SC10 Flashcards
(16 cards)
What is electrolysis
The decomposition of an electrolyte by passing through a direct electric current
What is an electrolyte?
The [molten ionic compound]/[aqeous solution of an ionic compound] which decomposes when an electric current is passed through
What is electrode?
a conducting rode of metal or graphite
Describe anode cathode, and what/where is the anion and cation located?
Anode is the electrode conected to the positive terminal of the battery, negatively charged ions called anions are attracted to anode
cathode is the electrode connected to the negative terminal of the battery, positiviely charged ions called cations are attracted to the cathode
Describe electrolysis of Molten NaCl
-the start
-at anode
-at cathode
-overall ionic electrolysis equation
(HINT: OIL RIG)
When the powersuppy is turned on the electrodes get charged. The ions in the molten electrolyte get attracted to oppositely charged particles
Cl- ions attracted to the anode
Na+ ions attracted to the cathode
at the anode oxidation takes place
-cl ions lose electrons and get oxidised forming Cl atoms
-Br ions get discharged
-Then two Cl atoms covalently bond to form Cl2 gas
2Cl-(l) > Cl2(g) + 2e-
observation
-bubbles and pale green gas escaping
at the cathode reduction takes place
Na ions get discharged
Na+ ions gain electrons and get reduced to form Na atoms
Na+(l) + e- < Na(l)
Observation
-silvery grey liquid forms at cathode
Overall electrolysis Equation
2NaCl(l) > 2Na(l) + Cl2(g)
Cathode rule for ionic solutions
If +ions(metal) more reactive than hydogen then H*+ ions are discharged more readily than metal ions. Hydrogen is produced at the cathode
(K, Na, Ca, Mg, Zn, Fe)
If +ions(metals) are less reactive than hydrogen then metal ions are discharged more readily than hydrogen ions, metal is produced at cathode
(Cu, Ag, Au)
Anode rule for ionic solutions
If -ions are halogen(Cl, Br,I) then halode ions are discharged more readily than hydroxide ions. Halogen is produced ag anode
If -ions are not halogens( SO4, NO, CO3) hydroxide ions are discharged more readily so oxygen is produced at the anode
What is diff between reactive and inert electrode
Inert electrode is made out of graphite, unreactive so does not affect the electrolysis
Reactive electrode is made out of a material that could react with the solutions such as copper electrode. so affects the electrolysis result
what happens if the anode is made of the same material as the metal ions present in solution?
then the metal atoms from the anode get oxidised and go into the solution as ions
descrivr the electrolysis of sodium chloride solution
ions present in NaCl, and H2O are
Na+ and Cl-, H+ and OH-
When the power supply is switched on H+ and Na+ ions are attracted to the cathode. OH- and Cl- ions are attracted to the anode.
At tje anode
Cl- ions are readily discharged, the Cl- ions lose electrons and get oxidised to Cl atoms.
Two Cl atoms bond covalently forming chlorine gas
2Cl-(aq( + 2Cl(g) + 2e-
OH- remains in the solution
observation
-bubbles
- vapours of green gas near the anode
at the cathode
as hydrogen is less reactive than sodium, H+ ions are discharged, Na+ ions remain in the solution. H+ ions gain electrons and get reduced to H atoms
2H+(aq) + 2e- > H2(g)
observation
- bubbles
overall observation
-colourless solution remaisn colourless
-brown vapours at the anode
-bubbles at the cathode
overall electrolysis
2NaCl(aq) + 2H2O(l) > H2(g) + Cl2(g) + 2NaCl(aq)
electrolysis of Copper(II) Sulphate, using reactive electrode
At the anode
-Cu atoms from the anode lose electrons and get oxidised to Cu2+ ions which go into the solution
Cu > Cu2+ + 2e-
Observation
-anode decreases in size and mass
At the cathode
-cu2+ ions from the solution are attracted to the carhode, cu2+ ions gain electrons and get reduced to cu atoms
Cu2+ + 2e- > Cu(s)
Overall Observation
- blue colour of the solution stays the same
- the concentration of Cu2+ ions in the solution remains constant
-the rate at which Cu2+ ions are formed at the anode is equal to the rate of which Cu2+ ions are discharged at the cathode
Application of electrolysis using copper electrode
Electrolytic refining of copper,
Anode: impure copper
Cathode: pure copper
electrolyre cuso4 solution
What happens to impurities in an electrolyte?
imputities from the anode do not form ions and collect below the anode as a sludge, the anode sludge is xollected as it may contain valuable metallic elements
Describe electrolysis of water(acidified w sulfuric acid)
water is electrolysed in a hofmann voltameter
at the anode
4OH-(aq) > O2(g) + 2H2O(l) + 4e-
at the cThode
2H+(aq) + 2e- > H2(g)
overall equation
2H2O(l) > 2H2(aq) + O2(aq)
Describe electrolysis of water(acidified w sulfuric acid)
water is electrolysed in a hofmann voltameter
at the anode
4OH-(aq) > O2(g) + 2H2O(l) + 4e-
at the cThode
2H+(aq) + 2e- > H2(g)
overall equation
2H2O(l) > 2H2(aq) + O2(aq)
why is the anode replaced from time to time?
anode is made of graphite which is a carbon compound
oxygen is formed at the anode, oxygen reacts with the carbon anode to form CO2 which escapes as gas
The anode wears away so it needs to be replaced
