1. The oxidation number of all elements is zero. Eg. The oxidation number of Fe is 0.

2.The oxidation number of an ion in is equal to the individual charge of the ion. Eg. The oxidation number of Zn²⁺ is +2.

A half cell is a device consisting of an electrolyte and an electrode.

Active electrodes are made of the corresponding metal of the salt solution. eg. A Cu²⁺ electrolyte uses a Cu metal electrode.

Passive electrodes do not take part in the reaction and are made of graphite or platinum.

A galvanic cell is a device that converts chemical energy into electrical energy.

It consists of two half cells, the oxidation half cell and reduction half cell.

The electrolyte solutions in the half cells are joined together by a porous barrier or salt bridge which allows the migration of ions.

The electrodes are joined together by an external wire which completes the electrical circuit.

Potassium nitrate, KNO₃

In a galvanic cell the anode is negative.

Reason: The negative terminal is always the source of electrons. Oxidation occurs at the anode which produces an electron flow, so the anode is negative.

Note: In an electrolytic cell (Industrial Chemistry elective) the negative terminal in the DC power supplies the electrons to the cathode which is negative.

A standard reduction table is lists the REDUCTION half equations for numerous chemical species in order of increasing ease of reduction. ie. It is much harder to reduce the chemicals at the top of the table.

Note: If the table is read from RIGHT to LEFT it becomes a standard oxidation table which lists the chemicals species in order of decreasing ease of oxidation. ie. It is much easier to oxidise the chemicals at the top of the table.

Active metals are easily oxidised. The standard reduction table (reading from RIGHT to LEFT) lists metals in order of decreasing ease of oxidation. ie. The most active metals are at the top right of the table. The activity of a metal can be determined by locating its relative position on the right hand side of the standard reduction table. The higher its position on the table the more active the metal is.

An active metal displaces the ion of a less active metal from solution.

Referring to the RIGHT hand of the standard reduction table copper metal is higher than silver metal.

Therefore copper metal is more active than silver metal.

Copper metal will be oxidised (RIGHT TO LEFT of table) and the silver ions will be reduced (LEFT TO RIGHT).

Eo(cell) = 0.76V + 0.80V = 1.56V.

Each cell in the lead acid battery consists of a lead plate and a lead(IV) oxide plate in a sulfuric acid electrolyte.

The lead acid battery contains six cells in series each cell producing about 2 volts generating overall an electrical potential of 12 volts.

1. Electrolyte: 4 to 6M H₂SO₄

2. Anode: Pb

3. Cathode: PbO₂

4. Anode reaction: Pb is oxidised to PbSO₄

5. Cathode reaction: PbO₂ is reduced to PbSO₄

6. Overall reaction:

Pb + PbO₂ + 2H₂SO₄ -discharge→ 2PbSO₄ + 2H₂O

1. Used in electric wheel chairs and mobility scooters. This has greatly improved transport and mobility for aged people.

2. Used as the main start-up battery for cars/trucks replacing cranking. This has greatly reduced the risk of injury in starting a vehicle, reduced the burden on hospitals and increased the quality of life.

3. Used with solar panels to store electrical energy. This greatly increased the quality of life for people who live in isolated communities away from the electrical grid.

The lead and antimony (casings) are toxic to the environment. Soluble forms of these compounds are slowly released to the environment.

They then accumulate in organisms and are biomagnified along the food chain causing serious damage to organisms.

Sulfuric acid from the batteries can also pollute the soil and the surrounding waterways killing aquatic life by lowering the pH.

Aluminium ions also are released from soils that have a low pH and end up in waterways clogging the gills of fish.

The lead acid battery has a high cost due to its large mass.

They are suitable fo high current applications such as automobile starter motors and for storing electricity from solar panels or other devices for homes isolated from the electricity grid.

Their high mass and risk of injury from sulfuric acid excludes their use in portable electrical devices carried by humans.

The lithium anode is coated with the polymer.

The cathode material is formed by a thermal reaction between iodine and the polymer and is poured into the battery.

A thin layer of lithium iodide (Li⁺I^- ) is immediately formed, which becomes the electrolyte of the cell and prevents any further direct reaction between the anode and cathode materials.

The unit is hermetically sealed. All components are non aqueous.

1. Anode: Lithium is oxidised Li(s) → Li⁺ + e^-

2. Cathode: Iodine is reduced ½ I₂(s) + e^- → I^-

3. Electrolyte: A conducting polymer containing Li⁺I^- formed between the anode and the cathode.

4. Overall reaction: Li(s) + 1/2 I₂(s) → LiI(s)

The cell produces a voltage around 3.0 volts and a low current due to the high resistance of the solid electrolyte which limits its use to very low-drain applications such as cardiac pacemakers.

The solid state lithium iodide battery is used in cardiac pacemakers because of its high reliability and long life (10 years).

This has reduced health care costs by reducing the need for replacements and has greatly increased the quality of life of many people.

The battery is also used in some watches.

The convenience of only changing your battery every 10 years is very appealing to a small segment of our societies who have more content and satisfied.

Overall the largest social impact is its use in cardiac pacemakers.

The environmental impact of the solid state lithium iodine battery is minimal due to its small size and relative low numbers of production compared to other batteries.

The polymer containing the lithium iodide is non-polluting as the chemicals are bound within the solid state.

The solid state lithium iodine battery has a higher production cost compared to other batteries.

It is extremely light weight, small and portable. The solid electrolyte has a very high resistance which limits its use to very low current applications.

Note: There are many types of lithium batteries and most are designed to produce larger currents. eg. Lithium batteries for digital cameras and laptop computers. The solid state lithium iodine battery however, is not such a device.