis?

A
  • A non-metal is formed
  • Negative metal ions, anions, are attracted to the cathode and lose electrons to form atoms
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12
Q

Def. Inert Electrode

A

An electrode that does not react or change during electrolysis e.g. carbon or platinum

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13
Q

What type of reaction occurs at the Anode?

A

Oxidation

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14
Q

What type of reaction occurs at the Cathode?

A

Reduction

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15
Q

What happens to electrons during electrolysis?

A

The Anode takes electrons from the Anions and they travel to the Cathode, where they are given to the Cation. As a result, both ions form atoms.

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16
Q

What are the 4 rules about electrolysis in solutions?

A
  1. Unreactive metalslike copper always form at the cathode
  2. If the compound is a polyatomic (e.g. sulfate or a nitrate), the oxygen gas forms at the anode
  3. If a compound contains a reactive etal ion, hydrogen gas forms at the cathode instead of the metal
  4. If the compound contains a halide ion, the halogen gas is produced at the anode
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17
Q

What occurs when water is reduced at the cathode?

A

Hygrogen gas and hydroxide ions are formed.

The hydrogen gas bubbles off while the hydroxide ions remain in the electrolyte, making it alkaline.

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18
Q

What occurs when water is oxidised at the anode?

A

Oxygen gas and hydrogen ions are formed.

The oxygen bubbles off while the hydrogen ions remain in the electrolyte, making it acidic.

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19
Q

What is the simplified formula for the reduction of water?

A

2H+ + 2e- → H2

20
Q

What is the simplified formula for the oxidation of water?

A

2O2- → O2 + 4e-

21
Q

What is the produced at the anode during the electrolysis of concentrated aqueous NaCl?

A

Chlorine gas

22
Q

What is the produced at the anode during the electrolysis of dilute aqueous NaCl?

A

Oxygen gas

23
Q

Where is water on the reactivity series of metals?

A

Between Aluminium and Zinc

24
Q

Where is water on the reactivity series of non-metals?

A

Between Chlorine and Bromine

25
Q

What is the main ore containing aluminium?

A

Bauxite

26
Q

What is the role of Bauxite?

A

To extract Aluminium through electrolysis

27
Q

Why is Aluminium Oxide not simply dissolved in water for electrolysis?

A

Aluminium is too reactive to be obtained - you get hydrogen gas instead.

This is why molten Aluminuim Oxide is used.

28
Q

What temperature does Aluminium Oxide melt at?

A

1200°C

29
Q

Why is Cryolite used in the electrolysis of Aluminium Oxide?

A

This is because as Aluminium Oxide dissolved in it, it’s melting point goes down from 1200°C to 900°C, so less energy is used. This means that the Aluminium Oxide can also conduct electricity.

30
Q

Describe the arrangements of the eletrodes in the industrial electrolysis of Aluminium

A

The bottom of a container is lined whith the carbon cathode, so the aluminium collects against it, at the bottom, and multiple carbon anodes are lowered into the fluid, by which oxygen gas is produced.

31
Q

What happens to the carbon anodes in the industrial electrolysis of Aluminium?

A

They react and combust with the oxgen gastht is formed

32
Q

How are metals electroplated?

A

Electrodes that are not inert are used so they electrolyse. This causethe anode to lose mass and this mass is gained in the cathode in the form of plating

33
Q

What happens when copper (II) sulfate is electrolysed with copper elecrodes?

A

Instead of oxygen formingat the anode, the anode dissolves into the electrolyte and copper metal is plated onto the cathode

34
Q

Why are some materials electroplated?

A
  • To improve their appearance
  • To increase their resistance to corrosion
35
Q

Which metals can be reduced by carbon?

A

Metals zinc and below on the reactivity series

36
Q

Why is carbon used to displace metals instead of other metals such as aluminium?

A

Aluminium and more reactive metals are expensive as they can only be obtained by electrolysis - the process is cheaper when carbn is used as crbon is much more abundant and cheap.

37
Q

How are reactive metals extracted from their ores?

A

By electrolysis

38
Q

What are the necessary inputs for the blast furnace?

A
  • Hot air
  • Hematite (F2O3), which often contains some sandstone (SiO2)
  • Charcoal (impure C)
  • Limestone (CaCo3)
39
Q

What five reactions take place in a blast furnace in word form?

A
  1. Coke combusts to form carbon dioxide to heat the blast furnace
  2. More coke reacts with carbon dioxide to form carbon monoxide
  3. Carbon monxide, the reducing agent, reduces haematite to form molten iron metal
  4. The limestine thermally decomposes into lime and carbon dioxide
  5. Lime reacts with sand to form slag, a waste material used for building roads
40
Q

What does a Hydrogen-oxygen fuel cell do?

A

A hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product

41
Q

What are the advantages of a hydrogen fuel cell?

A
  • They do not produce any pollution: the only product is water whereas petrol engines produce carbon dioxide, and oxides of nitrogen
  • They release more energy per kilogram than either petrol or diesel
  • No power is lost in transmission as there are no moving parts, unlike an internal combustion engine
  • Quieter so less noise pollution compared to a petrol engine
42
Q

What are the disadvantages of a hydrogen-oxygen fuel cell

A
  • Materials used in producing fuel cells are expensive
  • Hydrogen is more difficult and expensive to store compared to petrol as it is very flammable and easily explodes when under pressure
  • Fuel cells are affected by low temperatures, becoming less efficient
  • There are only a small number of hydrogen filling stations across the country
  • Hydrogen is often obtained by methods that involve the combustion of fossil fuels, therefore releasing carbon dioxide and other pollutants into the atmosphere
43
Q

What occurs in the anode of the hydrogen-poxygen fuel cell?

A

Hydrogen gas is ionised and becomes H+, giving it’s electrons to the anode

H2 → 2H+ + 2e-

44
Q

What occurs at the cathode of the hydrogen-oxygen fuel cell?

A

H+ ions, oxygen gas and electrons react to form water

4H+ + 4e- + O2 → 2H2O

45
Q

What five reactions take place in a blast furnace in formula form?

A

C(s) + O2(g)→ CO2(g)

C(s) + CO2(g)→ 2CO(g)

3CO(g) + Fe2O3(g)→ 2Fe(l) + 3CO2(g)

CaCO3(g) → CaO(s) + CO2(g)

CaO(g) + SiO2(s)→ CaSiO3(l)

Chemistry (12 decks)

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