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Chemistry OCR GCSE > C3.4 Electrolysis > Flashcards

C3.4 Electrolysis Flashcards

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1
Q

Electrolysis

A

Process where electric current is passed through a compound causing a chemical change
Also splits ionic compounds
Electrolyte - compound in its liquid state or in solution that can conduct electricity and contains mobile ions
2 electrodes made form metal or graphite to conduct electricity to the electrolyte:
Negative cathode
Positive anode
Electrical supply such as a power pack or battery

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2
Q

Negative electrode

A

Cathode

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3
Q

Positive electrode

A

Anode

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4
Q

What happens to positive ions during electrolysis

A

Gain electrons at cathode and become atoms

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5
Q

What happens to negative ions during electrolysis

A

Lose electrons at anode and become atoms

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6
Q

What might happen if atoms formed in electrolysis are non metal atoms

A

Covalent bonds will form between them, making molecules

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7
Q

Positive ions electrolysis name

A

Cations

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8
Q

Negative ions electrolysis name

A

Anions

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9
Q

Binary ionic compound

A

Contains only 2 elements

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10
Q

Discharged

A

When ions become atoms or molecules at an electrode

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11
Q

Inert electrodes

A

Don’t change during electrolysis
Made from unreactive metals such as copper and platinum, or graphite
Used for many ionic compounds in their liquid state or aqueous solution

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12
Q

What happens during the electrolysis of water

A

H2O(l) ⇌ H+(aq) + OH-(aq)
Hydrogen ions discharged at cathode, in gas state
Hydroxide ions discharged at the anode, forming water and oxygen in its gas state

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13
Q

Electroplating

A

Type of electolysis that uses non inert electrodes
They change during the electrolysis

Anode loses mass
Cathode gains mass

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14
Q

What is cathode in electroplating

A

The object to coat

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15
Q

What is anode in electroplating

A

Piece of the metal to coat with

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16
Q

What is electrolyte in electroplating

A

Solution containing ions of the coating metal

17
Q

How metals are purified with electrolysis

A

Both electrodes made from the same metal
Anode: impure metal
Cathode: very pure metal

Cathode gains metal atoms and increases in mass
Anode loses metal atoms and reduces in mass
Impurities collect under the anode

18
Q

Molten electrolysis

A

Compound is split up
Positive ion attracted to negative electrode
Negative ion attracted to positive electrode
Ions are discharged at the electrodes - become atoms
Bunsen burner needed
Might not be used as high amount of energy needed in order to get the compound in the molten state.

19
Q

Aqueous electrolysis

A

At the Cathode (-)
Least reactive ion discharged (often hydrogen) Link to reactivity series

At the Anode (+)
If halide present, it will be discharged and a halogen is formed
If no halide, then oxygen given off

ONLY 1 ION CAN BE DISCHARGED AT AN ELECTRODE

20
Q

Reactivity series

A

Potassium. Sodium. Calcium. Magnesium. Aluminium. (Carbon). Zinc. Iron. Tin. Lead. (Hydrogen). Copper. Silver. Gold
Platinum

Most reactive. Least reactive

Please
Stop
Calling
Me
A
Careless
Zebra
Instead
Try
Learning
HoW
Copper
Saves
Gold
Platinum

21
Q

Which electrode does reduction and oxidisation take place?

A

Reduction - cathode (red-cat)
Oxidisation - anode

22
Q

Example electrolysis half equations

A

Lead bromide:
Anode reaction: 2Br- —> Br2 + 2e- : bromine (non metal) is produced
Cathode reaction: Pb²+ + 2e- —> Pb : lead (metal) is produced
(Molten electrolysis)

Sodium chloride:
Anode Reaction: 2Cl- —> Cl2 + 2e-
Cathode Reaction: 2H+ + 2e- —> H2
(Aqueous electrolysis)

Remember format of half equations for anode and cathode.
NB: THESE QUESTIONS CAN BE VERY UNPREDICTABLE AND ARE ONLY 1 OR 2 MARKS IN A TEST. THERE IS NO CLEAR WAY AND WE WERE NOT CLEARLY TAUGHT.

23
Q

Electrode half equation for Copper Chloride (CuCl2)

A

Anode: 2Cl- —> Cl2 + 2e-
Cathode: Cu 2+ + 2e- —> Cu

24
Q

Electrode half equation for Dilute Sodium Chloride

A

Anode: 2Cl- -> Cl2 + 2e-
Cathode: 2H+ + 2e- -> H2

25
Q

Electrode half equation for Concentrated Sodium Chloride (NaCl)

A

Anode: 2Cl- —> Cl2 + 2e-
Cathode: 2H+ + 2e- —> H2

26
Q

Electrode half equation for Concentrated Copper (II) Sulfate (CuSO4)

A

Anode: 4OH- -> O2 + 2H2O + 4e-
Cathode: Cu2+ + 2e- —> Cu

27
Q

Electrode half equation for Sodium Sulfate (Na2SO4)

A

Anode: 4OH- —> O2 + 2H2O + 4e-
Cathode: 2H+ + 2e- —> H2

28
Q

Why ionic compounds in the solid state cannot be electrolysed

A

Do not have ions that are free to move around as they are fixed within the lattice structure
Ionic compounds only conduct electricity when molten or aqueous where ions are free to move around in solution.
Therefore it cannot conduct electricity.

29
Q

half-equation for the discharge of hydroxide ions

A

4OH- -> 2H2O + O2 + 4e-

Chemistry OCR GCSE (16 decks)

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