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Chemistry > C3.4 Electrolysis > Flashcards

C3.4 Electrolysis Flashcards

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1
Q

Electrolysis definition

A

An Electric current is used to breakdown an ionic substance

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2
Q

Electrolyte definition

A

The substance being broken down

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3
Q

What substances does electrolysis work on?

A

Only works on substances made up of ions - ionic compounds, these are mostly the compounds of metals and non-metals

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4
Q

When will Electrolysis work?

A

Will only work if the ions in the substance are free to move - will not work on solids but works on liquids, solutions and molten compounds

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5
Q

Cathode

A

Negatively charged electrode, positively charged ions will go here to gain electrons

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6
Q

Anode

A

Positively charged electrode, negatively charged ions will go here to lose electrons

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7
Q

Cation

A

Positive ion - metal

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8
Q

Anion

A

Negative ion - non-metal

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9
Q

What does electrolysis do?

A

Turns ions back into atoms or molecules

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10
Q

What electrode does oxidation occur?

A

Anode

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11
Q

What electrode does Reduction occur?

A

Cathode

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12
Q

What is a REDOX reaction?

A

a reduction-oxidation reaction, a chemical reaction where the oxidation number of an atom, molecule or ion changes by losing or gaining electrons

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13
Q

Test for Oxygen

A

Relights a glowing splint

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14
Q

Test for Hydrogen

A

‘Squeaky pop’ when lit

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15
Q

PANIC

A

Positive Anode Negative Is Cathode

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16
Q

Ionic half equations - sodium chloride

A

Sodium - Na+ + e- –> Na

Chloride - 2Cl- –> Cl2 + e-

17
Q

OILRIG

A

Oxidation Is Loss Reduction Is Gain

18
Q

LIPGIN

A

Loss Is Positive Gain Is Negative

19
Q

REDCAT

A

REDuction CAThode

20
Q

ANOX

A

ANode OXidation

21
Q

What is Brine?

A

An Aqueous solution

22
Q

What do water molecules break up into?

A

Hydrogen ions H+

Hydroxide ions OH-

23
Q

cations - positive ions - discharge series

A

harder –> easier to be discharged

Na+, Mg2+, Al3+, H+, Cu2+

24
Q

anions - negative ions - discharge series

A

harder –> easier to be discharged

SO42-, NO3, OH-,Cl-, Br-, I-

25
Q

if the ion is a halogen will it be discharged over hydroxide ions?

A

yes - halogen is discharged at the anode

26
Q

if the ion is not a halogen will it be discharged over hydroxide ions?

A

no, hydroxide ions from the water are discharged to make water and oxygen gas - other ions stay in solution

27
Q

if + ions (metals) are more reactive than hydrogen what is produced?

A

Hydrogen

- metals more reactive than hydrogen - K, Na, Ca, Mg, Zn, Fe

28
Q

if + ions (metals) are less reactive than hydrogen what is produced?

A

metal

- metals less reactive than hydrogen - Cu, Ag, Au

29
Q

if - ions are not halogens what is produced?

A

oxygen

- negative ions that aren’t halogens - SO42-, NO3-, CO32-

30
Q

what electrodes are normally used in electrolysis?

A

carbon - inert (non-reactive) - don’t take part in the reaction themselves

31
Q

what happens at a copper anode?

A
  • as the anode is not inert, it loses electron and copper ions go into solution - anode gets smaller
    Cu (s) –> Cu2+ (aq) + 2e-
32
Q

what happens at a copper cathode?

A 
copper ions (rather than hydrogen ions) are discharged because they are lower in the discharge series 
Cu2+ (aq) + 2e- --> Cu (s)
33
Q

describe the process of coper refining

A
  • impure copper is used as anode - thin strip of copper used as cathode
  • solution of copper sulphate is used as electrolyte
  • a deposit of impurities from copper anode remain below anode (sludge)
34
Q

what happens in electroplating?

A

metal ions formed at anode are transferred to cathode where they are deposited as metal - plating the object (spoon) as / at the cathode

35
Q

uses for electroplating

A
  • protect other more reactive metals from corrosion - e.g. steel coated in tin to protect it from air and water
  • improve appearance of objects - e.g. jewellery
36
Q

what are the most common plating metals used in electroplating?

A
  • copper
  • chromium
  • nickel
  • silver
  • tin
37
Q

what ore do you get aluminium oxide from?

A

bauxite

38
Q

what is in bauxite?

A

the ore for aluminium oxide - has other metal oxides so have to separate before carrying out electrolysis of aluminium oxide

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