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my chemistry > Electrolysis > Flashcards

Electrolysis Flashcards

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1
Q

What is electrolysis?

A

The breaking down of a compound using electricity

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2
Q

Name of positive electrode

A

Anode ( as it attracts NEGATIVE anions)

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3
Q

Name of negative electrode

A

Cathode ( as it attracts POSITIVE cations)

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4
Q

What are electrodes usually made from

A
  • Graphite (cheap)
  • Platinum (expensive)
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5
Q

requirements for an electrode

A
  • must be a solid that is conductive but inert (unreactive)
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6
Q

what is the electrolyte?

A

the substance to be broken down
-must conduct electricity

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7
Q

Why must the electrolyte be a molten or dissolved ionic compound or a metal?

A
  • needs charged particles that are free to move
  • ionic compounds have charged particles, but they are not free to come in a solid
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8
Q

why do covalent compounds not work for electrolysis

A

Do not have charged particles

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9
Q

Anomaly of covalent compound that can work in electrolysis

A

ammonia

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10
Q

What happens at anode in electrolysis of molten ionic compound?

A

non-metal ions lose electrons to form molecules (oxidised)

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11
Q

Half equation of electrolysis of molten MgCl2 (anode)

A

2Cl- -> Cl2 + 2e-

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12
Q

Half equation of electrolysis of molten MgCl2 (cathode)

A

Mg2+ + 2e- —> Mg

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13
Q

What happens at cathode in electrolysis of molten ionic compound?

A

metal ions gain electrons to form atoms (reduced)

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14
Q

observations at cathode

A
  • solid (metal) formed
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15
Q

observations at anode

A

-effervescence due to gas formed
-(may be liquid in aqueous electrolysis as heat not required)

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16
Q

what happens to ions in water? (aqueous electrolysis)

A

water molecules can break apart (disassociate) and form H+ and OH- ions

17
Q

Complications of aqueous electrolysis

A
  • now 4 types of ion rather than 2 ( 2 positive, 2 negative), so must work out which is attracted to electrode and which remains in solution
18
Q

How to decide which ion reacts at anode ( aqueous electrolysis)

A
  • If halide ion ( Cl-/Br-/I-) is present, element is produced as normal at electrode
  • otherwise O2 and H2O are produced
19
Q

formula for O2 and H2O production at anode (aqueous electrolysis)

A

4OH- –> O2 + 2H20 + 4e-

20
Q

how to decide which ion reacts at cathode ( aqueous electrolysis)

A

-If metal less reactive than Hydrogen, element produced as normal at electrode (gold, silver, copper)
- Otherwise, Hydrogen produced

21
Q

formula for Hydrogen production at Cathode (aqueous electrolysis)

A

2H+ + 2e- —> H2

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