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Electrochemical Cells

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This video shows how a typical electrochemical cell is setup and works. It shows the standard hydrogen half-cell at about 16:00 minutes.

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this is a production what's the chemical education material study the electricity is a moving force in our lives one of the great advantages of electricity is the ease with which it can be stored in small even tiny containers called electrochemical cells each cell contains only two electrodes and a chemical electrolyte  when two or more cells are used they are called a battery car batteries contain 326 cells that is 6 or 12 electrodes electrochemical cells provide current and voltage which can accomplish a great variety of tasks what is on inside an electrochemical cell in your laboratory experiments you may have constructed tricks similar to this one two beakers containing Metal Sheets and ionic Solutions are connected by this YouTube filled with an electrolyte aqueous sodium nitrate  we complete the external circuit between a copper electrode and one finger and a zinc electrode the other Beaker and electric potential is recorded as voltage  removing the YouTube breaks the circuit does zero reading on a voltmeter shows the cell is no longer operating  only a complete a circuit turn the lights out as well as external Through the Wire allows an electric cell to operate let's examine another electrochemical cell arranged for easy observation which Heights so you can see changes which occur reimburse the two electrodes one electrode is copper it is immersed in an aqueous solution of sodium nitrate II electrode is silver aqueous solution of silver sulfate  complaining this cell is a porous barrier if prevent mixing Bud Light YouTube in the previous valve permits ion to penetrate constructed an electrochemical cell does it generate an electric potential it does in fact almost pair of electrodes any electrolytes will generate a potential but what chemical reactions led to a potential this cell  we have copper and silver electrodes immersed in electrolytes  the solutions are kept from by the forest barrier on the left there are positive sodium ion and negative nitrate ions and on the right positive volume and negative sulfate ions all the ions are in random thermal motion  the barrier prevents the mixing of the tooth although we can't see them reactions are taking place at each electrode look at what happens when copper is placed into the solution initially copper atoms nitrate ions and sodium ions are present set up the surface copper atoms can give up to electrons be oxidized and enter the surrounding solution as copper ions what's electrons give the electrode negative charge some of the copper ions in turn can strike the copper game two electrons reduce the solid copper at equilibrium a negative charge has accumulated on the copper electrode as a result only a minut amount of aqueous copper ions are present at equilibrium  the equilibrium half-reaction involve solid copper aqueous copper ions at electrons now let's look at the similar equilibrium reaction at the silver hear the positive silver ions of the silver sulfate solution the silver electrode and adhere Optimum silver ion takes up an electron to become silver metal simultaneously a different silver atom can lose an electron to form a silver ion we can express equilibrium by this half equations silver ions aqueous plus electrons in equilibrium with silver solid only am I news amount of reaction occurs because of the accumulated charge at the electrode before the circuit is closed exists at each electrode different amounts of charge have accumulated at each electrode since the metals as well as the electrolytes are different the copper electrode has become more negative than the silver what will happen when we connect the electrodes directly settle in find out we close the circuit by connecting the two electrodes with a conducting wire time lapse photography compresses 12 hours into a few seconds the copper side of the cell gradually turns blue crystals grow on a silver electrode now what's the proper electrode process once more you might guess it's a blue color appearing around the copper electrode comes from aqueous copper ions Shepherd analysis confirms this oxidation of copper atoms to Copper ions and darkens the surface  the electrode Atwood oxidation occurs is called the anode  the oxidation half reaction is copper solid gives copper ion aqueous plus two electrons  now look at how the silver Electro changes after the external wire is connected receive still in time lapse photography shiny metallic needles growing from the surface of the electrode Alice's needles are metallic silver and that the electrode is gaining mass  reduction of silver ion to Silver is occurring  the electrode at which reduction occurs is called the cathode the reduction half-reaction is silver ion aqueous plus one electron gives silver solid here is the complete cell oxidation Copper at the anode freeze electrons which flow to the external circuit to the cathode for ions accept electrons and are reduced to black silver  deposit of copper ions are now distributed throughout the last compar copper ions pass through the barrier into the other compartment let's check the barrier material first we played some aqueous copper sulfate on a piece of the barrier penetration is slow but in a little while diffusion occurs the barrier is Horus test for copper ions is the blue color they form with aqueous ammonia when the solution from the cathode compartment is also tested a pink blue color form even though the barrier was designed to minimize mixing some positive copper ions have moved through the barrier from the loud toward the cathode have positive silver ions moved through the porous barrier in the opposite direction when the solution from the castle inside of the cell is added to aqueous sodium chloride precipitate of silver chloride formed as expected using this will check for silver sounds on the left side of the barrier no precipitate forms within the accuracy of this no positive silver ions have moved toward the anode silver ions have remained in the cathode compartment the barrier has prevented General mixing  we have now seen that the copper ions move through the barrier the right half of the cell and that the silver ions do not move through the barrier to the left but what about the negative sulfate ions which were Finley in the right half of the cell do they move across the barrier let's check the motion of the negative ions if we mix sulfate ions those in the cathode half of the cell with aqueous barium ion we obtain a white precipitate barium sulfate what will test