Welcome to week 4 of science friday. As always, you can check out my previous postings by clicking on the #sciencefriday tag (and changing the filter settings). I apologize for my absence last week; while I love doing this, I had other priorities to attend to. Last week, I talked about the groundbreaking work of Gregor Mendel for the establishment of genetics as a scientific study. This week, I thought I would show the field of chemistry some attention. Today, let’s talk about batteries. These marvels of technology are virtually ubiquitous today: they are in our cars, computers, phones, and even our toothbrushes. But how do they work exactly? Fundamentally, a battery relies on the movement of electrons between two terminals. An electrical potential difference, or [i]voltage[/i], is produced, from which electrons spontaneously move from higher energy (potential) to zero energy. An an apt analogy would be releasing a ball from your grasp. The ball will travel from a higher potential energy state (the air) to a lower potential energy state (the ground). The question becomes what generates this potential? After all, all those circuit problems in physics just attribute the voltage to the battery, but how does the [i]battery[/i] generate a voltage? In the case of the ball example, we can conclude that the ball falling is by virtue of it having mass and the Earth having mass, between which is a gravitational attraction. In the case of the battery, the answer is chemistry. In chemistry, reactions that involve the transfer of electrons are called oxidation-reduction reactions, abbreviated redox for convenience. Oxidation is the chemical process whereby electrons are lost, and reduction is the process whereby electrons are gained. If I place a strip of magnesium metal in a solution of copper nitrate (copper ions and nitrate ions), the magnesium will oxidize to become the magnesium 2+ ion. The two electrons that are lost will be transferred to the copper ions, which will reduce into solid copper metal on the surface of the magnesium strip. This transfer of electrons in the beaker with magnesium and copper ions is uncontrolled. What a battery does is control this transfer to generate voltage from which useful work can be done. The magnesium and copper are separated into two compartments, both of which will be the electrodes of the battery. Since the magnesium is where oxidation occurs (generation of free electrons), it is called the [b]anode[/b] whereas the copper electrode is called the [b]cathode[/b]. These separated compartments are connected by a [i]salt-bridge[/i]. When a wire is connected to the anode and cathode, the electrons released by the magnesium metal travel from the anode to the cathode to generate electric current. The issue is that, almost instantaneously, the current would drop to zero since the cathode would become extremely negatively charged and the anode positively charged, causing electrons to deflect away from the cathode. The salt-bridge remedies this issue by transferring negative ions back into the anode and positive into the cathode while current is running. The voltage associated with a battery is dependent upon the difference in reduction potentials between the two metals involved. In the case of the magnesium and copper, the voltage would be 2.71 V assuming the concentrations of both solutions was 1 M and the temperature of the battery was 25 degrees celsius. Since the production of a voltage is dependent upon a redox reaction, the battery will ultimately drain itself because the reaction has run out of reactants (in our magnesium-copper example, the solid magnesium). Thank you for joining me on another week of science friday. As always, if you have any questions about my post’s content or accuracy, please do not hesitate to ask by commenting. I apologize for the lengthy post, but you can’t explain science thoroughly and briefly at the same time. I will be back next week!