Electricity From Chemicals (1966)

[Music] [Applause] [Music] where does the electricity to run this mixer come from we can follow the wire and see it leads where you might expect to an electric outlet lamps get their electricity in the same way so do some electric trains [Applause] but not everything electrical has to be plugged into an outlet for electricity this portable radio gets electricity from dry cells this flashlight gets electricity from a nickel cadmium battery electricity for starting this automobile engine comes from a lead storage battery a lead storage battery a nickel cadmium battery a dry cell all three produce electricity from chemicals and chemical changes to understand how you have to think about electrons because the story of electricity and chemical changes is really the story of electrons in movement we can learn something about electrons in movement by thinking about ordinary salt a simple chemical compound salt is made of two elements sodium and chlorine to understand what happens when salt is formed let's think of two atoms a sodium atom and a chlorine atom of course this is just a diagram they don't really look like this when sodium chloride forms an electron leaves the sodium atom and becomes part of the chlorine atom the two atoms are changed they're called ions now a sodium ion and a chloride ion now whenever anything gains or loses electrons we say that it becomes charged the sodium ion has a plus or positive charge the chloride ion has a minus or negative charge in a crystal of salt the sodium and chloride ions are arranged something like these marbles frozen in ice chloride ions are larger than sodium ions electrons don't move from ion to ion in crystals of salt but they do in crystals of metals these marbles represent the arrangement of ions in copper we can think of metals as made up of positive ions with negative electrons constantly moving among them let's see what electrons in metals and salt have to do with electricity here we have two strips of metal copper and zinc joined together by copper wires and standing in salt sodium chloride this is an electric cell when the cell produces electricity the meter will show it watch what happens as water is poured into the cell there an electric current has begun to flow through the cell what did the water have to do with it well the salt dissolves in the water we can represent what's happening like this in the crystals of salt the regular arrangement of positive and negative ions is breaking apart some of the molecules of the water have also broken apart in the same way into positive and negative ions in the zinc strip changes begin taking place zinc ions each with a positive charge are leaving the strip of zinc and moving out into the water the electrons that are left behind give the strip of zinc a charge a negative charge the positive zinc ions stay close to the negative strip of zinc you probably know why charges that are alike push away from each other positive charges push apart negative charges push apart but different or unlike charges pull toward each other unlike charges attract each other so the zinc ions which are positive are held close to the strip of zinc which is negative at the same time these positive zinc ions repel other positive ions that come from the salt and the water these ions are pushed away from the strip of zinc some of them are pushed toward the strip of copper and touch it remember electrons are moving through all parts of the copper these electrons can be transferred some of the positive ions that are touching the copper take the exact number of electrons they are missing out of the copper now with the right number of electrons the ions lose their charges and we call them atoms again because the copper is losing electrons it takes on a positive charge so the zinc has a negative charge and the copper a positive charge the two strips are called electrodes and we can see that electricity is being produced why remember the wire is made of the metal copper the wire becomes a path for the extra electrons from the strip of zinc they are pushed out of the electrode and into the wire remember electrons all have negative charges so these electrons from the zinc repel the electrons moving freely through the wire at the same time as you saw before the positive ions around the copper electrode attract electrons this causes electrons to be pulled out of the wire and into the strip of copper so in this electric cell there is a push at the negative electrode and a pull at the positive electrode this push and pull cause billions and billions of electrons in the electrodes and the wire to move in the same general direction and what do we have a flow of electrons an electric current all cells and batteries that produce electricity from chemicals work in this same way now instead of a strip of zinc for an electrode suppose we used a piece shaped like this cylinder and suppose we put the copper electrode inside it with water and salt in the cell will electricity be produced yes this is very much the way dry cells are built even though we call this a dry cell it really isn't dry the chemical inside ammonium chloride is moist like paste the moisture allows the positive and negative ions of the chemical to move freely through all parts of the cell at the negative zinc electrode electrons are pushed into the wire that is attached to it the positive electrode is made of carbon here electrons are pulled out of the wire and are taken up by the ions in the paste dry cells have many uses but dry cells won't produce electricity forever as the chemicals inside the dry cells gain and lose electrons they change that's what's happened to the dry cells in this flashlight their chemicals have changed so much they no longer can produce electricity the cells have lost their charge but there are some electric cells that are designed to be recharged the cells in this flashlight are rechargeable to see why plugging them into an electric outlet recharges them you have to think about electrons in motion again this is a battery made up of rechargeable cells a nickel cadmium battery let's look inside it like the cells we saw before a rechargeable cell has metal electrodes one electrode is made of the metal cadmium when the cell is charged and operating this electrode has a negative charge the other one has a positive charge it's made of a compound that contains the metal nickel the electrodes stand in a moist chemical potassium hydroxide there are positive and negative ions in this chemical as the cell produces electricity the chemicals in it change after a certain number of hours they have changed so much that the flow of electrons stops now remember when the cell was producing electricity electrons flowed out of the negative electrode electricity is made to flow into the negative electrode when the cell is recharged during recharging electrons are also pulled out of the positive electrode into the wire passing an electric current through the cell changes the chemicals in it back to their original form then the cell is charged and it can produce electricity again rechargeable batteries have many uses some even supply enough power to run a small machine like a hedge trimmer or provide power for portable lighting equipment the electrical system of an automobile depends on a lead storage battery which is also rechargeable the electricity produced by the battery is used to start the engine the cells in an automobile storage battery are called wet cells electricity is produced only when the electrodes are immersed in a liquid in this case the liquid is sulfuric acid and water now we can see the separate cells in the battery in each cell just as in the other cells we've seen ions are free to move about each time the battery is used electrons from the negative electrode which is made of lead are pushed into the wire at the same time electrons are pulled out of the wire by the positive electrode which is made of a compound containing lead each time electricity is taken from the battery the chemicals inside it change if the battery is allowed to run down the chemicals change so much that no electricity can be produced a lead storage battery like the nickel cadmium battery can be recharged by passing an electric current through it the electric current changes the chemicals in the battery back to their original form then the chemicals in the lead storage battery can produce electricity again just as chemicals do in nickel cadmium batteries and dry cells electric cells that give us electricity from chemicals bye