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OIL RIG
- 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
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electrochemical changes
- 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
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Galvanic Cell
battery is a term used to describe two or more cells connected together.
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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.
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Voltaic Cell
- galvanic cell
- 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
- zinc half-cell,
- - oxidation of zinc
- atoms produces a build up of positive zinc ions, Zn2+, in the
- solution.
- positive charge neutralized by negative SO42- ions migrating through the porous barrier towards the anode.
- copper half-cell,
- -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
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Electrochemical cells
- anode reduced substances becomes oxidized
- oxidized substances becomes reduced
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redox reactions
- 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
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half-reaction
either a reduction reaction or an oxidation reaction.
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Reduction Potential
- 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
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Electric potential
- measured in volts (V)
- the voltage difference
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standard cell potential
maximum electrical potential difference
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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
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lower Eo?
- 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
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reductant/oidant
- reductant (gets oxidized)
- oxidant (gets reduced)
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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
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oxidation number
- number of electrons that must be added/removed cation/anion -> produce a neutral atom
- number of zero is given to elements themselves
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positive oxidation number
higher the oxidation number, the greater the extent of oxidation.
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negative oxidation number
reduced state.
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oxidation/reduction in terms o oxidation numbers
- Oxidation: "an increase in oxidation number".
- Reduction: "a decrease in oxidation number".
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corrosion
- 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.
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