Electroloysis Flashcards
(32 cards)
what is electrolysis
the decomposition of an electrolyte by an electric current but the compound must be molten or in aqeuous solution
why do ionic compounds only conduct electricity when molten or in aqueous solution
the ions are free to move and carry the charge
why do ionic compounds not conduct electricity when solid
the ions are held in fixed positions in the lattice so cannot move
what are the electrodes made of
graphite/carbon/platinum as these elements are unreactive and do not react with the products of electrolysis
what is the anode
the positive electrode
what is the cathode
the negative electrode
what happens at the cathode
the positive ions are attracted to the cathode and gain electrons and are reduced
what happens at the anode
the negative ions are attracted to the anode and lose electrons and are oxidised
what colour is copper
brown solid
what colour is hydrogen
it is a colourless gas
what colour is oxygen
a colourless gas
what colour is chlorine
a pale green gas
what colour is bromine
a red-brown gas
what colour is copper(II) sulphate solution
blue
how is aluminium extracted
by the electrolysis of a molten mixture of aluminium oxide and cryolite
why is aluminium melted and dissolved in molten cryolite
the mixture has a lower melting point than aluminium oxide as cryolite lowers the temperature required to melt aluminium oxide so reduces the cost of melting aluminium oxide
why do the anodes disappear and have to be replaced frequently
the anodes are made of carbon, so the oxygen reacts with carbon due to the high temperature in the cell to form carbon dioxide which escapes as a gas
what are the reasons for recycling aluminium
it saves energy
natural reserves of bauxite will last longer
there is less mining of the ore
what is produced at the cathode when an aqueous solution is electrolysed
the ions of the less reactive metal otherwise H plus ions
what is produced at the anode when an aqueous solution is electrolysed
halide ions are preferred and discharged in preference to OH- ions but if there are no halides, then OH- ions are preferred
why does hydrogen form at the cathode instead of sodium when an aqueous solution is electrolysed
hydrogen is less reactive than sodium
Hydrogen ions gain electrons more easily than sodium ions
how do you collect and measure the volume of gas produced at the anode
take a graduated test tube, fill it with copper(II) chloride solution and invert it over the electrode
what happens in the electrolysis of sodium chloride solution
hydrogen gas is formed at the negative electrode
chlorine gas is formed at the positive electrode
a solution of sodium hydroxide is formed as the by-product (not the main produce)
what are the uses of hydrogen
in the manufacture of ammonia
in the manufacture of hydrochloric acid
