electricity

Question 1

what is electrolysis

Answer 1

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

Question 2

electrolysis reaction

Answer 2

• electrolysis is a redox reaction
• anode is a positively charged electrode and is where oxidation occurs
• cathode is a negatively charged electrode and is where reduction occurs

Question 3

electrolysis of molten lead 2 bromide

Answer 3

• electrolyte : molten lead bromide
• anode: red-brown gas bromine released, bromide ions get reduced
• cathode: lead ions get reduced to lead metal which gets deposited on the cathode

Question 4

electrolysis of concentrated hydrochloric acid

Answer 4

electrolyte: concentrated hydrochloric acid
anode: yellow-green gas released as chloride ions get oxidized to chlorine atoms
cathode: colorless gas bubbles released as hydrogen ions are reduced to hydrogen gas

Question 5

electrolysis of concentrated aqueous sodium chloride

Answer 5

• electrolyte: concentrated aqueous sodium chloride
• anode: yellow-green gas released as chloride ions get reduced to chlorine gas
• cathode: since hydrogen ions are more likely to get reduced than sodium ions, the hydrogen ions will get reduced to hydrogen gas and therefore colourless gas bubbles can be seen here
• sodium and hydroxide ions are left in the electrolyte which form sodium hydroxide solution

Question 6

electrolysis of dilute sulfuric acid

Answer 6

• electrolyte: dilute sulfuric acid
• anode: colorless gas bubbles released as hydroxide ions are reduced to oxygen gas
• cathode: colorless gas bubbles seen as hydrogen ions are reduced to hydrogen gas

Question 7

electrolysis of binary molten compound

Answer 7

• for a binary molten compound of a metal and a nonmetal, the cathode product will always be the metal
• the product formed at the anode will always be the nonmetal

Question 8

formation of metals/hydrogen/nonmetals

Answer 8

metals or hydrogen are formed at the negative electrode (cathode) and nonmetals (other than hydrogen) are formed at the positive electrode (anode)

Question 9

electrolysis of aqueous copper 2 sulfate using carbon/platinum electrodes

Answer 9

• electrolyte: aqueous copper 2 sulphate
• anode: colourless gas bubbles released as hydroxide ions are reduced to oxygen has
• cathode: since copper ions are less reactive than hydrogen ions they tend to get reduced and will form copper metal that will get deposited on the cathode

Question 10

electrolysis of aqueous copper 2 sulfate using copper electrodes (also principle for copper refining)

Answer 10

• impure metal is always in the anode (so impure copper)
• cathode is pure copper
• electrolyte is aqueous copper sulphate
• anode: copper atoms at the anode lose electrons, go into solution as ions and are attracted to the chathode where they gain electrons and form now purified copper atoms. The anode thus lose mass and impurities accumulate at the bottom as anodic sludge
• cathode: copper ions get reduced and deposited onto the pure copper causing an increase in its mass and red-brown deposits

Question 11

electrolysis of a specified halide in dilute aqueous solution

Answer 11

• oxygen gas at the cathode
• at anode if metal is below hydrogen in reactivity, the metal will be produced
• if it is above hydrogen, hydrogen gas will be produced

Question 12

concentrated solution

Answer 12

• at anode the halide will be produced

- at cathode it will be the same as for dilute solutions

Question 13

transfer of charge

Answer 13

• during electrolysis the electrons mve from the power sully towards the cathode
• positive ions within the electrolyte move towards the negatively charged electrode which is the cathode
• here they accept electrons from the cathode and either a metal or hydrogen gas is produced
• negative ions within the electrolyte move towards the positvely charged electrode which is the anode

Question 14

what are simple cells

Answer 14

source of electrical energy

Question 15

design of simple cells

Answer 15

two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external circuit

Question 16

effect of reactivity of metal electrodes

Answer 16

• the more reactive metal forms ions more easily, releasing electrons as its atoms forms ions
• the electrons give the more reactive electrode a negative charge and they then flow around the circuit to the copper electrode

Question 17

why do electrodes have to have a difference in reactivity

Answer 17

• the difference in ability of the electrodes to release electrons causes a voltage to be produced
• the greater the difference in the metal’s reactivity then the greater the voltage

Question 18

describe electroplating

Answer 18

• the anode is made from the pure metal used to coat
• the cathode is the object to be electroplated
• the electrolyte is an aqueous solution of a soluble salt of the pure metal at the anode
• after the electrolysis, the anodic metal will be deposited on the cathodic object

Question 19

uses of electroplating

Answer 19

• make metals more resisitant to corrosion or damage

- improve the appearance of metals (e.g shiny)

Question 20

good conductors

Answer 20

• copper (excellent conductor, malleable, easy to work with)
• aluminium steel cored (used in overhead cables, reinforced with steel core, not as goodconductor as copper but less dense and cheaper

Question 21

good insulators

Answer 21

• plastics and ceramics are used as insulators because they do not have electrons to conduct electricity.
• used to cover pylons and wires to prevent electrocution

Question 22

name of extraction of aluminum process

Answer 22

hall-heroult process

Question 23

substances used in hall-heroult process

Answer 23

• aluminium ore is called bauxite which mainly contains aluminium oxide
• metals which lie above carbon in the reactivity series have to be extracted by electrolysis as they are too reactive
• electrolyte is aluminum oxide
• molten cryolite is added to the electrolyte
• graphite electrodes are used

Question 24

why is molten cryolite added to the electrolyte

Answer 24

• to reduce the melting point of the electrolyte

- to improve the conductivity of the electrolyte

Question 25

describe hall-heroult process

Answer 25

- at anode: oxide ions are reduced to form oxygen gas which is released at the anode - at cathode: aluminium ions are reduced to form molten aluminium which can then be extracted from the setup - carbon dioxide may be formed at the anode because the carbo in the electrodes may react with the oxygen to form carbon dioxide. If there is insufficient oxygen, carbon monoxide may also be formed

Question 26

hall-heroult process half-equations

Answer 26

- al3+ + 3e- -> Al - 2O2- - 4e- -> o2 - C (s) + O2(g) -> CO2 (g)