redox

when writing equilibria, what side do the electrons go on

left hand side

why is a reference electrode necessary to measure absolute potential difference

because you cant connect the other terminal of the voltmeter directly to the solution, and attaching it to another piece of metal creates its own potential difference

what are the standard conditions

100 kPa gas pressure, 298 K, 1 mol dm-3 concentration of ions in solution

what is the significance of a high resistance voltmeter

to minimzie the flow of electrons between the two half cells, so both reactions remain in equilibrium

what does the sign of a standard electrode potential tell us

the polarity of the electrode compared to the hydrogen electrode (negative means the equilibrium lies further to the left than in the hydrogen electrode); it does not change even if you reverse the reaction

how do you know which element is a better reducing agent

the more negative the standard electrode potential, the better a reducing agent it is

which electrode is the anode

the one where oxidation takes place (the more negative one)

define standard electrode potential

the emf of a cell containing the half-cell connected to the standard hydrogen electrode. standard conditions of 298 K, 100 kPa pressure of gases and solution concentrations of 1 mol/dm3 apply

how do we measure standard electrode potentials of gases

platinum wire, gas bubbled through the solution containing 1 mol/dm3 of the ion

how to measure electrode potential of ions of the same element with different oxidation numbers

the solution should contain one mole/dm3 of each ion, platinum electrode

define absolute potential difference

the potential difference between a metal and a solution of its ions

define electromocitve force (emf)

the measured potential difference of a cell when no current is flowing

how is emf measured

using a high resistance voltmeter

why is a salt bridge used in electrochemical cells

so the ions can flow through

what salt is in the salt bridge

concentrated KNO3

in what direction do electrons flow in an electrochemical cell

from the negative electrode to the positive

what are the rules of using the shorthand convention to represent an electrochemical cell

a solid line indicates a phase boundary (solid to gas for example), the reduced forms of the species are shown on the outside of the diagram, the positive electrode is on the right hand side, double vertical lines represent salt bridge

how to calculate the emf of an electrochemical cell

the difference between the two standard electrode potentials of the half cells, e cell of the right side minus e cell of the left hand side

what is the exception to the cell convention rules

hydrogen electrode always goes on the left