C4 Electrolysis (pg 135)

Question 1

What is Elecrolysis?

Answer 1

It means ‘Splitting up with Electricity’

Electrolysis use an electrical current to cause a reaction.

Question 2

What happens during Electrolysis?

Answer 2

An electric current is passed through an electrolyte (a molten or dissolved ionic compound).

The ions move towards the electrodes, where they react and the compound decomposes.

Question 3

When positive ions in the electrolyte move, what do they move towards?

Answer 3

They move towards the cathode (-ve electrode) and gain electrons (they are reduced)

Question 4

Where will the ‘negative ions’ in the electrolyte move towards?

Answer 4

they will move towards the anode (+ve electrode) and lose electrons (they are oxidised)

This creates a flow of charge through the electrolyte as ions travel to the electrodes.

Question 5

What happens when ions gain or lose electrons?

Answer 5

they form the uncharged element and are discharged from the electrolyte.

Question 6

What is an electrolye?

Answer 6

Its just a liquid or a solution that can conduct electricity.

Question 7

What is a electrode?

Answer 7

it is a solid that conducts electricity and is submerged in the electrolyte.

Question 8

What is a cathode?

Answer 8

the negatively charged electrode by which electrons enter an electrical device.

Question 9

What is an anode?

Answer 9

the positively charged electrode by which the electrons leave an electrical device

Question 10

What do oxidised mean?

Answer 10

undergo or cause to undergo a reaction in which electrons are lost to another species.

(iron (II) compounds are slowly oxidized by air to form iron (III) compounds

Question 11

Electrolysis of Molten Ionic Solids forms what?

Answer 11

Elements

Question 12

Why cant an ionic solid be electrolysed?

Answer 12

because the ions are in fixed positions and cant move.

Question 13

Why can Molten ionic compounds be electrolysed?

Answer 13

because the ions can move freely and conduct electricity.

Question 14

Molten ionic liquids, e.g. lead bromide, are always brokent up into their elements, how?

Answer 14

Positive metals ions are reduced to the element at the cathode:

Pb2+ + 2e- &raquo_space;» Pb

Negative non-metal ions are oxidised to the element at the anode:

2Br- &raquo_space;» Br2 + 2e-

Question 15

Why should electrodes be inert? (not chemically reactive)

Answer 15

so they don’t react with the electroylte.

Question 16

Metals can be extracted from their ores using what?

Answer 16

Electrolysis

Question 17

When can electrolysis be used to extract metal?

Answer 17

If a metal is too reactive to be reduced with carbon (page 133) or reacts with carbon, then electrolysis can be used to extract it.

Extracting metals via this method is very expensive as lots of energh is required to melt the ore and produce the required current.

Question 18

Aluminium is extracted from the ore bauxite by what?

Answer 18

electrolysis

Bauxite contains aluminium oxide, Al2O3

Question 19

What is Bauxite?

Answer 19

Bauxites are rocks that contain minerals mostly from the group of aluminium hydroxide, mainly gibbsite (Al(OH)3), or aluminium oxide hydrate boehmite ALOOH) and rarel amorpous gel (Al(OH)3)

It is a white red, yellow or brown calylike substance comprising aluminium oxides and hydroxides often with such impurities as iron oxides. It is the chief ore of aluminium.
(an impure mixture of earthy hydrous aluminium oxides and hydroxides that is the principal source of aluminum

Question 20

Aluminium oxide has a very high melting temperature, what is mixed to lower the melting point?

Answer 20

It gets mixed with cryolite to lower the melting point.

(cryolite is an aluminium based compound with a lower melting point than aluminium oxide)

Question 21

A molten mixture contains free ions, what do this mean?

Answer 21

it will conduct electricity

Question 22

What do molten mean?

Answer 22

fused or liquefied by heat. melted molten lava.

Question 23

A positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms….. what happens next?

Answer 23

These then sink to the bottom of the electrolysis tank.

Question 24

The negative O2- ions are attracted to the positive electrode where they each lose two electrons. what happens next…..?

Answer 24

the neutral oxygen atoms will then combine to form O2 molecules.

(see diagram on page 135)

Question 25

At the negative electrode, Metals form positive ions, so what are they attracted to?

Answer 25

negative electrode.

Question 26

Non-metals form negative ions so they’re attracted to what?

Answer 26

positive electrode

Question 27

Tell me the symbol equation for?

Aluminium oxide &raquo_space;» aluminium + Oxygen

Answer 27

2Al2O3(l) &raquo_space;»» 4Al(l) + 3O2(g)

Question 28

A Student carried out electrolysis on molten calcium chloride. What is produced at:

a) the anode?
b) the cathode?

Answer 28

a) chlorine gas Cl2
b) Calcium atoms Ca

(it would be useful for your exams to learn the products of electrolysis of molten lead bromide)

Question 29

What is the products of electrolysis of molten lead bromide, PbBr2(l)

Answer 29

Molten lead bromide, PbBr(l) is an electrolyte.

during electrolysis: Pb2+ ions gain electrons at the cathode and become Pb atoms.

Br- ions lose electrons at the anode and become Br atoms, which pair up to form Br2

(during the electrolysis of molten lead bromide, the bromide ions are converted to bromine atoms and the lead ions are converted to lead atoms)