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Chemistry > Electrolysis > Flashcards

Electrolysis Flashcards

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1
Q

What is electrolysis?

A

Electrolysis means ‘splitting up with electricity’, this uses an electric current to break down ionic compounds.

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2
Q

What is the compound broken down by electrolysis called?

A

The compound broken down by electrolysis is called the electrolyte.

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3
Q

In electrolysis, where will the positive ions in the electrolyte move?

A

The positive ions in the electrolyte will move towards the cathode (the negative electrode) and gain electrons (where they are reduced).

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4
Q

In electrolysis, where will the negative ions in the electrolyte move?

A

The negative ions in the electrolyte will move towards the anode (the positive electrode) and lose electrons (they are oxidised).

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5
Q

What does OILRIG stand for?

A

Oxidation
Is
Loss
Reduction
Is
Gain

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6
Q

What does PANiC stand for?

A

Positive
Anode
Negative
(is)
Cathode

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7
Q

When ions move to the oppositely charged electrode what does this create?

A

When ions move to the oppositely charged electrode this creates a flow of charge through the electrolyte.

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8
Q

What happens when ions gain or lose electrons?

A

When ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.

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9
Q

Why can’t an ionic solid be electrolysed?

A

An ionic solid can’t be electrolysed because the ions are in fixed positions and can’t move.

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10
Q

What type of ionic compound can be electrolysed and why?

A

Molten ionic compounds can be electrolysed because the ions can move freely and conduct electricity.

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11
Q

How do you show how lead bromide is broken up into their elements using half equations?

A

Example of lead bromide being broke into their elements:

Lead being reduced:
Pb^(2+) + 2e^(-) —> Pb

Bromine being oxidised
2Br^(-) —> Br2 + 2e^(-)

  • Look at CGP book to understand how they properly look on pg. 58
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12
Q

What the difference in ions moving to the cathode and anode other than their charges?

A
  • Metal (positive) ions are reduced to the element at cathode
  • Non-metal (negative) ions are oxidised to the element at the anode
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13
Q

If a metal is too reactive to be reduced with carbon what happens?

A

If a metal is too reactive to be reduced with carbon or reacts with carbon then electrolysis can be used to extract it.

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14
Q

What is a disadvantage of electrolysis and why?

A

Extracting methods via electrolysis is very expensive as lots of energy is required to melt the ore and produce the required current.

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15
Q

What compound does bauxite contain which has aluminium?

A

Bauxite contains aluminium oxide, Al2O3

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16
Q

How is aluminium extracted from the ore, bauxite, by electrolysis?

A
  • Aluminium is mixed with cryolite
  • The molten mixture contains free ions so it’ll conduct electricity
  • The positive Al^(3+) ions are attracted to the cathode where they pick up 3 electrons and turn into neutral aluminium atoms
  • These atoms then sink to the bottom of electrolysis tank
  • The negative o^(2-) ions are attracted to the anode where they lose 2 electrons and the neutral oxygen atoms will combine to form O2 molecules
17
Q

When extracting aluminium from bauxite by electrolysis, why is cryolite used?

A

Cryolite is used because aluminium oxide has a very high melting temperature so cryolite is used to lower the melting point.

18
Q

What is the half equation for aluminium oxide being reduced/oxidised during electrolysis?

A

Aluminium being reduced:
Al^(3+) + 3e^(-) —> Al

Oxygen being oxidised:
2O^(2-) —> O2 + 4e^(-)

19
Q

What is the overall equation for aluminium oxide being broken down?

A
  • Aluminium oxide —> aluminium + oxygen
  • 2Al2O3(l) —> 4Al(l) + 3O2(g)
20
Q

What is the anode made of in aluminium oxide electrolysis and what does this mean?

A
  • The anode is made of carbon
  • Oxygen reacts with it to produce carbon dioxide
  • This means the anode needs to be replaced regularly
21
Q

When doing electrolysis on aqueous solutions, what else other than the ions will be present?

A

There will be hydrogen ions and hydroxide ions from the water.

22
Q

At the cathode, what will happen if the metal ions are more reactive than the hydrogen ions (H^+)?
At the cathode, what will happen if the metal ions are less reactive than the hydrogen ions (H^+)

A

*At the cathode, if the metal ions are more reactive than the hydrogen ions, hydrogen gas will be produced
* At the cathode, if the metal ions are less reactive than the hydrogen ions, a solid layer of pure metal will be produced

23
Q

At the anode, what will happen if hydroxide (OH^-) and halide ions are present?
At the anode, what will happen if hydroxide (OH^-) and no halide ions are present?

A
  • At the anode, if hydroxide (OH^-) and halide ions are present, the halogens will be formed
  • At the anode, if hydroxide (OH^-) and no halide ions are present, then the hydroxide ions are discharged and oxygen will be formed
24
Q

When drawing apparatus for an electrolysis experiment, you need to include what power supply?

A

When drawing apparatus for an electrolysis experiment, you need to include a d.c. (direct current) power supply.

25
Q

In electrolysis with aqueous solutions, how do you know if oxygen is produced?

A

At the anode, bubbles will be produced if oxygen is produced.

26
Q

How test if chlorine was produced at the anode?

A

Chlorine bleaches damp litmus paper, turning it white.

27
Q

How test if oxygen was produced at the anode?

A

Oxygen will relight a glowing splint.

28
Q

How test if hydrogen was produced at the cathode?

A

Hydrogen makes a ‘squeaky pop’ with a lighted splint.

29
Q

What is the half equation if hydrogen is produced at the cathode?

A

2H^(+) + 2e^(-) —> H2

*Look at pg.59 in CGP book to see it clearer

30
Q

What is the half equation is chlorine is produced at the anode?

A

2Cl^(-) —> Cl2 + 2e^(-)
or
2Cl^(-) - 2el^(-) —> Cl2

31
Q

What is the half equation is hydroxide is produced at the anode?

A

4OH^(-) —> O2 + 2H2O + 4e^(-)
or
4OH^(-) - 4e^(-) —> O2 + 2H2O

Chemistry (6 decks)

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