4 Electrolysis
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Define electrolysis
the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
anode
positive electrode
cathode
negative electrode
electrolyte
the molten or aqueous substance that undergoes electrolysis
products formed at the electrodes made during the electrolysis of molten lead(II) bromide
Cathode: the lead forms Anode: the bromine forms
products formed at the electrodes made during the electrolysis of concentrated aqueous sodium chloride
Cathode: hydrogen gas forms Anode: chlorine gas forms
products formed at the electrodes made during the elctrolysis of dilute sulfuric acid
Cathode: hydrogen gas Anode: oxygen gas forms
what’s substance is formed at the cathode?
metals or hydrogen
what’s formed at the anode?
non-metals
why are metal objects electroplated?
to improve their appearance and resistance to corrosion
Electroplating
putting a thin layer of a metal onto a metal object via electrolysis
to carry out electroplating: (electrodes and electrolyte)
• the cathode is the object to be plated • the anode is the plating metal • the electrolyte contains ions of the plating metal
At the cathode which substance will form a product?
The least reactive one
At the anode which substance will form a product?
the halide or if theres no halide then oxygen. unless the concentration of the halide is very low.
describe the electrolysis of aqueous copper(II) sulfate using inert electrodes
at anode: oxygen gas forms (bubbles form) and the oxygen reacts with carbon eletrode to form carbon dioxide at cathode: copper forms (accumilating on its exterior)
describe the electrolysis of aqueous copper(II) sulfate using copper electrodes
at anode: copper gets oxidised to form copper ions at cathode: copper ions gets reduced to form solid copper the eletrolyte doesn’t change concentration because Cu electrode is oxidised to form Cu ion and Cu ion is reduced at cathode
Hydrogen-fuel cells
uses hydrogen and oxygen to produce electricity with water as its only product
advantages of hydrogen fuel cells in comparison to gasoline
No vehicle emissions other than water vapor. Fuel economy equivalent to about twice that of gasoline vehicles. Hydrogen is abundant, and can be made from renewable energy.
Disadvantages of hydrogen fuel cells
Expensive. Acceptable range requires extremely-high-pressure, on-board hydrogen storage. Few places to refuel. Lack of infrastructure to support the distribution of hydrogen. Currently hydrogen fuel is made from nonrenewable natural gas in a process that creates enormous CO2 emissions.