electrolysis

Question 1

define electrolysis

Answer 1

The breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity.

Question 2

define electrodes

Answer 2

The solid electric conductor through which an electric current enters or leaves an electrolytic cell. They are usually made of graphite (carbon) or platinum as these materials are inert (unreactive).

Question 3

anode

Answer 3

The positive electrode of an electrolytic cell. attracts anions

Question 4

cathode

Answer 4

The negative electrode of an electrolytic cell. attracts cations

Question 5

electrolyte

Answer 5

aqueous or molten substance that conducts electricity

Question 6

oxidation and reduction on electrodes

Answer 6

on cathode reduction takes place, as there is a gain of electrons
on anode oxidation takes place, as there is a loss of electrons

Question 7

what is normally attracted towards cathode

Answer 7

metal or hydrogen

Question 8

what is normally attracted towards anode

Answer 8

non metal ions, halides, hydroxide ions

Question 9

general equation at cathode

Answer 9

Mˆn+ + ne- → M

Question 10

general equation at anode

Answer 10

2X- → X2 + 2e-

Question 11

rules for molten electrolytes, (products)

Answer 11

cathode-metal
anode-non-metal

Question 12

rules for aqueous electrolytes, (products)

Answer 12

ions of hydrogen and hydroxide also present
cathode- metal more reactive than hydrogen, hydrogen produced and vice versa
anode-halide ions discharged if present, else oxygen

Question 13

rules for dilute aqueous electrolytes, (products)

Answer 13

due to excess of hydroxide ions, products change
cathode-same rule
anode- oxygen discharged

Question 14

applications for electrolysis

Answer 14

electroplating, copper refinning,electrolysis of concentrated sodium chloride

Question 15

what is electroplating

Answer 15

Coating one metal with a thin layer of another metal either to improve the appearance of an object or to prevent corrosion.

Question 16

explain general setup of electroplating

Answer 16

cathode-object to electroplate
anode-made from metal used to electroplate
electrolyte- solution containing metal ions used to coat object

Question 17

copper refinning

Answer 17

used to obtain 99.9% pure copper, so that it is a good conductor of electricity to be used as wires and cables. Electrodes made of copper

Question 18

process of copper refinning

Answer 18

1. anode= impure copper
   cathode=pure copper
   2.at anode, copper atoms lose electrons and go into solution as copper ions
   = CU -> Cuˆ2+ + 2e-
   3.copper ions attracted towards cathode, gain electrons form copper atoms
   =Cu2+ + 2e- -> Cu
   layer of pure copper built on cathode
2. precious metals that were on impure anode, drop to bottom called anode slime (gold, platinum, sliver)
3. anode loses mass, cathode gains

Question 19

Electrolysis of concentrated sodium chloride solution

Answer 19

industrial process that produces hydrogen chlorine and sodium hydroxide
cathode- hydrogen produced
anode- chlorine produced
sodium ions and hydroxide ions remain in solution, water evaporates and sodium hydroxide left as product

Question 20

uses for hydrogen in electrolysis of concentrated sodium chloride

Answer 20

fuel cell, nylon manufacture, manufacture of margarine

Question 21

uses for chlorine in electrolysis of concentrated sodium chloride

Answer 21

plastics, solvents, water purification

Question 22

uses for sodium hydroxide in electrolysis of concentrated sodium chloride

Answer 22

soap, detergent, paper, dyes

Question 23

why is hydrogen used as a fuel

Answer 23

when hydrogen is combusted, (with oxygen), the only product is water and electricity, meaning it doesnt polute our enviornment, and can be used for car mottors, reaction is exo

Question 24

overall formula for hydrogen fuel cells

Answer 24

2H2(g) + O2(g) → 2H2O(g)

Question 25

what is a fuel cell

Answer 25

electrochemical cell that converts chemical energy from fuel into electricity

Question 26

what happens in process of hydrogen fuel cells

Answer 26

energy is inputted, water electrolysed to produce hydrogen and oxygen both gases captured to be used by fuel cell as energy

Question 27

outline process of electrolysis of aluminium oxide

Answer 27

used to gain pure aluminium, many anodes used, cathode is bottom of container, to gain aluminiu in mass, anode constantly changed, as carbon reacts with oxygen and produce carbon dioxide which is removed as a gas, cryolitte used to lower melting point of aluminium, thus using less electrolysis making process cheaper

Question 28

outline process of electrolysis of dilute sulfuric acid

Answer 28

bubbles seen in both elecrodes, at cathode hydrogen gas formed, at anode hydroxide ions attracted oxygen produced and water,
hydrogen makes squeeky pop
oxygen relights glowing splint

Question 29

observations of electrolisis of molten lead bromide

Answer 29

silvery solid at the cathode

brown gas at the anode

Question 30

observations of electrolisis of concentrated aqueous sodium chloride

Answer 30

colourless gas at cathode, which makes a lighted splint go ‘pop’

pale yellow-green gas at anode, which turns universal indicator red

pale yellow-green gas at anode also bleaches red litmus paper as chlorine is an acidic gas

Question 34

observations of electrolisis of dilute sulfuric acid

Answer 34

colourless gases at both electrodes

cathode gas makes a lighted splint go ‘pop’

anode gas relights a glowing splint

Question 35

observations of electrolisis of aqueous copper sulfate with copper electrodes

Answer 35

anode becomes smaller, cathode becomes bigger

Question 36

advantages and disadvatanges of hydrogen fuel cells

Answer 36

advantage- doesnt produce greenhouse gases, sustainable energy creation
disadvatnage- expensive, non efficient, flammable (hazardous)