19: Galvanizing Yourself into Electrochemistry in .NET framework

Print GTIN - 13 in .NET framework 19: Galvanizing Yourself into Electrochemistry

Cu(s)

These voltaic cells can t run forever, however The loss of mass at the zinc anode will eventually exhaust the supply of zinc, and the redox reaction won t be able to continue This phenomenon is why most batteries run out over time Rechargeable batteries take advantage of a reverse reaction to resupply the anode, but many redox reactions don t allow for this, so rechargeable batteries must be made of very specific reactants The voltage provided by a battery depends largely on the materials that make up the two electrodes The reactions carried out in the 15V batteries that power your calculator, flashlight, or MP3 player, for example, are often reactions between carbon and zinc-chloride or zinc and manganese-dioxide The high-voltage, long-lived batteries that power your computer, pacemaker, or watch, on the other hand, generally have anodes composed of a lithium compound, which can provide roughly twice the voltage of many other batteries and are longer-lived (certainly a desirable quality in the battery that powers a pacemaker) Although many batteries contain a single voltaic cell, a number of battery types that require high voltages, such as car batteries, harness the power of multiple voltaic cells by wiring them in series with one another A 12V car battery, for example, is created by wiring six 2V voltaic cells together Voltage is measured by attaching a voltmeter to a circuit as shown in Figure 19-1 When the switch is closed, the voltmeter reads the potential difference between the anode and cathode of the cell

A voltaic cell harnesses the reaction 2Al(s) + 3Sn2+(aq) 2Al3+(aq) + 3Sn(s) Which metal makes up the anode and which makes up the cathode The aluminum makes up the anode, and the tin makes up the cathode The best place to start is to add in the spectator electrons to both sides of the equation to balance the positive charges of the cations This gives you the equation 2Al(s) + 3Sn2+(aq) + 6e 2Al3+(aq) + 6e + 3Sn(s) Next, isolate the oxidation and reduction half-reactions (as we explain in 18):

Oxidation half-reaction: 2Al(s) 2Al3+(aq) + 6e Reduction half-reaction: 3Sn2+(aq) + 6e 3Sn(s) Using your an ox and red cat mnemonics, you know that the anode is the site of aluminum (Al) oxidation, while the cathode is the site of tin (Sn) reduction As with the earlier zinc/copper example, this is also apparent using the activity series of metals (see 8), which shows that aluminum is far more reactive than tin

Write the oxidation and the reduction halves of a reaction between cadmium (II) and tin (II) Which makes up the anode and which the cathode How do you know

Sketch a diagram similar to Figure 19-1 of a cell composed of a bar of chromium in a chromium (III) nitrate solution and a bar of silver in a silver (II) nitrate solution if the salt bridge is composed of potassium nitrate Trace the movement of all ions and label the anode and the cathode

In the previous section, we take for granted that charge can flow through the external circuit connecting the two halves of a voltaic cell, but what actually causes this flow of charge The answer lies in a concept called potential energy When a difference in potential energy is established between two locations, an object has a natural tendency to move from an area of higher potential energy to an area of lower potential energy When Wile E Coyote places a large circular boulder at the top of a hill overlooking a road on which he knows his nemesis the Road Runner will soon be traveling, he takes it for granted