redox Flashcards
what does reduction involve?
- the gaining of electrons
- decrease in oxidation state
oxidation involves…
- the losing of electrons
- increase in oxidation state
disproportionation is when…
the same substance undergoes both oxidation and reduction to form 2 diff products
when assigning oxidation no.s, the most __________ element is assigned the negative oxidation state
electronegative
what is the mnemonic for balancing equations?
use mnemonic
EOHC – ew our hands clashed!
what are the 4 steps to balancing equations for substances in acidic medium?
E – balance Elements that are not O or H
O – balance Oxygen by adding H2O
H – balance Hydrogen by adding H+
C – balance Charge by adding e-
what doe BOD stand for?
biochemical oxygen demand
what is BOD?
the amount of O2 used up by aerobic bacteria to decompose the organic matter in a fixed volume of water over a period of usually 5 days at 293K
what does standard electrode potential mean?
the electromotive force generated by a half cell when measured against the standard hydrogen electrode at standard conditions of 298K, 1 bar of pressure, 1 moldm-3 electrolyte
standard electrode potential is also… (hint: potential)
potential difference
what is a voltaic cell?
a system in which chemical energy is converted to electrical energy through spontaneous redox reactions
what are the components of a voltaic cell?
- voltmeter
- salt bridge
- two half cells
- connecting wires
what is the purpose of the salt bridge?
- maintain /charge neutrality
- completes the electrical circuit
in a voltaic cell, electrons flow from the
anode to the cathode
in a voltaic cell, what happens at the anode?
oxidation
in a voltaic cell at the cathode, the electrolyte undergoes…
reduction
the anode in a voltaic cell is…
-ve
the cathode in a voltaic cell is _____
+ve
all half-cells electrode potential are measured against the ______________________
standard hydrogen electrode
what are the conditions the electrode potentials are measured at?
gases: 100kPa
solutions: 1moldm-3
temp: 298K
the more +ve the Eº value, the more spontaneous the _________ reaction and the __________ the oxidising agent
reduction, stronger
the more -ve the Eº value, the more spontaneous the _________ reaction and the __________ the reducing agent
oxidation, stronger
what is the IUPAC convention for cell notation?
anode|R form|O form|salt bridge|O form|R form|cathode
what mnemonic can we use for cell notation?
EROSORE
Electrode: Anode
Red form
Ox form
Salt bridge
Ox form
Red form
Electrode: Cathode
what is the eq for standard cell potentials?
Eºcell = Eºred - Eºox
what is an electrolytic cell?
a system which converts electrical energy to chemical energy, which drives a non spontaneous reaction
in an electrolytic cell at the anode, the electrolyte undergoes ________ while at the cathode it undergoes _________
oxidation, reduction
in an electrolytic cell, the anode is ______ while the cathode is _______
+ve, -ve
in a voltaic cell, the anode is _____ while the cathode is ________
-ve, +ve
the reaction that occurs in an electrolytic cell at both the cathode and anode has a more _______ Eº value
magnitude
what does Eº measure?
tendency of the forward rxn
what happens to Eº when the conc of an electrolyte (e.g. aq NaCl) is incr in an electrolytic cell?
- high [Cl-] shifts POE to the right
- fwd rxn is favoured
- causes Eº to become more (+)ve (Eº measures tendency of forward rxn)
- high [Na+] shifts POE to the right
- fwd rxn is favoured
- Eº becomes more (-)ve however it is still less than water
when Eºox becomes more (+)ve, how does this change the value of Eºcell?
causes Eºcell to increase in magnitude
what is the eqn for current, electricity and time
Q = I x t
Q= amt of electricity/C
I= strength of current/A
t= time/s
what is the eqn to find the amount of product formed in the electrolytic process?
Q = ne x F
Q= amt of current/C
ne= no. moles of e- transferred
F= Faraday’s constant
in electroplating, the object being electroplated is placed at the…
cathode
does SO4^2- get reduced or oxidised?
it does not get oxidised or reduced
___ always gets reduced and ____ always gets oxidised
Cu, Br
