electrolysis Flashcards
define electrolysis
The breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity.
define electrodes
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).
anode
The positive electrode of an electrolytic cell. attracts anions
cathode
The negative electrode of an electrolytic cell. attracts cations
electrolyte
aqueous or molten substance that conducts electricity
oxidation and reduction on electrodes
on cathode reduction takes place, as there is a gain of electrons
on anode oxidation takes place, as there is a loss of electrons
what is normally attracted towards cathode
metal or hydrogen
what is normally attracted towards anode
non metal ions, halides, hydroxide ions
general equation at cathode
Mˆn+ + ne- → M
general equation at anode
2X- → X2 + 2e-
rules for molten electrolytes, (products)
cathode-metal
anode-non-metal
rules for aqueous electrolytes, (products)
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
rules for dilute aqueous electrolytes, (products)
due to excess of hydroxide ions, products change
cathode-same rule
anode- oxygen discharged
applications for electrolysis
electroplating, copper refinning,electrolysis of concentrated sodium chloride
what is electroplating
Coating one metal with a thin layer of another metal either to improve the appearance of an object or to prevent corrosion.
explain general setup of electroplating
cathode-object to electroplate
anode-made from metal used to electroplate
electrolyte- solution containing metal ions used to coat object
copper refinning
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
process of copper refinning
- 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 - precious metals that were on impure anode, drop to bottom called anode slime (gold, platinum, sliver)
- anode loses mass, cathode gains
Electrolysis of concentrated sodium chloride solution
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
uses for hydrogen in electrolysis of concentrated sodium chloride
fuel cell, nylon manufacture, manufacture of margarine
uses for chlorine in electrolysis of concentrated sodium chloride
plastics, solvents, water purification
uses for sodium hydroxide in electrolysis of concentrated sodium chloride
soap, detergent, paper, dyes
why is hydrogen used as a fuel
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
overall formula for hydrogen fuel cells
2H2(g) + O2(g) → 2H2O(g)
what is a fuel cell
electrochemical cell that converts chemical energy from fuel into electricity
what happens in process of hydrogen fuel cells
energy is inputted, water electrolysed to produce hydrogen and oxygen both gases captured to be used by fuel cell as energy
outline process of electrolysis of aluminium oxide
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
outline process of electrolysis of dilute sulfuric acid
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
observations of electrolisis of molten lead bromide
silvery solid at the cathode
brown gas at the anode
observations of electrolisis of concentrated aqueous sodium chloride
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
observations of electrolisis of dilute sulfuric acid
colourless gases at both electrodes
cathode gas makes a lighted splint go ‘pop’
anode gas relights a glowing splint
observations of electrolisis of aqueous copper sulfate with copper electrodes
anode becomes smaller, cathode becomes bigger
advantages and disadvatanges of hydrogen fuel cells
advantage- doesnt produce greenhouse gases, sustainable energy creation
disadvatnage- expensive, non efficient, flammable (hazardous)