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IGCSE Chemistry > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

Define electrolysis.

A

breakdown of an ionic compound, when molten or in aqueous solution, by the passage of an electric current

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2
Q

What is the anode?

A

the positive electrode

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3
Q

What is the cathode?

A

the negative electron

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4
Q

What is the electrolyte?

A

the molten or aqueous substance that undergoes electrolysis

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5
Q

What process occurs at the anode?

A

oxidation

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6
Q

What process occurs at the cathode?

A

reduction

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7
Q

Why are metal objects electroplated?

A

to improve their appearance and resistance to corrosion

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8
Q

What process makes metal objects more resistant to corrosion and with improved appearance?

A

electroplating

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9
Q

What does a hydrogen–oxygen fuel cell do?

A

uses hydrogen and oxygen to produce electricity with water as the only chemical product

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10
Q

Electrolysis of MOLTEN LEAD(II) BROMIDE: product at the anode

A

bromine

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11
Q

Electrolysis of MOLTEN LEAD(II) BROMIDE: product at the cathode

A

lead

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12
Q

Electrolysis of MOLTEN LEAD(II) BROMIDE: observations

A

cathode: silvery solid
anode: brown gas

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13
Q

Electrolysis of concentrated aqueous NaCl: product at the anode

A

chlorine

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14
Q

Electrolysis of concentrated aqueous NaCl: product at the cathode

A

hydrogen

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15
Q

Electrolysis of concentrated aqueous NaCl: observations

A

cathode: colourless gas, lit splint squeaky pop

anode: pale yellow-green gas (turns UI red and bleaches red litmus)

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16
Q

Electrolysis of dilute sulfuric acid: product at the anode

A

oxygen

17
Q

Electrolysis of dilute sulfuric acid: product at the cathode

A

hydrogen

18
Q

Electrolysis of dilute sulfuric acid: observations

A

anode: colourless gas, relights glowing splint
cathode: colourless gas, lit splint squeaky pop

19
Q

What forms at the cathode in the electrolysis of aqueous electrolytes?

A

cation below hydrogen in reactivity series- metal forms

cation above hydrogen- hydrogen gas forms, metal ion stays in solution

20
Q

What forms at the anode in the electrolysis of aqueous electrolytes?

A
  • halide ions (like Cl– , Br– or I–) present - the element will form (chlorine etc)
  • other anions (eg sulfate, nitrate) - oxygen will form
  • from the dissociation of OH– ions as nitrate/sulfate ions are more reactive than OH- ions
21
Q

What forms at the anode in the electrolysis of molten electrolytes?

A

non-metal

22
Q

What forms at the cathode in the electrolysis of molten electrolytes?

A

metal

23
Q

What forms in the anode?

A

non-metals (other than hydrogen)

24
Q

What forms in the cathode?

A

metals, or hydrogen

25
Q

Advantages of hydrogen fuel cell

A

high energy density, high fuel efficiency, minimal pollution

26
Q

Disadvantages of hydrogen fuel cells

A

hydrogen has to be produced (often involving burning fossil fuels), stored as a compressed gas so difficult to transport, highly flammable

27
Q

a hydrogen–oxygen fuel cell uses

A

hydrogen and oxygen to produce electricity with water as the only chemical product

28
Q

Describe how metals are electroplated.

A

metal ions migrate via a solution from a positive electrode to a negative one

29
Q

why are metal objects electroplated

A

improve their appearance and resistance to corrosion.

30
Q

Describe the extraction of aluminium from purified bauxite / aluminium oxide

A
  • Bauxite is first purified to produce aluminium oxide, Al2O3
  • Aluminium oxide is then dissolved in molten cryolite
    • This is because aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive
    • The resulting mixture has a lower melting point without interfering with the reaction
  • The mixture is placed in an electrolysis cell, made from steel, lined with graphite
  • The graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrodes
31
Q

aluminium cathode

A

Al3+ + 3e- → Al

32
Q

aluminium anode

A

2O2- → O2 + 4e-

33
Q

aluminium overall

A

2Al2O3 → 4Al + 3O2

34
Q

Explain why the carbon anode has to be replaced regularly.

A

carbon reacts with oxygen and forms carbon dioxide

35
Q

aqueous copper (II) sulphate products in graphite

A

cathode: copper
anode: oxygen

36
Q

aqueous copper (II) sulphate products in copper

A

cathode: copper
anode: copper

37
Q

reduction of hydrogen

A

2H+(aq) + 2e– → H2(g)

38
Q

hydroxide equation

A

4OH–(aq)→2H2O(l)+O2(g)+4e–

IGCSE Chemistry (18 decks)

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