C4 electrochemistry Flashcards
define electrolysis
- decomposition of an ionic compound (whether molten or aqueous solution)
- by passage of electric current
what is the anode
positive electrode
what is the cathode
negative electrode
what is an electrolyte
the molten/aqueous substance that undergoes electrolysis
product formed at cathode during electrolysis of lead bromide
lead (silvery solid)
product formed at anode during electrolysis of molten lead bromide
bromine (bubbles of brown gas)
product formed at cathode during electrolysis of aqueous sodium chloride
hydrogen (bubbles of colourless gas)
product formed at anode during electrolysis of aqueous sodium chloride
chlorine (bubbles of pale yellow-green gas)
product formed at cathode during electrolysis of dilute sulfuric acid
hydrogen (bubbles of colourless gas)
product formed at anode during electrolysis of sulfuric acid
oxygen (bubbles of colourless gas)
what happens to electrons in external circuit during electrolysis
- travel thru external circuit
- lost/gained at electrodes
movement of ions in electrolyte during electrolysis
- cations attracted to cathode
- anions attracted to anode
what occurs at cathode during electrolysis
- cations attracted
- gain electrons
- become atoms
what happens at anode during electrolysis
- anions attracted
- lose electrons
- become atoms
what element is formed at cathode
METALS OR HYDROGEN
- if product more reactive than hydrogen, hydrogen formed
- else, product formed
what element is formed at anode
NON-METALS (OTHER THAN HYDROGEN
- if halide present, halide formed
- else, oxygen
observations at cathode during electrolysis of aqueous copper (II) sulfate using carbon (graphite) electrodes
orange-brown copper forms on cathode
observations at anode during electrolysis of aqueous copper (II) sulfate using carbon (graphite) electrodes
bubbles of oxygen are given off
observations at cathode during electrolysis of aqueous copper (II) sulphate using copper electrodes
orange-brown copper forms on cathode
observations at anode during electrolysis of aqueous copper (II) sulfate using copper electrodes
- anode loses mass as copper ions leave it
- sludge forms under anode (impurities in copper)
state the reaction in a hydrogen-oxygen fuel cell
2H2 (g) + O2 (g) –> 2H2O (g)
is the reaction in a hydgrogen-oxygen fuel cell endo or exo
exothermic
what is a hydrogen-oxygen fuel cell
- produce energy
- using hydrogen and oxygen
- water is only chemical product
advantages of using hydrogen-oxygen fuel cells over gasoline / petrol engines
- highly efficient
- renewable
- plentiful cheap supply of reactants
- zero carbon emissions
disadvantages of using hydrogen-oxygen fuel cells over gasoline / petrol engines
- lack of facilities/methods for widespread use
- reactants are gases so must be compressed for storage (hazardous)
- sourcing hydrogen may be expensive/non renewable
