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science :((( > Electrolysis > Flashcards

Electrolysis Flashcards

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1
Q

Oxidation

A

Loses electrons, gains oxygen

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2
Q

Reduction

A

Gains electrons, loses oxygen

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3
Q

When metals react

A

They lose electrons group 1 loses 1, group 2 loses 2 etc

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4
Q

Reactivity of metals depends on

A

How easily they lose electrons

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5
Q

Metals react with oxygen

A

Form metal oxide

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6
Q

Calcium and oxygen reaction

A

2Ca + O*2 = 2CaO

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7
Q

If a metal reacts with water

A

Hydrogen is always produced

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8
Q

Sodium and water reaction

A

Sodium + water –> sodium hydroxide + hydrogen

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9
Q

Potassium with water

A

2K+2H2O –> 2KO + H2

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10
Q

Metals react with acid, what gas produced?

A

Hydrogen

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11
Q

Magnesium and sulfuric acid equation

A

H2SO4 + Mg –> MgSO4 + H2

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12
Q

Magnesium and hydrochloric acid

A

Magnesium + hydrochloric acid –> magnesium chloride + hydrogen

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13
Q

Ore

A

a substance from which it is economically viable to extract a metal

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14
Q

Iron ore

A

Haematite

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15
Q

Aluminium ore

A

Bauxite - red mineral made of aluminium oxide + iron oxides

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16
Q

The more reactive a metal

A

The more extreme the method of extraction

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17
Q

Unreactive metals e.g. Gold Platinum

A

Found as their uncombined element, no extraction needed

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18
Q

Silver

A

Can be decomposed by smelting alone

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19
Q

Metals less reactive than carbon

A

Can be extracted by heating the metal oxide with carbon

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20
Q

Metals less reactive than carbon equation

A

iron oxide + carbon -> iron + carbon dioxide (displacement and reduction reaction)

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21
Q

Metals more reactive than carbon

A

Must be extracted by electrolysis as carbon can’t displace them from their compounds

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22
Q

Metals less reactive than hydrogen

A

Don’t react with acids as they cannot displace them

23
Q

Electrolysis simple def

A

The breaking up of an ionic compound using electricity - uses lost of energy so expensive

24
Q

Displacement reactions

A

A more reactive element displaces a less reactive element from a compound

25
Q

Why are displacement reactions redox reactions - oxygen

A

More reactive metal gains oxygen therefore is oxidised/less reactive loses oxygen so is reduced

26
Q

Why are displacement reactions redox reactions - electrons

A

More reactive metal loses electrons therefore is oxidised/less reactive gains electrons so is reduced

27
Q

Oxidation half equation (Mg

A

Mg -> Mg2+ + 2e

28
Q

Reduction half equation (Zn

A

Zn2+ + 2e -> Zn

29
Q

Overall equation

A

Zn2+ + Mg -> Zn + Mg2+

30
Q

Why can metals not displace other metals

A

Those metals would also need to be extracted and this would require a more reactive metal

31
Q

For electrolysis to happen, solid ionic compounds must be

A

Molten or aqueous (dissolved in water)

32
Q

Cathode

A

Negative electrode

33
Q

Cation

A

Positive ion, attracted to cathode

34
Q

Anode

A

Positive electrode

35
Q

Anion

A

Negative ion, attracted to anode

36
Q

Electrolyte

A

Substance that has been decomposed/broken up by passing electricity through it

37
Q

Why is copper being extracted from low grade ores

A

High grade ores are running out
New extraction methods have been developed which use less energy, making it economically viable

38
Q

Phytomining process

A

Plants are grown in soil containing low grade ores
Copper compounds are absorbed through the roots
Copper becomes part of the plant, concentrating it in a smaller volume
Plants are harvested and burned as fuel
The ash contains a high % of copper
Copper is extracted from the ash by traditional methods

39
Q

Bioleaching

A

Bacteria which feeds on low grade copper ores absorb copper compounds - they are grown in them to produce a solution of copper compounds known as a leachate

40
Q

Copper can be extracted from leachate or ash by

A

Electrolysis
Displacement with scrap iron

41
Q

Pros of scrap iron

A

It is plentiful and cheap, and can displace copper as it is more reactive

42
Q

Pros of phytomining/bioleaching

A

Uses less energy, able to extract from low grade ores, avoids mining (no need to dig/transport/dispose of rock; plants are used as fuel before copper is extracted and it is classed as CO2 neutral

43
Q

Cons of phytomining/bioleaching

A

Slower batch process, may not produce copper when needed, takes up land that could be used for growing food, energy is still needed for electrolysis

44
Q

During electrolysis at the cathode

A

Positive ions (cations) move towards the cathode. The positive ions gain electrons (however many they originally lost)

45
Q

Cathode electrolysis example copper

A

Cu2+ + 2e -> Cu (reduction)

46
Q

During electrolysis at the anode

A

Negative ions (anions) move towards the anode. The negative ions lose however many electrons they originally gained

47
Q

Anode electrolysis example chlorine

A

Cl- -> Cl + e or 2Cl- -> Cl2 + 2e (as an element, chlorine exists as diatomic molecules) (this is oxidation)

48
Q

Electrolysis of molten ionic compounds (simpler as there is only one type of pos/neg ion

A

Metallic element from ionic compound is formed at the cathode; non metallic element formed at anode

49
Q

Why is aluminium dissolved in molten Cryolite before electrolysis

A

To lower the melting point

50
Q

Aluminium cathode

A

Whole base of tank - large surface area, Al forms at bottom and is easy to siphon off

51
Q

Anodes eroding with _ oxide

A

Oxygen reacts with the hot carbon anode to form carbon dioxide

52
Q

Electrolysis of aqueous ionic compounds

A

There are also pos and neg ions from the water present - H+ and OH-. H+ and the metal are attracted to the cathode - one will gain e-s and become an element; the other will stay as an ion in an ionic compound. Same with anode

53
Q

At the cathode aqueous ionic compounds electrolysis
(metal is MORE reactive than hydrogen)

A

If the metal is more reactive than hydrogen, it will lose electrons more easily than hydrogen. The hydrogen ion will gain e-s more easily and become reduced (2H+ + 2e -> H2) The metal ion reamins in the solution and we form H2 gas at the cathode

54
Q

At the cathode aqueous ionic compounds electrolysis
(metal is LESS reactive than hydrogen)

A

If there ARE halide ions (Cl-, BR-, I-)
They will each lose 1 electron and are oxidised, they are diatomic so the equation is 2Cl- -> Cl2 + 2e- and the OH- ion stay in the solution

If there are NO halide ions
The OH- ion loses an electron. 4 OH- ions give up 4 electrons to form water and oxygen at the anode (4OH- -> 2H2O + O2 +4e)
The other type of anion stays in the solution.

science :((( (13 decks)

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