chemical changes Flashcards
what is reduction?
loss of oxygen, gaining of electrons
what is oxidation?
gain of oxygen, loss of electrons
what is a native metal?
metal found uncombined in the earth eg gold, copper, platinum
what is an ore?
a rock that contains enough metal to make it profitable to extract
how are less reactive metals extracted?
they are reacted with carbon- redox reaction
how are reactive metals extracted?
electrolysis
metal + acid -> ..?
salt + hydrogen
acid + base -> ..?
salt + water
acid + carbonate -> …?
salt + water + co2
what ions are in acids?
H+ ions
what ions are in alkalis?
OH- ions
what is neutral pH?
7
what is acid pH?
less than 7
what is alkaline pH?
more than 7
what happens at the cathode?
positive electrode- reduction occurs
what happens at the anode?
negative electrode- oxidation occurs
why can ionic substances only conduct electricity when molten/dissolved?
the ions are not in fixed positions- they are free to move and carry charge
what forms at the cathode in aqueous electrolysis?
if the metal is MORE reactive than hydrogen, then hydrogen will be produced at the cathode. if the metal is less reactive, then it will form.
what forms at the anode in aqueous electrolysis?
if halides are present then halogens form. if not, oxygen is formed from hydroxide ions in water.
what is the test for hydrogen?
lit splint produces a squeaky pop
what is the test for chlorine?
bleaches damp litmus paper- turns blue to red to white
what is the test for oxygen?
relights a glowing splint
what is the test for carbon dioxide?
turns limewater cloudy
why is electrolysis so expensive as an extraction method?
requires a lot of energy- to melt the compound and produce electrical current
what is cryolite and what is its purpose?
a substance added to aluminium oxide- lowers the melting point so it reduces the energy required
what are the electrodes made of in electrolysis of aluminium?
graphite
why does the anode need regular replacement in aluminium extraction?
oxygen is produced at the anode which reacts with graphite in the anode to form carbon dioxide which wears down the anode
