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C2 > 7-Electrolysis > Flashcards

7-Electrolysis Flashcards

0
Q

What is electrolysis?

A

The breaking down of an ionic compound, making elements, using electricity.

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1
Q

When are ions free to move?

A

When ionic substances are melted/dissolved in water.

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2
Q

What happens at the cathode (negative electrode)?

A

Positively charged ions gain electrons by reduction.

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3
Q

What happens at the anode (positive electrode)?

A

Negatively charged ions lose electrons by oxidation.

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4
Q

What is OILRIG?

A 
Oxidation
Is
Less
Reduction
Is
Gain
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5
Q

What is a chemical reaction with both reduction and oxidation?

A

A redox reaction.

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6
Q

If the electrolyte (melted/dissolved substance) contains mix of ions how do you know what products are formed?

A

By the reactivity of the elements used.

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7
Q

What is aluminium ore called?

A

Bauxite.

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8
Q

What is aluminium or purified into?

A

Aluminium oxide from which aluminium is extracted.

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9
Q

Why must aluminium be molten?

A

So ions are free to move.

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10
Q

Why is aluminium oxide first dissolved in cryolite?

A

To lower the melting point, making it cheaper and safer.

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11
Q

What happens during electrolysis of aluminium ore?

A

Electrodes made of carbon.
Aluminium ions attracted to negative electrode.
Aluminium formed at negative electrode.
Aluminium dense so sinks to bottom and is collected.
Oxide ions attracted to positive electrode.
Oxygen formed and reacts with carbon to form CO2.
Carbon electrode disappears slowly an has to be replaced.

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12
Q

What is the reaction at the negative electrode when extracting aluminium from aluminium ore?

A

Al3+ + 3e- —> Al

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13
Q

What is the reaction at the positive electrode when extracting aluminium from aluminium ore?

A

2O2- —> O2 + 4e-

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14
Q

What is the overall reaction for extracting aluminium from aluminium ore?

A

2Al2O3 —> 4Al + 3O2

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15
Q

What is produced at the positive electrode in the electrolysis of brine?

A

Chlorine gas.

16
Q

What is produced at the negative electrode in electrolysis of brine?

A

Hydrogen gas.

17
Q

What is collected at the bottom of the cell in electrolysis of brine?

A

Sodium hydroxide solution.

18
Q

What is brine?

A

Sodium chloride solution.

19
Q

What are the uses for chlorine?

A

To kill bacteria in drinking water and swimming pools.

To manufacture hydrochloric acid, disinfectants, bleach, and PVC.

20
Q

What are the uses of hydrogen?

A

Used in manufacture of ammonia and margarine.

21
Q

What are the uses of sodium hydroxide?

A

The manufacture of soap paper and ceramics.

22
Q

What is the equation for the electrolysis of brine?

A

Sodium Chloride + Water —> Chlorine + Hydrogen + Sodium Hydroxide

2NaCl + 2H2O —> Cl2 + H2 + 2NaOH

23
Q

What is the equation for what happens at the positive electrode during electrolysis of brine?

A

2Cl- —> Cl2 + 2e-

24
Q

What is the equation for what happens at the negative electrode during electrolysis of brine?

A

2H+ + 2e- —> H2

25
Q

What are two other uses of electrolysis?

A

Electroplating.

Purification (of copper).

26
Q

Why would you electroplate an object?

A

To protect it (from corrosion.

To make it look nice.

27
Q

What do you need to purify copper using electrolysis?

A

Positive electrode made of impure copper.
Negative electrode made of pure copper.
Solution must contain copper ions.

28
Q

How do you purify copper during electrolysis?

A

At positive electrode copper ions pass into solution.
At negative electro copper ions move towards it to gain electrons and form copper atoms which stick to pure copper electrode.
Negative electrode gets bigger whilst positive dissolves into nothing.
Impurities fall to bottom.

29
Q

What reaction happens at the positive electrode during purification of copper?

A

Cu —> Cu2+ + 2e-

30
Q

What reaction happens at the negative electrode during purification of copper?

A

Cu2+ + 2e- —> Cu

31
Q

What will be produced at the negative electrode if the metal in the solution reacts with acids to produce hydrogen?

A

Hydrogen.

32
Q

If the solution is a chloride, bromide or iodide what is produced at the positive electrode?

A

Chlorine, Bromine or Iodine.

33
Q

What are the pros of electrolysing brine?

A

3 very important materials are produced from one raw material.
Brine is a renewable source that’s readily available.
Brine is cheap.
Products formed are used in many different industries to make a variety of things.
Minimal waste produced.

34
Q

What are the cons of electrolysing brine?

A

Process of electrolysis very expensive as requires lots of electrical energy.
Production of electricity in power stations adds to pollution.
Hydrogen and chlorine can be produced by other methods much more cheaply.

C2 (6 decks)

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