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Y12 Chem > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

Electrolysis

A

Electrolysis is the decomposition of a liquid electrolyte using a direct current of electricity

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2
Q

PANIC

A 
Positive 
Anode
Negative 
Is
Cathode
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3
Q

Electrolyte

A

Ionic compound that is molten or dissolved in water

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4
Q

Cathode

A

Negative electrode

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5
Q

Anode

A

Positive electrode

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6
Q

Cation

A

Positive ion

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7
Q

Anion

A

Negative ion

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8
Q

Inert electrode

A

Metal strips or graphite rods placed into the liquid and connected to a supply of electricity

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9
Q

Give one use of electrolysis in industry

A

Extracting aluminium from its ore

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10
Q

How does electrolysis work?

A
  • All electrolytes conduct electricity because they have free ions that can move and carry charge
  • ions are attracted to the oppositely charged electrode
  • Positive cations at the negative electrode (cathode) gain electrons to become atoms
  • When electrons are gained this is reduction
  • the negative anions At the positive electrode (anode) lose electrons to become atoms, which may combine to form diatomic molecules for elements e.g chlorine
  • When electrons are lost this is oxidation
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11
Q

What are electrodes made from ?

A

Carbon

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12
Q

Why graphite is used for electrodes

A
  • it is a good conductors of electricity

- It is unreactive

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13
Q

Describe what is observed at the cathode with molten lead (ii) bromide

A
  • Positive ion Pb2+ attracted to negative cathode
  • Half equation: Pb2+ + 2e- —> Pb
    Observations: silvery grey liquid formed, which sinks to the bottom
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14
Q

Describe what is observed at the anode with molten lead (ii) bromide

A

Negative ion Br- attracted to positive anode
Half equation - 2Br- —> Br2 + 2e-
Observations - red-brown pungent has evolved

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15
Q

Describe what is observed at the cathode with molten lithium chloride

A

Positive ion Li+ attracted to negative cathode
Half equation - Li+ + e- —> Li
Observations - molten silvery grey liquid formed

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16
Q

Describe what is observed at the anode with molten lithium chloride

A

Negative ion Cl- attracted to anode
Half equation - 2Cl- —> Cl2 + 2e-
Observations - pale green pungent gas evolved. Oxidation reaction

17
Q

Describe the products of electrolysis of dilute sulfuric acid and half equations for the reactions at the anode and cathode

A

Cathode: Positive ion H+ attracted to cathode
2H+ + 2e- —> H2
Observations - Colourless odourless gas evolved

Anode: Negative ions OH- and SO4 2- attracted to anode
4OH- —> O2 + 2H2O + 4e-
Colourless, odourless gas evolved

18
Q

State what is observed at the anode during electrolysis of dilute sulfuric acid

A

The negative ions OH- and SO4 2- are attracted to the anode. The PH- ion is preferentially discharged instead of the SO4 2- ion
It takes four electrons to be removed at the anode to produce one O2 molecule

19
Q

Why is the volume of hydrogen gas twice the volume of oxygen gas when using electrolysis of dilute sulfuric acid (2)

A
  • because two electrons given up at the cathode produce one H2 molecule, whereas it takes four electrons to be removed at the anode to produce one O2 molecule
  • Four electrons lost and gained will produce two H2 molecules for every one O2 molecule
20
Q

Name aluminium ore

A

Bauxite

21
Q

Reaction at the anode and cathode of extracting aluminium

A

Cathode
Al3+ + 3e- —> Al
Anode
2O2- —> O2 + 4e-
Reaction at cathode is reduction because aluminium ions are gaining electrons
Reaction at anode is oxidation because oxide ions are losing electrons

22
Q

Why does carbon have to be replaced periodically ?

A

It wears away as it reacts with oxygen

C + O2 —> CO2

23
Q

Describe the industrial extraction of aluminium (3)

A
  • Bauxite is purified by mixing it with sodium hydroxide solution
  • The alumina (aluminium oxide) in the ore dissolves in molten cryolite to reduce the operating temperature and increase its conductivity
  • Crust of aluminium oxide keeps the heat in. Operating temperature is between 900 and 1000 degrees
24
Q

Disadvantage of electrolysis of aluminium

A
  • Extraction of aluminium is expensive because the cost of electricity is high and a high temperature is needed to keep the aluminium oxide molten
25
Q

Advantages of recycling aluminium (3)

A
  • Aluminium oxide crust keeps some heat in, saving money
  • the expense of recycling aluminium is only a fraction of the cost of producing new aluminium from bauxite
  • This is why it’s important to recycle materials such as aluminium, it saves resources, saves energy, prevents waste going to landfill and costs less
26
Q

Why is cryolite used ?

A

The use of cryolite increases the conductivity and reduces the operating temperature, saving money

27
Q

Draw the working out f the products of the electrolysis of dilute sulfuric acid solution

A

-

29
Q

Definition of electrolyte

A

The electrolyte is the liquid or solution that conducts electrify and is decomposed by it

30
Q

Inert electrodes definition

A

Electrodes that do not take part in the reactions

31
Q

What are common electrolytes

A

Molten ionic compounds and aqueous ionic compounds

32
Q

What happens if a molten metal oxide is electrolysed

A

Oxygen gas is produced at the anode

Observations include a colourless, odourless gas being evolved

33
Q

Observations of sodium and iodine at the cathode/anode

A

Silvery grey liquid formed

Purple, pungent gas

Y12 Chem (16 decks)

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