Electrolysis Flashcards

1
Q

Why can’t solid ionic compounds conduct electricity

A

Because the ions are locked in place and aren’t free to move, so they can’t carry charge

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2
Q

Why do we melt solid ionic compounds for electrolysis

A

The forces are broken so the ions are free to move so they can conduct electricity

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3
Q

What is electrolyte

A

A liquid or solution that can conduct electricity

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4
Q

What does molten mean

A

Melted

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5
Q

What are electrodes made out of

A

Usually graphite or a metal
(Needs to conduct electricity)

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6
Q

What is the name of the negative electrode

A

Cathode
- covered with electrons from energy source

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7
Q

What is the positive electrode called

A

Anode
- lacks electrons

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8
Q

What is attracted to the cathode

A

Positive ions

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9
Q

What is attracted to the anode

A

Negative ions

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10
Q

Which electrode is on the left and which is on the right

A

Cathode - left
Anode - right

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11
Q

What happens when positive ions are attracted to the cathode

A

They gain enough electrons to become atoms
- gaining electrons is a reduction reaction

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12
Q

What happens when negative ions are attracted to the anode

A

They lose electrons to become atoms
- losing electrons is an oxidation reaction

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13
Q

Electrolysis of lead bromide takes place
PbBr2
What are the half equations for each electrode

A

Br has a negative 2 charge
Pb had a positive 2 charge

Pb ions will go to the electrode and gain 2 electrons to become Pb
Pb —> Pb^2+ + 2e-

Br ions will go to the anode and will lose 2 electrons to become Br atoms
2Br- - 2e- —> Br2

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14
Q

What is electrolysis

A
  • Passing an electric current through a substance
  • to break down the substance into elements
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15
Q

List the reactivity series
(Please stop laughing calling me a careless zebra instead try learning how copper saves gold)

A

Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminum
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver gold

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16
Q

What are the 2 methods of extracting metals

A

Reduction using carbon:
- metals that are less reactive than carbon can be extracted using reduction of carbon
- the metal oxide reacts with carbon to produce the metal and carbon dioxide
- the metal oxide is reduced and the carbon is oxidised

Electrolysis:
- if the metal is more reactive than carbon, it can be extracted by electrolysis (expensive and requires lots of energy)

17
Q

Describe the electrolysis of aluminum oxide (bauxite)

A
  • electrolysis can be used to extract metals from their ore, when the metal is too reactive to be reduced by carbon
  • aluminum is extracted from the ore bauxite, which contains aluminum oxide (Al2O3)

1) aluminum oxide has a very high melting point so it’s mixed with cryolite which reduced the melting point.
- the reduced the amount of energy used, reducing costs

2) the molten mixture contains ions free to move, so when we pass a current through the substance, it will conduct electricity

3) the positive Al^3+ ions will be attracted to the cathode and gain 3 electrons to become Al atoms (reduction)
Al3+ + 3e- —> Al
4) the negative O^2- ions will get attracted to the anode where they will lose 2 electrons to become Oxygen atoms (oxidation )
O^2- - 2e- —> O or
O^2- —> O + 2e-
The oxygen atoms will bond to form O2 molecules, so we double the equation
2O^2- —> 2O + 4e-

5) the electrode are made of graphite which is a form of carbon, so the O2 molecules released at the anode will reach with graphite to form carbon dioxide
C + O2 —> CO2

18
Q

Describe the electrolysis of an aqueous solution (dissolved in water)

A
  • in an aqueous solution, as well as the ions from the ionic compound, there will also be hydrogen H+ ions and hydroxide OH- ions from the water
  • this is because water molecules ionise to form these ions

At the cathode:
- if the metal produced at the cathode is more reactive than hydrogen, hydrogen gas will be produced
- if the metal is less reactive than hydrogen, a solid layer of the metal will be produced, coating the cathode

At the anode:
- if halide ions are present, the halogen will be formed
- if no halide ions are present, the OH- ions will be discharged as oxygen gas (and water will be formed)

19
Q

Describe the elctrolysis of copper sulfate solution

A
  • copper sulfate is written as CuSO4
    With the ions Cu^2+ and SO4^2-
  • along with water, there are additional H+ and OH- ions too

At the cathode:
- the Cu^2+ and H+ ions will be attracted to the cathode. Cu ions will gain 2 electrons to become copper
- because copper is less reactive than hydrogen, it will be produced and coat the cathode with a thin layer
Cu2+ + 2e- —> Cu (reduction)

At the anode:
- the SO4^2- and OH- ions will be attracted to the anode.
- because there are no halide ions present, OH- will discharge as oxygen gas (and produce water)
OH- - e- —> O2 + H2O
Balanced:
4OH- - 4e- —> O2 + 2H2O

20
Q

Describe the electrolysis of sodium chloride solution

A
  • sodium chloride is written as NaCl with the ions Na+ and Cl-
  • because it’s an aqueous solution there are additional H+ and OH- ions too

At the cathode:
- the Na+ and H+ ions are attracted to the negative cathode
- because sodium is more reactive than hydrogen, the H+ ions will gain an electron and hydrogen atoms
H+ + e- —> H
- hydrogen atoms will then bond to form H2 molecules so we double the equation
2H+ + 2e- —> H2 (reduction)

At the anode :
- the Cl- and and OH- will be attracted to the positive anode
- because Cl- ions are halide ions, they will gain an electron to form chlorine atoms
Cl- - e- —> Cl
- the chlorine atoms will pair to form chlorine molecules so we need to double the equation
2Cl- - 2e- —> 2Cl (oxidation)

21
Q

Uses of electrolysis

A
  • used to electroplate objects
  • this can be for appearance, durability or prevention of corrosion
    (Copper and silver plating)