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Additional Chemistry > C2.7 - Electrolysis > Flashcards

C2.7 - Electrolysis Flashcards

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1
Q

What is electrolysis?

A

Electrolysis means “splitting up with electricity”.

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2
Q

Why does electrolysis occur when ionic substances are molten or dissolved?

A

The ionic substance must be molten or dissolved in solution so the ions are free to move and conduct electricity.

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3
Q

What do the ions break down into during electrolysis?

A

If an electrical current is passed through an ionic compound that is molten or in solution, it breaks down into the elements it is made of and electrolysis occurs.

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4
Q

What is meant by the “electrolyte”?

A

The electrolyte is the substance that is broken down under electrolysis.

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5
Q

What is the positive electrode otherwise known as?

A

The positive electrode is the anode.

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6
Q

What is the negative electrode otherwise known as?

A

The negative electrode is the cathode.

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7
Q

Where do the different ions move in electrolysis?

A

In electrolysis, positive ions move to the negative electrode and negative ions move to the positive electrode.

As ions gain or lose electrons, they become atoms or molecules and are released.

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8
Q

Describe reduction.

A

When positively charged ions reach the negative electrode, they gain electrons to become neutral atoms. This is reduction.

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9
Q

What happens when ions gain 2 electrons?

A

Ions with a single positive charge gain one electron and those with a 2+ charge gain 2 electrons.

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10
Q

Describe oxidation.

A

When negatively charged ions reach the positive electrode, they lose electrons to become atoms. This is oxidation.

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11
Q

What is OILRIG?

A

Oxidation is loss, reduction is gain.

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12
Q

Describe what happens at the negative electrode in the electrolysis of lead bromide.

A

Positive ions are attracted to the negative electrode. The Pb2+ gains 2 electrons to produce lead. (Reduction).

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13
Q

Describe what happens at the positive electrode in the electrolysis of lead bromide.

A

Negative ions are attracted to the positive electrode. The Br- lose one electron each to become one bromine molecule (Br2)

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14
Q

What ions does water contain?

A

Water contains hydrogen ions and hydroxide ions.

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15
Q

In the electrolysis of sodium chloride, why is hydrogen sometimes produced?

A

When aqueous solutions are electrolysed, hydrogen gas is produced at the negative electrode unless the solution contains ions of a metal that is less reactive than hydrogen.

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16
Q

When is oxygen produced in the electroylsis of sodium chloride?

A

When aqueous solutions are electrolysed, oxygen gas is produced at the positive electrode unless the solution contains a high concentration of halide ions (Cl-, Br-, I-).

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17
Q

Why do less reactive metals get produced in electrolysis?

A

The more reactive an element, the keener it is to stay as ions.

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18
Q

What is brine?

A

When sodium chloride is dissolved in water, it is known as brine.

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19
Q

What is produced when sodium chloride is electrolysed?

A

When electrolysed, sodium chloride produces hydogen, chlorine, and sodium hydroxide.

20
Q

What is produced at the negative electrode in the electrolysis of sodium hydroxide?

A

At the negative electrode, two hydrogen ions gain two electrons to become one hydrogen molecule.

21
Q

What is produced at the positive electrode in the electrolysis of sodium hydroxide?

A

At the positive electrode, two chloride ions lose their electrons and become one chlorine molecule.

22
Q

What is left in solution in the electrolysis of sodium chloride?

A

The sodium ions remains in solution as they are more reactive than hydrogen. Hydroxide ions from water are also left behind, hence sodium hydroxide (NaOH) remains in solution.

23
Q

What do half equations show?

A

Half-equuations show reactions at the electrodes.

The number of electrons must remain the same on both sides.

24
Q

What is the half equation at the negative electrode in the electrolysis of sodium chloride?

A

2H+ + 2e - -> H2

25
Q

What is the half equation at the positive electrode in the electrolysis of sodium chloride?

A

2CL- -> Cl2 + 2e-

2CL- - 2e -> CL2

26
Q

What is sodium hydroxide used for?

A

Sodium hydroxide is a very strong alkali and is used to make soap, paper, bleach, to neutralise acids and to control pH.

27
Q

What is chlorine used for?

A

Chlorine is used in the production of bleach and plastics and as a disinfectant.

28
Q

What is hydrogen used for?

A

Hydrogen is used to make margarine and hydrochloric acid.

It is also used for rocket fuel.

29
Q

How is aluminium extracted?

A

Aluminium is more reactive than carbon and so it must be extracted from its ore using electrolysis.

30
Q

How is aluminium found?

A

Aluminium is an abundant ore, but it is found naturally in compounds.

31
Q

How is bauxite prepared for electrolysis?

A

Bauxite is mined and purified to leave a white powder, ALO3, which undergoes electrolysis.

32
Q

What is the problem with carrying out electrolysis on aluminium oxide?

A

Aluminium oxide has a high melting point of over 2000 degrees, so this would require a lot of energy and would be expensive, so the oxide is dissolved in molten cryolite.

33
Q

What is cryolite?

A

Cryolite is a less common ore of aluminium.

34
Q

What does cryolite do to make electrolysis easier?

A

Cryolite brings the temperature down to about 900 degrees, which makes the process cheaper.

35
Q

What are the electrodes made of in aluminium electrolysis?

A

The electrodes are made of carbon (graphite), which is a good conductor of electricity.

36
Q

What forms at what electrode in the electrolysis of aluminium oxide?

A

Aluminium forms at the negative electrode and oxygen forms at the positive electrode.

37
Q

What is the half equation for the negative electrode of aluminium electrolysis?

A

AI3+ + 3e - -> Al

38
Q

What is the half equation for the positive electrode of aluminium electrolysis?

A

202 -> 02 + 4e-

39
Q

Why is carbon dioxide produced?

A

The oxygen reacts with carbon to produce carbon dioxide, which means that the positive electrode is “eaten away” and needs eventual replacement.

40
Q

What is electroplating?

A

Electroplating uses electrolysis to put a thin coating of metal onto an object.

41
Q

What is usually used in electroplating?

A

Gold, silver, and chromium plating are often used.

42
Q

Why is electroplating done?

A

This may be done to:

Reduce costs by using a thin layer of metal instead of the pure metal.

Make an object look more attractive

Protect a metal object from corroding.

Increase the hardness of a surface.

43
Q

What acts as the electrodes in electroplating?

A

The object to be plated is the negative electrode.

The positive electrode is made from the plating metal.

44
Q

What is the electrolyte in electroplating?

A

The electrolyte contains ions of the plating metal.

45
Q

What happens at the positive electrode in electroplating?

A

At the positive electrode, atoms of the plating metal lose electrons to form metal ions that go into solution.

46
Q

What happens at the negative electrode in electroplating?

A

At the negative electrode, metal ions from the solution gain electrons to form metal atoms, which are deposited on the object to be plated.

47
Q

Give some examples of electroplating.

A

Copper may be used as a means for electronic circuits to conduct electricity.

Silver is expensive so coating brass with it is cheaper and attractive.

Additional Chemistry (6 decks)

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