electricity Flashcards
what is electrolysis
the breakdown of an ionic compound, molten or in aqueous solution, by passage of electricity
electrolysis reaction
- 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
electrolysis of molten lead 2 bromide
- 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
electrolysis of concentrated hydrochloric acid
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
electrolysis of concentrated aqueous sodium chloride
- 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
electrolysis of dilute sulfuric acid
- 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
electrolysis of binary molten compound
- 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
formation of metals/hydrogen/nonmetals
metals or hydrogen are formed at the negative electrode (cathode) and nonmetals (other than hydrogen) are formed at the positive electrode (anode)
electrolysis of aqueous copper 2 sulfate using carbon/platinum electrodes
- 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
electrolysis of aqueous copper 2 sulfate using copper electrodes (also principle for copper refining)
- 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
electrolysis of a specified halide in dilute aqueous solution
- 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
concentrated solution
- at anode the halide will be produced
- at cathode it will be the same as for dilute solutions
transfer of charge
- 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
what are simple cells
source of electrical energy
design of simple cells
two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external circuit
effect of reactivity of metal electrodes
- 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
why do electrodes have to have a difference in reactivity
- 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
describe electroplating
- 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
uses of electroplating
- make metals more resisitant to corrosion or damage
- improve the appearance of metals (e.g shiny)
good conductors
- 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
good insulators
- 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
name of extraction of aluminum process
hall-heroult process
substances used in hall-heroult process
- 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
why is molten cryolite added to the electrolyte
- to reduce the melting point of the electrolyte
- to improve the conductivity of the electrolyte
describe hall-heroult process
- 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
hall-heroult process half-equations
- al3+ + 3e- -> Al
- 2O2- - 4e- -> o2
- C (s) + O2(g) -> CO2 (g)
