Incidentally...

Car batteries have plates of lead and lead dioxide, with sulphuric acid between them. There are usually six cells together to make a 12 volt battery. This battery is heavy and full of acid but can produce huge electric currents for long periods of time. It works well even if it is very cold, does not foul up and can be recharged. Recharging means that the chemical reactions which occur while the battery is in use (both plates change to lead sulphate as the car battery drives a current) can be reversed by passing a reverse electric current, from the car's generator, through the battery.

 
   
Did you know?

The original "dry" batteries had a damp paste of ammonium chloride (a salt, this time) between a zinc plate, usually the battery container, and a carbon rod. (Carbon conducts electricity, so can be used instead of a metal.) A paste is a lot more convenient than a liquid for portable batteries. You can still buy them - they are a lot cheaper than more modern designs.

Many commercial batteries have a name which gives an indication of their chemical structure, either of the plates or the paste in between. e.g. Mercury cells, Lithium cells, NiCad batteries (which have Nickel and Cadmium plates), Alkaline batteries have an alkali, potassium hydroxide paste, between the plates (in fact most modern batteries are "alkaline").

Car batteries have plates of lead and lead oxide, with sulphuric acid between them. There are usually six cells together to make a 12 volt battery. This battery is heavy and full of acid but can produce huge electric currents for long periods of time. It works well even if it is very cold, does not foul up and can be recharged. Recharging means that the chemical reactions which occur while the battery is in use can be reversed by passing a reverse electric current (from the car's generator) through the battery.

 
   
History

Electrochemistry started in 1786 with the discovery by the anatomist, Galvani, that a dead frog's leg would twitch when touched by two different metals at the same time! His fellow Italian, Volta, replaced the frog's leg with salty water and produced the first chemical cell which would drive an electric current in 1800. Mr. Volta used silver and zinc discs separated by a cloth soaked in salt solution. He stacked them in a pile to make a battery with a high voltage! A battery is called a pila in Italy, and means a set of electric cells.

Volta tried all the metals he could lay his hands on, touching them in pairs on his tongue and estimating the electrical effect by the unpleasantness of the sensation! He was thus able to arrange the metals in an electrochemical series, according to how much voltage they produced when separated by an acid or salt solution. Cells work by chemical reactions between the metals and the conducting liquid (electrolyte) where they are in contact. The reactions only occur when electrons (the bits of atoms responsible for their chemical behaviour) are conveyed from one metal to the other. The metals must be connected somehow for the electrons to get from one to the other, and it is this flow of electrons which is the useful electric current.

Michael Faraday advanced our knowledge of electrochemistry enormously in the 1840s. Look on the back of a £20 note to see a picture of him and a list of electrochemical terms he introduced. You can also see a picture there of an electromagnetic generator he invented, which then took over from batteries as the most important way of making electric currents flow! Designing successful electric cells is a difficult business - people have been trying to improve them for the past 200 years. There are now rechargeable cells, where the chemical reactions can be reversed by passing an electric current from somewhere else through the cell, making it ready to work again. There are also fuel cells which convert fuels and oxygen into electricity without burning them together. What we haven't produced yet is a battery which is light enough and powerful enough to run an electric car as far as a tank of petrol will. There is a fortune to be made by the person who manages it!

 
   
Things you can try yourself

First, the one you would wish to avoid! If you have any metal fillings in your teeth, avoid making tooth contact with any different metal! If you accidentally touch a bit of aluminium foil, say, with the filling, the two metals and your body fluids, saliva and blood, will send a small, but unpleasant electric current through the tooth and jangle its nerves.

This one is a bit more controlled. Use a copper coin, a bit of aluminium foil and the saliva on your tongue to make a "battery". The coin and foil touch one another away from your tongue, and touch your tongue in separate places. You will experience a very sharp taste at the coppery end when the electric current flows!

 

 

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