Redox and electrode potential Flashcards
whats a redox reaction
where reduction and oxidation happen simultaneously
whats a half equation
an equation that shows oxidation or reduction - one half of a full redox equation
whats a redox titration
a titration that can be performed to determine how much reducing agent is need exactly to react with a known quantity of oxidising agent, or vice versa
5 steps of calculating concentration of a reagent from a titration
1) write balanced equation or redox reaction
2) decide what you know and what you need to know
3) calculate moles present n=vxc
4) use molar ratios from equation to find moles of other reagent
5) calculate unknown conc c=n/v
state the balanced overall redox titration equation for the oxidation of Fe2+ to Fe3+ by manganate(VII) ions in solution
MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+
state the balanced overall redox titration equation for the oxidation of Zn to Zn2+ by Dichromate(VI) in solution
CrO72- + 14H+ + 3Zn -> 2Cr3+ + 7H2O + 3Zn2+
state the balanced overall redox titration equation for Potassium Manganate(VII) reacted with acidified iron(II) Sulphate
MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+
State the 2 equations that occur when titrating iodine with Sodium Thiosulphate.
1) oxidise iodide ions to iodine
2) titrate iodine solution with sodium thiosulphate
1) IO3- + 5I- + 6H+ -> 3I2 + 3H2O
2) I2 + 2S2O32- -> 2I- + S4O62-
Which way do electrons flow
from more reactive metal to less reactive metal
A metal thats easily oxidised has a very negative or potential electrode potential
negative
whats standard electrode potential
voltage measured understand conditions whena half cell is connected to a standard hydrogen electrode
whats a standard hydrogen electrode
an electrode where hydrogen gas is bubbled through a solution of aqueous H+ ions under standard conditions
what are standard conditions when measuring electrode potentials using the standard hydrogen electrode
- ion solution 1 mol dm-3
- temp 295k (25°C)
- pressure 100kPa
whats an electrochemical series
a list of electrode potentials written in order from most negative to most positive
The more reactive a metal is, the more/less it wants to lose electrons to form a positive ion. (Oxidised)
More reactive metals have more negative/positive electrode potentials.
more
Negative
The less reactive a metal is, the more/less it wants to lose electrons to form a positive ion. (Reduced)
Less reactive metals have more/less positive standard electrode potential
less
More
whats standard cell potential (e.m.f)
voltage between 2 half cells in an electrochemical cell
Whats the formula for E⦵cell
E⦵reduction - E⦵oxidation
How do you know if a reaction is feasible or not
feasible direction of reaction will give positive overall E⦵ value. Reaction will not happen other way round.
what are the 2 problems with predicting reactions
- conditions not always standard, change in temp or conc may change electrode potential
- reaction kinetics not favourable, rate of reaction may be so slow it wont appear to happen. Ea may be too high
How do rechargeable storage cells work
- reactions that occur within them are reversible
- current is supplied to force electrons to flow in the opposite direction around circuit and reverse reactions
- possible because none op the substances escape or are used up
-equations for reactions occurring during recharging are what
same equations for storage cells in reverse
name 2 positive and 2 negatives of electrochemical cells
+cheap to make
+relatively high power density
-production uses toxic chemicals, need to be disposed of at end of lifespan
-chemicals used to make cells=very flamable , dangerous production
whats a fuel cells
device that converts the energy of a fuel into electricity through an oxidation reaction
describe the 4 steps of an acidic hydrogen-oxygen fuel cell
1) at anode, platinum cat splits H2 into H+ and e-
2) PEM only allows H+ across, forces e- to travel around circuit to cathode
3) electric current created in circuit, sued to power something e.g. bike or car
4) at cathode, O2 combines with H+ from anode + e- from circuit to make H2O. This is the only waste product
Whats the PEM
polymer electrolyte membrane
what makes a hydrogen-oxygen fuel cell acidic
H+ ions crossing PEM to balance half-reactions at each electrode makes it an acid fuel cell
whats the overall redox reaction of an acidic + alkaline hydrogen-oxygen fuel cell
1/2O2 + H2 -> H2O
both acidic and alkaline are the same