for sulfate ions in the other half of the cell a precipitate formed indicating that negative sulfate ion did move toward the anode from the cathode compartment  so you the copper and silver ions tend to move toward the cathode so do all positive ions while negative ions such as tend to move toward the anode we have also observed that copper is oxidized to Copper ions around the anode and ions are reduced to metallic silver at the cathode how can we account for all these observations you may remember that prior to the closing of the circuit there was a difference in potential between the anode and the cathode  closing the circuit provides are the electrons to flow from the copper anode to the silver cathode  at the Copper electrode copper ions require electrons if they are to form atoms of copper metal  this reaction becomes less frequent as electrons Flow Away in the external fewer electrons are available in the metal however proper Adams continue to give up electrons the net formation of copper ions then migrate away from the anode  so closing the circuit upsets the original equilibrium simultaneously at the silver cathode and electrons make the reduction of silver ions more likely the electrons supplied from the copper anode make it more likely that silver ions will be reduced silver medal the previous tendency of the silver metal to lose electrons back to the electrode is now over balanced by the tendency of the ions to require the in flowing equilibrium no longer exist give me the net reduction of the positive ions to Silver metal the total effect produces movement of positive ions in solution toward the cathode have negative ions anode and a flow of electrons Through the Wire from the anode to the cathode the true in every electric cell after the cell has operated for a long time the potential drops to zero the cell is dead there is no longer any Net10 for electrons to move between the electrodes why is it initially before the circuit was closed the electrodes were a can sodium nitrate and silver sulfate respectively the silver sulfate solution provided a large number of silver ions these ions react at the metal surface but equilibrium is maintained only a very small number of copper ions are provided by the Librium reaction at the Copper electrode when the circuit is closed equal reham is upset there is a net oxidation of copper and reduction of silver the positive ions undergoing netmotion where did the cathode of copper ions increases the concentration of silver ions decreases some small concentration of silver and some large concentration of copper no further net reaction will occur an equilibrium when is New equilibrium there is no net tendency for electrons to flow from one electrode to another that is why the the cell is zero that we see that as the ionic concentrations change the voltage drops toward zero not all cells involves simple oxidation and reduction of solid electrodes this cell uses gaseous hydrogen at one of the this cell has a potential of about 1 volt  again one electrode is silver in a solution of silver sulfate set an electrode is the relatively inert metal over which hydrogen gas is bubbled the rough black Platinum is used to bring electrons into electrical contact with a gas on the solution the solution in Diamond sodium hydroxide study the cell reaction we will use broom final blue indicator let's check the indicators color as the city varies what is yellow in acidic Solutions intermediate colors neutral solution we add the indicator around the hydrogen electrode  the blue color indicates that the solution is base now we disconnect the voltmeter and complete the circuit with conducting wire what's the indicator around the hydrogen electrode as the cell operates solution which was basic before the circuit was closed is now showing that as the cell operates hydrogen ions are forming here are the standard tubes to confirm this the equation for the half reaction at the Platinum electrode must be hydrogen gas gives two electrons plus two hydrogen ions aqueous  at the silver electrode the half-reaction is silver ions aqueous plus one electron gives silver solid that will disconnect the shell and measure the potential again we would expect the operation of the cell to have decreased the cell Potential from earlier value of about 1 volt yes the present value is only eight tenths of of old normal operation lower the cell potential what would happen if we know further decrease the concentration of silver ions addition of an Quia sulfide solution will do the trick by converting much of the aqueous silver ion to insoluable H2S  what's the voltmeter add sulfide ion  the song Potential shifts as the silver ion concentration decreases  the needle moves to the opposite side the scale zero let's check this experimental 8 by observing Primal once more we disconnected wake me the electrodes directly to each other now watch the indicator color the change from yell go to Blue indicates the hydrogen ion concentration is decreasing  hydrogen gas is now being formed by the reduction of hydrogen ions the electron flow has reversed this electrode is now the cathode the solution becomes basic as the comparison tubes reminder  give me the Mitchell setup hydrogen gas reduced silver ions present in large concentrations to produce hydrogen ions and silver metal  but when the concentration of silver ions was decreased by addition of sulfide the net reaction reversed metallic silver then reduced hydrogen ions to produce silver ions said hydrogen gas  so the potential of a cell and even the direction of current flow are highly sensitive to the concert the reactants but at constant concentration the potential is constant working at concentration allows us to measure voltage is known as zero values for example an easy row potential of 0 volt is arbitrarily assigned this half reaction producing H2 gas at one atmosphere pressure from one molar aqueous hydrogen ion value serves as a comparison with potentials of concentrations of other substances at standard temperatures ZZ zero values may be combined to predict unknown potentials and hence the tendency of electrochemical reactions to occur positive values for any reaction the reaction is spontaneous further studies such as ours would shows up all electrochemical cells operate similar fashion  the positive ions move toward the cathode the negative ions toward the end simultaneously there is an external flow of electrons from the anode to the cathode there is oxidation at the anode reduction the cathode inside every electrochemical cell  the flowing electrons driven by the cell half-reaction provide those power without your life would be quite change perhaps you would like to discuss what is happening in this experiment

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