Background

What is an electrochemical cell?
You can think of an electrochemical cell as an energy converter. The cell takes chemical potential energy and turns it into electrical energy. An electrochemical cell uses a chemical reaction to create and store electrical charge. A cell always consists of two electrodes and an electrolyte that acts chemically on at least one of the electrodes.

What is electric current?
Electric current is the flow of electric charge that transports energy from one place to another. Electric charge flows through a circuit because of an applied voltage across the circuit. The current is defined as the amount of electrical charge that flows past a point in a given amount of time (usually one second).

Subatomic Particles and their Characteristics
All atoms consist of three types of particles: protons, electrons, and neutrons. Protons have a mass of about 1 a.m.u. (which is pretty small) and have a positive charge. Neutrons have no net charge and also have a mass of about 1 amu. Electrons, on the other hand, have a much smaller mass (only about 1/1800 of that of a proton or neutron) and a negative charge.

What is an ion?
All atoms have an equal number of positively and negatively charged particles. This means that all atoms have no net charge, that is, atoms are neutral. Sometimes an atom may gain or lose an electron or electrons. Any atom that has gained or lost an electron now has a net charge. These charged species are called ions. Positive ions, called cations, have more positively charged particles (protons) than negatively charged ones (electrons). Anions (negatively charge ions) have more electrons than protons.

Common metals and their characteristics
A majority of the elements on the periodic table are metals. Most metals exist in the solid phase. Can you think of some common metals? How about aluminum, copper, and tin? You got the idea. Let's look at copper as an example of a common metal. First, a piece of pure copper would consist of only one type of atom. All copper atoms are neutral, meaning the atoms have the same number of positively charged particles (protons) as they have negative ones (electrons). But copper's electrons (like most metals) are not "locked" in place, stuck with one copper atom. Instead, the electrons roam from one atom to the next with a freedom of movement. This freedom of the electrons' motion provides a number of metals' useful properties, including being good conductors of heat and electricity.

What is a salt bridge?
A salt bridge is a part of an electrochemical cell. The bridge allows ions to freely move from one part of the cell to the other part. This keeps the electrons flowing freely between the two cell parts. Without the salt bridge, a charge would quickly build up in the solution and reduce or stop the movement of electrons.

What is REDOX?
Redox stands for oxidation and reduction reactions. An oxidation reaction occurs when a species loses an electron or electrons. Reduction occurs when a species gain an electron or electrons. An easy way to remember this reaction is by the mnemonic device: LEO the lion says GER, which stands for "Lose Electrons Oxidation" and "Gain Electrons Reduction."

What is voltage?
Electrons have the tendency to move from one point in a circuit to another. Voltage is the "push" that causes the electrons to move from a region of more electrons to a region of fewer electrons. The greater the voltage, the greater the pressure that moves the electrons through the circuit. Common household batteries have low voltages, so a shock from one would not harm a person. Even a shock of a couple thousand volts that you get when static electricity shocks you from dragging your feet across a rug has such a low current that it can't harm you at all.

What is a battery?
A battery is a device or series of devices connected together that use a chemical reaction to create and store electrical charge. You can think of a battery as a can full of chemicals that free electrons. Common dry cell batteries use ammonium chloride, zinc chloride, and manganese dioxide enclosed in a zinc cup or cover to produce charge. The battery then holds and releases this charge when the battery is connected into a complete circuit. The speed of electron production by this chemical reaction determines how many electrons can flow between the terminals. Electrons flow from the battery into wire and must travel from the negative to the positive terminal for the chemical reaction to take place. That is why a battery can sit on a shelf for a year and still have plenty of power -- unless electrons are flowing from the negative to the positive terminal, the chemical reaction does not take place. Once you connect a wire, the reaction starts.

What is a potato and how can it make a voltage?
A potato is a South American herb that is a member of the nightshade family. People eat the starchy tuber of the vegetable. So how can a potato create a voltage? Potatoes contain phosphoric acid. It's the acid in the potato that allows a chemical reaction to take place. The potato battery works when a copper penny and a zinc-coated nail are placed in contact with the phosphoric acid inside the potato. The nail and the penny become the battery's terminals or electrodes. The acid reacts with the copper and removes electrons. The copper penny ends up missing some electrons, which gives it a slightly positive charge. The acid also reacts with the zinc nail. In this case the acid dissolves the zinc and leaves some of its electrons behind on the nail. The excess electrons on the nail and the lack of electrons on the penny result in the creation of voltage in the system. If the nail and the copper penny are connected together with a wire, the excess electrons move from the zinc nail to the positive charge on the penny. These moving electrons are called electrical current.