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Further Additional Chemistry > Topic 3 - Electrolytic Processes > Flashcards

Topic 3 - Electrolytic Processes Flashcards

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1
Q

What is electrolysis?

A

Decomposing a compound using electricity

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2
Q

During electrolysis, what is electricity applied to?

A

An electrolyte (ionic substance either molten or dissolved in water)

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3
Q

In electrolysis, why does the electrolyte have to be molten or dissolved in water?

A

So there are free electrons to conduct electricity, has to be a flow electrons for circuit to be complete

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4
Q

How do the electrons move along the electrolyte in electrolysis?

A

Taken from ions at +ve anode + given to other ions at -ve cathode. As ions gain/lose electrons they become atoms/molecules

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5
Q

How is molten sodium chloride electrolysed?

A
  • Cathode: sodium (Na+) ions reduced (gain electron) becoming sodium atoms
  • Cathode: Na+ + e- –> Na
  • Anode: chlorine (Cl-) ions oxidised (lose electron) + pair up forming chlorine molecules
  • Anode: 2Cl- –> Cl2 + 2e-
  • Sodium collected from cathode for use in street lamps + coolant in some nuclear reactors
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6
Q

What charge does a cation have?

A

Positive

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7
Q

What charge does a cathode have?

A

Negative

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8
Q

What charge does an anode have?

A

Positive

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9
Q

What charge does an anion have?

A

Negative

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10
Q

What always happens in electrolysis?

A

Oxidation + reduction reaction

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11
Q

What is oxidation?

A

Loss of electrons

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12
Q

What is reduction?

A

Gaining electrons

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13
Q

In the electrolysis of molten lead bromide, what forms at the anode and cathode?

A
  • Anode: bromine (g)

- Cathode: lead (l)

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14
Q

What is he half equation for the reaction at the cathode during the electrolysis of molten lead bromide?

A

Pb[2+] + 2e[-] –> Pb

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15
Q

What is he half equation for the reaction at the anode during the electrolysis of molten lead bromide?

A

2Br[-] –> Br2 + 2e[-]

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16
Q

Why do molten ionic compounds electrolyse differently to salts dissolved in water?

A
  • Salts dissolved in water also have H[+] + OH[-] ions
  • At anode, simplest ion discharged
  • At cathode, metal will be discharged if less reactive than hydrogen. If less reactive H discharged
17
Q

How is concentrated sodium chloride solution electrolysed?

A
  • Ions of Na[+], Cl[-], H[+], OH[-]
  • Cathode: 2 H ions take an electron each forming 1 H molecule
  • Anode: 2 Cl ions lose an electron each forming 1 Cl molecule
  • NaOH left in the solution
18
Q

During the electrolysis of copper chloride solution, CuCl2, what are the half equations at the anode and the cathode?

A
  • Cathode: Cu[2+] + 2e[-] –> Cu

- Anode: 2Cl[-] –> Cl2 + 2e[-]

19
Q

During the electrolysis of copper chloride solution, CuCl2, what is produced at the anode and cathode?

A
  • Cathode: copper (s)

- Anode: chlorine (g)

20
Q

During the electrolysis of copper sulfate solution, CuSO4, what are the half equations at the anode and the cathode?

A
  • Cathode: Cu[2+] + 2e[-] –> Cu

- Anode: 4OH[-] –> 2H2O + O2 + 4e[-]

21
Q

During the electrolysis of copper sulfate solution, CuSO4, what is produced at the anode and cathode?

A
  • Cathode: copper (s)

- Anode: oxygen (g)

22
Q

During the electrolysis of sodium sulfate solution, Na2SO4, what are the half equations at the anode and cathode?

A
  • Cathode: 2H[+] + 2e[-] –> H2

- Anode: 4OH[-] –> 2H2O + O2 + 4e[-]

23
Q

During the electrolysis of sodium sulfate solution, Na2SO4, what us produced at the anode and cathode?

A
  • Cathode: hydrogen (g)

- Anode: oxygen (g)

24
Q

During the electrolysis of sodium chloride solution, NaCl, what are the half equations at the anode and cathode?

A
  • Cathode: 2H[+] + 2e[-] –> H2

- Anode: 2Cl[-] –> Cl2 + 2e[-]

25
Q

During the electrolysis of sodium chloride solution, NaCl, what is produced at the anode and cathode?

A
  • Cathode: hydrogen (g)

- Anode: chlorine (g)

26
Q

Why does copper need to be purified by electrolysis?

A
  • Unreactive
  • Can be obtained easily by reduction with carbon from ore
  • Copper produced isn’t pure enough for use in electrical conductors
27
Q

How is electrolysis used to purify copper?

A
  • Electrolyte is copper (II) sulfate w/ Cl[2+] (aq) ions
  • Cathode is pure piece of pure copper
  • Anode is big lump of pure copper that’ll dissolve
  • Electrical supply pulls electrons off copper atoms at anode so they go into solution as Cu[2+] ions
  • Offering electrons at anode to Cu[2+] ions turn them to copper atoms
  • Impurities dropped at anode as sludge, whilst pure copper atoms bond to cathode
  • Pure copper deposited on cathode: Cu[2+] (aq) + 2e[-] –> Cu (s) (copper ions reduced to copper atoms by gaining electrons)
  • Copper dissolved from impure anode: Cu(s) –> Cu[2+] (aq) + 2e[-] (copper ions oxidised to copper ions by losing electrons)
28
Q

Why do the masses of the anode and the cathode change in the electrolysis of copper sulfate solution?

A
  • Uses copper electrodes
  • Copper ions move from anode to cathode
  • Only when impure anode + pure cathode/2 pure copper electrodes
29
Q

How do you demonstrate the change of mass of electrodes in the electrolysis of copper sulfate solution?

A

-Weigh anode + cathode before electrolysis
-Place electrodes in copper sulfate solution + connect to power pack
-After 5 mins, switch off power pack, remove electrodes + dry
-Weigh electrodes again
(Mass of anode decreases as copper ions lost; mass of cathode increases as copper ions deposited)

30
Q

What is electroplating?

A

Coating the surface of a metal with another metal using electricity (through electrolysis)

31
Q

How does electroplating work?

A
  • Cathode: object being electroplated
  • Anode: pure bar of metal used for plating
    e. g.
  • Cathode: brass cup
  • Anode: pure bar of silver
  • Electrolyte: silver nitrate solution
  • Silver ions from electrolyte move towards cathode + metal gets deposited on brass cup
  • Anode keeps silver ions in the solution ‘topped up’
32
Q

What is electroplating used for?

A
  • Decoration: jewellery/decorative items often electroplated w/ metals like gold/silver, improving their appearance
  • Prevention of corrosion: household objects e.g. cutlery + cooking utensils electroplated to prevent corrosion. Metals for protections are unreactive + don’t corrode easily (e.g. nickel, chromium)

Further Additional Chemistry (5 decks)

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