Electrolysis Flashcards
Where do cations and anions move to when a direct current is passed through the electrolyte?
Cations attracted to negative electrode (cathode) and anions attracted to positive c electrode (anode)
What discharge at cathode and anode
Cations discharged at cathode (metals and hydrogen gas)
Anions discharge at anode (non metals
What do they mean by discharging of an ion
It is the loss of charge of ions, which cause formation of products at cathode and anode
Whats electrolysis
thermal decomposition of the compound by driving a direct current throught the molten cmpd or soln of the compd
Whats battery for in electroolysis
Drive flow of electrons in electrolytic setup
Where does electron flow in fuel cell
The electrons flow from a more reactive metal electrode to a less reactive metal electrode
The ____ the two metal electrodes in the reactivity series, the greater the voltage of electric cell
further
What will be observed over time for two metal electrodes?
More reactive metal become smaller over time as it was oxidised and less reactive metal become “larger” as electrolyte gets reduced and form atoms on the surface of the less reactive metal
WHats a fuel cell
a device which uses a fuel to react with oxygen in air to produce electrical energy directly
Give the hydrogen cell equation at:
Anode electrode
Cathode electrode
overall cell equation
Anode elect: 2H2 –> 4H+ + 4e
Cathode elect: O2 + 4H+ + 4e –> 2H2O
overall: 2H2 + O2 –> 2H2O
When wire connected between copper electrode and iron electrode, in an eelctrolyte, effervescence seen on copper electrode Why?
State half eqn at iron electrode and copper electrode
Iron is a more metal than copper. Iron underggo oxidation and lose electrons. The electrons flow from iron to the copper electrode thru wire and into electrolyte, reducing H+ ions to hydrogen gas, and thus effervescence seen on copper electrode.
Copper elect: 2H+ + 2e- –> H2
Iron elect: FE –> Fe2+ +2e-
Define electrolysis
the conduction of electricity by an ionic compound (electrolyte), when molten or dissolved
in water, leading to the decomposition of the electrolyte
why can electrolyte only conduct electricity when in molten state or in soln
current is carried as a result of movement of ions to electrodes
Why cant a non electrolyte condct electricity
cant ionise
During electrolysis of PbBr2 what happens?
Pb2+ gather around cathode to undergo reduction, metallic lead produced
Br- gather around anode to undergo oxidation. Bromine is formed
For electrolysis of PbBr2, Anode half eqn cathode half eqn Overall chem eqn Ionic eqn
Anode: 2Br- –> Br2 + 2e-
Cathode: Pb2+ + 2e- –> Pb
Overall: PbBr2 –> PB + Br2
Ionic: Pb2+ + 2Br- –> Pb + Br2
Why there more than two types of ions in aqueous electroltye
water ionises to give hydrogen ions and hydroxide ions
In electroplating, the object to be plated is the ________ and the metal used for plating is the _______________
cathode
anode
In electroplating, the electrolyte is ____
a salt soln containing cations of metal that made anode
Cations in electrochemical series (Increasing preferential discharge)
K+ Ca Na Mg Al Zn Fe Sn Pb H Cu Ag Au
Anions electrochemical series (increasing preferential discharge)
F SO4 NO3 Cl Br I OH
When Na+ and H+ present, which is more prefentially discharged
H+ ions gain electrons more readily than Na+ ions and thus H+ is more preferentially discharged
when So4 2- and OH- present, which more preferentially discharged
OH- lose electrons more readily than SO4 2- ions, thus OH- is preferentiallyA discharged
In a dilute sodium chloride as electrolyte, what is the product at cathode? [ions present: Na+, Cl-, H+ and OH-). WHY?
hydrogen. based on electrochemical series, H+ gain electrons more readily than Na+, thus H+ is more readily reduced: 2H+ + 2e- –> H2
In a dilute sodium chloride as electrolyte, what is the product at anode? [ions present: Na+, Cl-, H+ and OH-). WHY?
oxygen. Based on electrochemical series, OH- ions loses electrons more readily than Cl-, thus OH- is perefentially oxidised: 4OH- –> O2 + 2H2O +4e-
In a concentrated sodium chloride as electrolyte, what is the product at anode? [ions present: Na+, Cl-, H+ and OH-). WHY?
chlorine, The conc of Cl- is high enough for the conc effect to take place, due to closeness of position of Cl- and OH- in electrochemical series. Thus Cl- is preferentially oxidized.
2Cl- –> Cl2 +2e-
In a concentrated sodium chloride as electrolyte, what is the product at cathode? [ions present: Na+, Cl-, H+ and OH-). WHY?
hydrogen. Although conc of Na+ is high, distance between positions of Na+ and H+ in electrochemical series is too great, hence H+ is still preferentially reduced 2H+ + 2e- –> H2
what are the two active electrodes
copper and silver
The more/less reactive metal ion discharge
less
What happens at the copper anode in an electrolyte
Instead of OH- losing electrons, Cu atoms of anode lose electrons, thus copper anod dissolves:
Cu –> Cu2+ + 2e-
why was is necessary to acidify water before electrolysis
Water is poor electrical conductor, Adding acid increase its conductivity by increasing conc of free mobile ions
In practice, vol of oxygen gas collected is lesser than half of hydrogen collected (exactly half is expected). Why
Oxygen more soluble than hydrogen. both oxygen and hydrogen dissolve in soln but more oxygen dissolve. thus vol of oxygen collected lass than expected
describe purification of metal (refine impure copper) with copper ii sulfate as electrolyte
place copper electrode as anode and pure copper as cathode. During electrolysis, the copper atoms of anode oxidise and lose electrons and Copper II ions dissolve in electrolyte. these copper ii ions migrate to cathode, gain electrons and form back as copper atoms.
Anode bcecome smaller and smaller and cathode becomes bigger
eventually impurities like other metals will ffall off to collect below anode
cocnetration of electrolyte unchanged
Describe process of electroplation
During electrolysis, anode dissolves and ions thus produced migrate to cathode where they are discharged and deposited as a layer on object. conc of electrolyte remain constant
What happenes when u want electroplate non conducting material
Spray with metallic pain or coat with graphite powder
During electroplation, sodium ions reduced to form sodium atoms. Write a eqn
Na+ (aq) + e- –> Na (s)
