only shows ions that are changing and anything that changes state
the easier it is for a metal to form its positive ion, the more reactive the metal is
the electrolysis of aqueous solutions
A) halogen
B) oxygen
C) hydrogen
D) metal
ionic compound
dissolved in water to form an aqueous solution
in an ionic compound there are 4 types of ions present: 2 ions (from the ionic solution), hydrogen and hydroxide
half equation
shows ions and the movement of electrons
electrons are added to balance the charge
the number of atoms has to be balanced
the small number is always the same as the 2 larger numbers within the equation
electrons are represented by the symbol e-
electrolysis
breaking down an ionic compound, using an electric current
electrolyte: an ionic compound that dissolves in water (making it delocalised) to make a solution that conducts electricity
electrode: where ions lose of gain electrons, depending on their charge (anions lose electrons and cations gain electrons to become neutral)
expensive since lots of energy is needed to melt the solid ionic compound to allow the ions to flow and to produce the electrical current
electrolyte: formed by dissolving an ionic compound and contains hydrogen and hydroxide ions (from the water) and positive and negative ions from the compound
the ions at each electrode gain or lose electrons
when an ionic compound is melted or dissolved in water, the ions are delocalised within the liquid or solution
passing an electric current through electrolytes causes the ions to move to the electrodes
cations (metals) move to the cathode
anions (non metals) move to the anode
electrolysis of aluminium
drawbacks: expensive to extract aluminium from its ore (bauxite)
bauxite is purified to aluminium oxide
aluminium oxide must be melted so that electricity can pass through it and aluminium can be extracted
however aluminium oxide has a high melting point and would be expensive to melt, so instead its dissolved in molten cryolite to lower its melting point
this reduces some of the energy costs involved in extracting aluminium
aluminium forms at the cathode and oxygen is produced at the anode
electrodes
cathode: negative electrode (attracts cations), where reduction happens and if the metal produced at the cathode is less reactive than hydrogen the metal produced
anode: positive electrode (attracts anions), where oxidation happens and oxygen is produced (apart from chloride, bromide or iodide) unless chloride, bromide or iodide are present (in that case they lose electrons and form the corresponding halogen)
anodes (abundant, good conductor and are cheap) are replaced regularly as they burn away as the oxygen reacts with the carbon to form carbon dioxide
oxidation: the loss of electrons and gain of oxygen
reduction: the gain of electrons and loss of oxygen
water dissociates to form hydrogen and hydroxide ions in the electrolyte solution
hydrogen ion: H+
hydroxide ion: OH-
the more reactiveelement stays in solution
the ion of the least reactive element will be discharged