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Chem 3: Elements of the Sea > ES3: Electrolysis > Flashcards

ES3: Electrolysis Flashcards

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1
Q

Define “electrolysis”

A

The breaking down of a compound into its elements by passing an electric current through an ionic substance molten or in solution

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2
Q

What is an electrolyte?

A

Liquid that conducts electricity in electrolysis

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3
Q

What does an electrolyte contain?

A

A molten/dissolved ionic substance

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4
Q

Why does the ionic substance need to be molten/dissolved?

A

So the ions are free to move and carry charge

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5
Q

Which electrode is negative?

A

Cathode

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6
Q

Which electrode is positive?

A

Anode

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7
Q

What happens at the cathode?(4)

A
  • Cathode is negative
  • Attracts cations because of the opposite charge
  • Cations migrate to it
  • There they gain electrons and become an atiom
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8
Q

What happens at the anode?(4)

A
  • Anode is positive
  • Attracts anions because of the opposite charge
  • Anions migrate to it
  • There they lose electrons and become an atiom
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9
Q

Describe a method for setting up electrolysis.(6)

A
  • Use wires + clips to connect each electrode to the power supply
  • Electrode at the positive pole is the anode
  • Electrode at the negative pole is the cathode
  • Use inert electrodes (e.g carbon/platinum) so they don’t react + interfere with electrolysis
  • Place electrodes in the beaker containing the electrolyte, making sure they don’t touch each other
  • Turn the power supply on
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10
Q

What do products forming as metals look like?

A

A thin layer on the surface of the cathode

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11
Q

What do products forming as gases look like?

A

Bubbles at the cathode/anode

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12
Q

What happens to metal ions in the electrolysis of molten compounds?

A

They are positive and so move to the cathode and are reduced there

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13
Q

Give a half equation for the reduction of zinc.

A

Zn2+(l) + 2e- ====> Zn(s)

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14
Q

What happens to non-metal ions in electrolysis of molten compounds?

A

They are negative and so move to the anode and are oxidised there

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15
Q

Why are the products of the electrolysis of ionic solutions hard to determine?

A

The H+ and OH- ions from the water are competing with the ions

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16
Q

What is produced in the electrolysis of ionic solutions at the cathode when the metal is more reactive than hydrogen?

A

Hydrogen gas

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17
Q

What metals are more reactive than hydrogen?(3)

A
  • Group 1 metals
  • Group 2 metals
  • Aluminium
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18
Q

Give the equation for the production of hydrogen at the cathode from water?

A

2H20 (l) + 2e- ===> 2OH- (aq) + H2 (g)

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19
Q

What is the pH surrounding the cathode in the electrolysis of ionic solutions when the metal is more reactive than hydrogen?

A

Alkaline because of the OH- ions surrounding the cathode

20
Q

What is produced in the electrolysis of ionic solutions at the cathode when the metal is less reactive than hydrogen?

A

The metal is formed

21
Q

What is produced at the cathode if there is an acid in the solution?

A

Hydrogen gas

22
Q

Give the equation for the production of hydrogen at the cathode from hydrogen ions?

A

2H+(aq) + 2e- ===> H2 (g)

23
Q

What is produced in the electrolysis of ionic solutions at the anode when the non metal is a sulfate/nitrate?

A

Oxygen gas

24
Q

Give the equation for the production of oxygen at the anode from water.

A

H2O (l) ====> O2 (g) + 4e- + 4H+ (aq)

25
Q

What is the pH surrounding the anode in the electrolysis of ionic solutions when the non metal is a sulfate/nitrate like?

A

Acid because of the H+ ions surrounding the cathode

26
Q

What is formed at the anode in the electrolysis of a concentrated ionic solution with a halide ?

A

The halogen gas

27
Q

What is the pH of the solution left behind after the production of hydrogen at the cathode and why?

A

Alkaline because of the hydroxide ions left behind in the solution

28
Q

What is formed at the anode in the electrolysis of a dilute ionic solution with a halide ?

A

Oxygen is formed

29
Q

What is formed at the anode in the electrolysis of a solution with a hydroxide ?

A

Oxygen is formed

30
Q

Give the half equation for the formation of oxygen at the anode.

A

4OH- (aq) ===> O2 (g) + 2H2O (l) + 2e-

31
Q

What is the pH of the solution left behind after the production of oxygen at the anode and why?

A

Neutral because the OH- ions have been reduced

32
Q

Describe what happens when the solution contains the same metal as the one both the electrodes are made of. Use copper as the example. (5)

A
  • At the anode, oxidation occurs and electrons are lost:
    (Cu (s) ====> Cu2+ (aq) + 2e-)
  • Copper ions enter the solution and become attached to the cathode
  • At the cathode, reduction occurs and electrons are gained:
    (Cu2+ (aq) + 2e- ===> Cu (s))
  • Copper atoms plate the pure copper cathode
  • The concentration of the solution remains constant
33
Q

What substance is the anode made of when the solution contains the same metal as the one both the electrodes are made of (e.g copper) ?

A

The impure metal (e.g impure copper)

34
Q

What substance is the anode made of when the solution contains the same metal as the one both the electrodes are made of (e.g copper) ?

A

Pure metal (e.g pure copper)

35
Q

What is used as an electrolyte in copper electroplating?

A

CuSO4

36
Q

What two uses are there for using the same metal for the electrodes and the solution in electrolysis?

A
  • Electroplating objects with the metal coating

- Purifying impure metals

37
Q

What happens to the pure cathode when using the same metal for the electrodes and the solution in electrolysis?

A

Increases its mass

38
Q

What happens to the impure anode when using the same metal for the electrodes and the solution in electrolysis?

A

It shrinks

39
Q

How can chlorine be produced as a gas?

A

From the electrolysis of brine

40
Q

What is brine?

A

A solution of water with a high concentration of halide salts

41
Q

What halide salts in brine is mainly made up of?

A

Sodium chloride, with some bromine and iodine salts

42
Q

Name 3 places brine can be found

A
  • Occurring naturally as seawater
  • Occurring naturally in salt lake
  • By dissolving rock salt in water
43
Q

How can bromine be produced using displacement?(3)

A
  • Bubble chlorine gas through brine
  • Collect the bromine produced
  • Condense it into a liquid and purify it
44
Q

Give the ionic equation for the displacement of bromine with chlorine

A

2Br-(aq) + Cl2 (g) ===> 2Cl- (aq) + Br2 (aq)

45
Q

How can iodine be produced using displacement?(3)

A
  • Bubble chlorine gas through brine
  • Collect the iodine produced
  • Purify it and condense it into a grey solid
46
Q

Give a half equation for the reduction of bromine.

A

2Br-(l) ====> Br2 (g) + 2e-

Chem 3: Elements of the Sea (7 decks)

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