Redox and Electrode Potentials Flashcards
What are the steps to construct redox equations
Write half equations
Balance hydrogens
Balance electrons
Form full equation - electrons cancel out
What are the two common redox titrations you need to know
Potassium manganate (VII) (KMnO4(aq)) under acidic conditions
Sodium thiosulfate (Na2S2O3(aq)) for determination of iodine (I2(aq))
What are the examples of manganate(VII) titrations
Iron(II) ions (Fe2+)
Ethanedioic acid (COOH)2
In iodine/ thiosulfate titrations what is oxidised and what is reduced
What are the 2 half and overall equations
Thiosulfate are oxidised
Iodine is reduced
Oxidation: 2S2O3^2-(aq) -> S4O6^2- + 2e-
Reduction: I2(aq) + 2e- -> 2I-(aq) + S4O6^2-
Overall: 2S2O3^2- + I2(aq) -> 2I-(aq) + S4O6^2-(aq)
What is a voltaic cell
A type of electrochemical cell that converts chemical energy into electrical energy
What are half-cells
Half cells contain chemical species present in a redox half-equation
How can you make a voltaic cell
By connecting together two different half cells which allows electrons to flow
What are the two types of half cells
Metal/ metal ion
Ion/ ion
How do you know which electrode has a greater tendency to gain or lose electrons
In a cell with two metal/metal ion half cells connected, the more reactive metal releases electrons more readily and is oxidised
Operating cell
- electrode with more reactive metal loses electrons - is oxidised Operating cell- negative electrode
- the electrode with the less rreactive metal gains electrons and is reduced - positive electrode
Define standard electrode potential
The tendency to be reduced and gain electrons
With standard conditions -
- solutions have a concentration of exactly 1 moldm-3
- temperature is 298K
- pressure is 100kPa (1bar)
How do you measure standard electrode potential
Half-cell connected to a standard hydrogen electrode
- the two electrodes are connected by a wire to allow a controlled flow of electrons
- the two solutions are connected with a salt-bridge which allows ions to flow. The salt bridge typically contains a concentrated electrolyte solution that does not react with either solution
If an electrode potential is more negative:
- the greater the tendency to lose electrons and undergo oxidation
- the less the tendency to gain electrons and undergo reduction
The more positive the electrode potential:
- the greater the tendency to gain electrons and undergo reduction
- the less the tendency to lose electrons and undergo oxidation
How do you calculate standard cell potential from standard electrode potentials
Cell potential = positive electrode potential - negative electrode potential
How do you construct overall equations from half equations
The redox system with more positive electrode potential will react from left to right - gain electrons
System with more negative will react from right to left - lose electrons
Reduction half equation is same way around
Oxidation half equation is reversed
What effect does cis-platin have on bacteria
Binds with DNA and stops replication
What angle do two identical ligands need to be a trans-isomer
180 degrees
Define ligand substitution
When a ligand in a complex ion is replaced with another ligand
What ligand substitutions do we need to know
[Cu(HO)6]2+ with NH3
[Cu(H2O)6]2+ with HCl
[Cr(H2O)6]3+ with NH3
Cu2+ ammonia reaction
Copper sulfate forms pale blue octahedral complex ion [Cu(H2O)6]2+
Ammonia is acting as a base and forms the pale blue precipitate
What is the overall equation for Cu2+ ammonia reaction
[Cu(H2O)6]2+ + 4 NHH3 —> [Cu(NH3)4(H2O)2]22+. + 4 H2O
What is the result of the Cu2+ chloride reaction
Yellow [CuCl4]2- complex ion forms
Chlorides are larger than H2O so can fit around the Cu2+
The solution appears green when there is an equal amount of each complex ion (yellow and blue)
What is the Cu2+ chloride reaction equation
[Cu(H2O)6]2+ + 4 Cl- <—> [CuCl4]2- + 6 H2O
Results for the Cr3+ ammonia reaction
What happens when you add excess ammonia
Grey green precipitate of Cr(OH)3] + 3NH4+
Excess ammonia dissolves the precipitate to form the dark purple complex ion [Cr(NH3)6]3+
