OIL = oxidation is loss (electrons, hydrogen), gain oxygen -> occurs at the anode. Positively charged Electrode attracts negative anions
RIG = reduction is gain (electrons hydrogen), loss oxygen -> occurs at the cathode, Negatively charged Electrode attracts positive cations
electrons to flow through a wire or when a flow of electrons makes a redox reaction happen, the processes are referred to as electrochemical changesrusting iron
battery is a term used to describe two or more cells connected together.
what is used as standard?
voltage of a hydrogen half-cell is used as the comparison point in order to give a numerical value to all other standard half-cells
potential of this half-cell is 0.00 V.
H+ ions are in equilibrium.
device that produces electricity as a result of chemical reactions that take place within it, at the surface of the two electrodes.
cathode is positive and the anode is negative
electrons move fr anode to cathode
two half-cells must
be connected, contents of the half-cells not allowed to mix; thus, the two half-cells are usually connected by a porous barrier, or a salt bridge.
porous barrier (or alternatively a salt bridge)
allows the flow of ions to maintain a neutral charge in the half-cells, which prevents the copper (II) ions from coming into direct contact with the zinc electrode
if no flow charge diff develop and reaction stop
- oxidation of zinc
atoms produces a build up of positive zinc ions, Zn2+, in the
positive charge neutralized by negative SO42- ions migrating through the porous barrier towards the anode.
-the reduction of
copper (II) ions to copper atoms reduces the concentration of positive copper
ions in the solution.
resulting negative charge is neutralized by positive zinc ions migrating through the porous barrier towards the cathode
or salt bridge: inverted U-tube filled with an electrolyte solution, w/ open ends of the tube are plugged with a porous material
allows ions to flow in and out of the tube
anode reduced substances becomes oxidized
oxidized substances becomes reduced
half apple rubbed with lemon juice, half not, did not turn brown
lemon juice contains vitamin C, which is highly reactive with oxygen
vitamin C in the lemon juice reacts with oxygen in the air before the fruit can
either a reduction reaction or an oxidation reaction.
indication of the spontaneous direction a redox reaction will take.
higher the Eo, the more the reaction will spontaneously towards the right, favouring a reduction reaction. Occurs at cathode lower the Eo (the more negative), the more the reaction will tend to orient itself spontaneously towards the left, favouring an oxidation reaction
measured in volts (V)
the voltage difference
standard cell potential
maximum electrical potential difference
high reduction potential
higher the reduction potential (Eo), the more the element has a tendency to gain electrons and form negative ions.
- the substance gains electrons easily (electron acceptor)
- the substance is a good oxidant (oxidizing agent)
- the half reaction is a strong reduction reaction
- occurs at the cathode in a galvanic cell
Lower the Eo, the stronger of a reducing agent (reductant) the substance is; it is a good electron donor.
- the substance loses electrons easily (electron donor)
- the substance is a good reductant (reducing agent)
- the half reaction is a strong oxidation reaction
- occurs at the anode in a galvanic cell
reductant (gets oxidized)
oxidant (gets reduced)
Reducing agent /oxidizing agent
Reducing agent – causes the reduction of ANOTHER compound, donates electrons, undergoes oxidation
Oxidizing agent – causes oxidation of ANOTHER compound, accepts electrons, undergoes reduction
number of electrons that must be added/removed cation/anion -> produce a neutral atom
number of zero is given to elements themselves
positive oxidation number
higher the oxidation number, the greater the extent of oxidation.
negative oxidation number
oxidation/reduction in terms o oxidation numbers
Oxidation: "an increase in oxidation number".
Reduction: "a decrease in oxidation number".
oxidation process M → M+ + e– is facilitated by the presence of a suitable electron acceptor
tiny amount of electrolyte on an unprotected metal surface can cause electrons to flow from a higher energy area (anode) to a lower energy area (cathode) initiating and sustaining corrosion
presence of water is necessary in order to transport ions to and from the metal
Corrosion often begins at a location (1) where the metal is under stress (at a bend or weld) or is isolated from the air (where two pieces of metal are joined or under a loosely-adhering paint film.) The metal ions dissolve in the moisture film and the electrons migrate to another location (2) where they are taken up by adepolarizer. Oxygen is the most common depolarizer; the resulting hydroxide ions react with the Fe2+ to form the mixture of hydrous iron oxides known as rust.