chapter 5 electrolysis Flashcards
what does electrolysis mean
splitting up with electricty
process of electrolysis
1) an electric current is passed through an electrolyte (a molten or dissolved ionic compound). the ions move towards the electrodes, where they react and the compound decomposes
2) the positive ions will move towards the cathode (negative electrode) and gain electrons (reduced)
3) the negative ions will more towards the anode (positive electrode) and lose electrons (oxidises)
electrolysis of molten ionic compounds
1)positive metal ions are reduced at the cathode
2) negative non-metal ions are oxidised at the anode
extraction of metals
if a metal is too reactive to be reduced by carbon, then electrolysis is used:
1) aluminium is extracted by the bauxite by electrolysis
2) aluminium oxide has a very high m melting point so its mixed with cryolite to lower its melting point
3) its contains free ions- so it will conduct electricty
4)the positive AI3+ ions are attracted to the negative electrode, where they gain 3 electrons, then sink to the bottom
4) the negative O2- ionis are attracted to the positive electrode, where they lose 2 electrons, and then they combine to form O2 molecules.
electrolysis of aqueous solutions at the cathode
less reactive than hydrogen:
-a solid metal will be produced at the cathode
more reactive than hydrogen
- hydrogen gas will be produced at the cathode
electrolysis of aqueous solutions at the anode
-if OH- or halide ions are present (Cl, Br, I) those molecules will be formed at the anode
-if no halide ions are present then the OH- ions are discharged and oxygen will be formed
why are objects electroplated?
-protect metal beneath from corroding
-make object look more attractive
-increase hardness of the surface and its resistance to scratching
- save money
zinc plating
anode:
Zn (s) –> Zn2+ (aq) +2e-
cathode:
Zn2+ (aq) + 2e- –> Zn (s)
cathode
negative electrode
anode
positive electrode
anions
negatively charged ions
cations
positively charged ions
