IB Chemistry HL Topic 9

Oxidation reaction: The half reaction that involves loss of electrons.
Reduction: The half equation that involves a gain of electrons.

Oxidation numbers should be shown by a sign (+ or –) and a number, for example, +7 for Mn in KMnO4.
Elements which commonly change their oxidation states are carbon, nitrogen, phosphorus, sulfur and the transition metals.

Oxidation numbers in names of compounds are represented by Roman numerals, for example, iron(II) oxide, iron(III) oxide.
The oxidation number, or oxidation state, of an atom is the charge which that atom would have if all covalent bonds were broken so that the more electronegative element kept all the electrons in the bond, hence the sign (+ or –) is always given.

LEORA: loss electrons, oxidation, reducing agentGEROA: gain electrons, reduction, oxidizing agent
Look at oxidation numbers of elements on both sides of chemical equations.

Look at half equations.
These equations are known as half equations and for a redox reaction the half equations for the substance being oxidized and the substance being reduced can be combined in such a way that the electrons cancel out, so as to give a balanced equation for the redox reaction.

H+ and H2O should be used where necessary to balance half-equations in acid solution. The balancing of equations for reactions in alkaline solution will not be assessed.

Oxidising agent: An oxidising agent is itself reduced, that is it is a substance that can accept electrons from another substance or increase the oxidation numbers in another substance. Reducing agent: A reducing agent is itself oxidised, that is it is a substance that can donate electrons to another substance or decrease the oxidation numbers in another substance.

LEORA: loss electrons, oxidation, reducing agentGEROA: gain electrons, reduction, oxidizing agent

Refer to image. Examples include displacement reactions of metals and halogens. Standard electrode potentials will not be assessed.

Students are not expected to recall a specific reactivity series. Reactivity series: A simplified form of a table of standard electrode potentials, this shows the relative reactivities (and spontaneities) of a set of chemicals.

This should include a diagram to show how two half-cells can be connected by a salt bridge. Examples of half-cells are Mg, Zn, Fe and Cu in solutions of their ions.
A Voltaic (Galvanic or electrochemical) cell is a device for converting chemical energy into electrical energy using a spontaneous redox reaction as a source of electrical energy and this is the basis of commercial electrochemical cells (batteries). The opposite, which uses electrical energy to carry out a non-spontaneous redox reaction is known as electrolysis.
The more reactive metal will always be the negative electrode and the greater the difference in reactivity of the metals, the greater the cell potential. A high resistance voltmeter connected between the metals will measure the potential difference between them.

Simple state.

The diagram should include the source of electric current and conductors, positive and negative electrodes, and the electrolyte.
In electrolysis electrical energy is used to bring about a non-spontaneous redox reaction. This is done by passing an electric current through a liquid containing ions, known as an electrolyte. In contrast to metals, the current in electrolytes is carried by the movement of ions rather than the movement of electrons.
Electrolysis: A process in which electrical energy is used to cause a non-spontaneous chemical reaction to occur. Electrolytic cell: The cell in which electrolysis occurs. The cell contains the anode (positive), cathode (negative) and the electrolyte.

State.

He solid conductors inserted into the liquid are called electrodes, the one with a positive charge is called the anode (because it attracts anions) and the one with the negative charge is called the cathode. When the anions reach the anode they lose electrons and are therefore oxidized (LEO). Similarly when the cations reach the cathode they gain electrons and are therefore reduced (GER).