exam style 1
which one will metal displacement occur?
a) zinc rod dipped in sodium sulfate solution
b) copper rod dipped in cobalt (II) nitrate
c) silver rod dipped in a gold (III) nitrate solution
C
define redox
is a chemical reaction in which the oxidation states of atoms are changed
reduction and oxidation occurs
electron transfer occurs
what is metal displacement ?
solid Metal that wants to take the metal in solution over, must be higher on the table.
Eg. tin will take over Pb because its higher.
what are the standard conditions
100kPa and 25 degrees celcius
what is oxidation and reduction
oxidation is loss of electrons
reduction is gain of elections
how many moles of electrons must be exchanged to oxidise 1 mole of H3PO2 to H3PO4
4 moles
what is the role of the electrolyte (3 points)
complete the circuit
Will allow for the movement of ions
Maintains electrical neutrality in the cell
what is the anode and cathode
anode: where oxidation occurs
cathode: where reduction occurs
3Au+ --> Au3+ + 2Au
which of the following is true for this reaction
a) Au+ disproportionates
b) Au3+ is a reducing agent
c) Au is oxidised
d) none of the above is true
A
what is the charge of the anode and cathode in:
galvanic cell
electrolytic cell
anode is -ve in galvanic cell
cathode is positive in galvanic
opposite charge for electrolytic
which one represents oxidation:
a) Cr2O72- --> CrO42-
b) Mn2+ --> MnO4-
c) NO2 --> NO2-
B
Reasons why EMF is not the same as the theoretical value:
not standard conditions (temp and pressure)
resistance in the wire
eddy currents produced
chemical principles of electrolytical cell:
Utilise an external applied voltage
This drives a non-spontaneous redox reaction to occur
a galvanic cell is set up with Ag (s) and Zn (s)
which is oxidised where will electrons flow?
where would anions flow?
electron flow zinc electrode to the silver electrode
zinc is oxidised
Ag is reduced
anions migrate to the Zn half cell
list 3 potential hazards associated with the electrolysis of molten potassium fluoride
high temp
use of electricity
use of high current flows for good reaction rate
toxic fluorine gas
molten metal
which reaction is NOT a redox
a) 4K + O2 --> 2K2O
b) 2Na + 2H2O --> 2NaOH + H2
c) Li2O + H2O --> 2LiOH
d) 2Na + H2 --> 2NaH
C
what is a fuel cell
It is a device that converts chemical energy into electrical energy via redox
Fuel technology involves the continous supply of reactants to the cells and the continous removal of products
Considered low emission technology
state the role of the half cell in determining the table of Standard Reduction Potentials
hydrogen half cell is the reference half cell
against which the reduction potential of all half cells are measured
Zn and Fe make a galvanic cell
what will be the EMF at 25 degrees?
0.32 V
what are electrochemical cells?
devices which are capable of converting between electrical energy and chemical potential energy
Zn, CO and H2 are all reducing agents. which one of the following explains why:
a) they can all readily donate electrons
b) they are difficult to oxidise
c) none of them can be reduced
d) they all react with oxygen
A
5 points: Advantages of fuel cells over primary/secondary:
Constant flow of reactants , operate for longer if reactants are supplied
Efficiency doesn’t reduce over time
Electrodes dont get depleted during the process of generating electricity
Higher efficiency
Produce constant voltage
state 3 limitations of the Standard reduction potentials table
Eo values depend on conc (1 mol/L)
applied only to aqueous solutions
depends on temperature
E0 values give no indication of reaction rate or Ea
predictive tool - reaction may not actually occur
All gases at 100kPa (standard pressure)
what does the porous membrane do in a battery
completes the circuit and enables the flow of ions
what is the state of an electron
s,l,g,aq
no state