Electrode potentials

What is a half-cell?

contains the chemical species present in a redox half-equation

How can a volatile cell be made?

connecting together 2 different half cells, which then allows electrons to flow

What occurs at the negative electrode? Is it typically on the left or right?

oxidation

more reactive metal

left

What occurs at the positive electrode? Is it typically on the left or right?

reduction (+ve charge attracts electrons)

less reactive metal

right

How do you determine which half-cell will be the positive or negative pole?

the more positive E^o - positive pole

What does a vertical line represent? (metal/metal ion)

the phase boundary between the aqueous solution and the metal

e.g Zn²⁺_(aq) | Zn_(s)

What does a double vertical line represent?

junction between 2 solutions (the salt bridge)

e.g Zn_(s) | Zn²⁺_(aq) || Cu²⁺_(aq) | Cu_(s)

What does the equilibrium in a half-cell look like?

What does a metal/metal ion half-cell contain?

metal rod dipped into a solution of its aqueous metal ion

What does an ion/ion half-cell contain?

ions of the same element in different oxidation states

What is an example of an ion/ion half-cell?

What is used to transport ions in an ion/ion half cell?

inert metal electrode made out of platinum

What is the standard electrode potential? (E^o)

the e.m.f. (of a half-cell) compared with / connected

to a (standard) hydrogen half-cell / (standard)

hydrogen electrode

Temperature of 298 K / 25°C

AND (solution) concentrations of 1 mol dm−3

AND pressure of 100kPa OR 105 Pa OR 1 bar

What are the standard conditions?

solution concentration of 1 mol dm^-3

temperature of 298K

pressure of 100kPa

What does a standard hydrogen electrode look like?

How do you measure a standard electrode potential?

half-cell is connected to a standard hydrogen electrode

electrodes are connected by a wire - allows flow of electrons

solutions connected with a salt bridge - allows flow of IONS

What is an example of a salt bridge?

filter paper soaked in KNO_{3 (aq)}

What does it mean if there’s a more negative E^o value?

greater tendency to lose electrons - undergo oxidation

generally, the greater the reactivity of the metal

What does it mean if there’s a more positive E^o value?

the greater the tendency to gain electrons - undergo reduction

generally, greater reactivity of non-metal

The best oxidising agents have what kind of E^o value?

more positive - them themselves are reduced

The best reducing agents have what kind of E^o value?

more negative

they are oxidised themselves

How do you work out the standard cell potential?

E_cell = E^o(positive electrode) - E^o(negative electrode)

The more positive E value means the equilibrium is shifted where?

to the right

Reduction - Right

The less positive E value means the equilibrium is shifted to where?

the left

oxidation - left