The electrochemical series

A battery can make electrons move through a wire. It is a source of electric current. The voltage of the battery shows how strongly the electrons want to move from one side of the battery, to the other. We can construct a simple battery, using two different metals: One metal where the atoms give away electrons, becoming metal ions. And another metal that starts out in ionic form, and picks up electrons.

Here it’s magnesium atoms that are giving away their electrons… ...and copper ions that are picking up electrons. The electrons are moving through an electrical conductor. The voltage in the conductor is determined by the difference in nobility between the metals. This voltmeter shows how much more noble copper is, than magnesium. To compare the nobility of several different metals, we need to set up the experiments the same way every time.

To do that, we construct the experiments using certain rules – a standard way of measuring nobility. In this case, we are measuring the voltage between metallic magnesium and copper ions. [1] The metallic magnesium should be placed in a solution containing magnesium ions. [2] The solution containing copper ions should be in touch with a piece of metallic copper. [3] And then we make sure that there is the same number of ions in both solutions – the same concentration of magnesium ions and copper ions. When these exact conditions are met, the voltage between magnesium and copper is 2.71 Volts. Copper is 2.71 Volts more noble than magnesium. Using this method, we can compare different metals with each other and place them on a scale of nobility.

Voltage means potential difference, so this scale is called the electropotential series. Magnesium is here; copper is here. The distance between them on the scale is 2.71 volts. If we measure the voltage between copper and silver, we get 0.46 volts. Silver is 0.46 volts more noble than copper.

What will the voltage be between magnesium and silver then? The sum of the two distances: ...3.17 volts. At the very top of the electropotential series, we find gold. This is the most noble of all metals. At the bottom of the scale, is lithium.

The difference between lithium and gold is 4.56 volts. Here is a 4.5 volt battery. So, is it a lithium-gold battery? No. We can connect several batteries as cells, to increase the voltage.

Inside this battery there are three cells, each providing 1.5 volts. And this car battery has six cells with 2 volts each, making a total of twelve volts. So, the voltage between two metals is determined by how noble the metals are relative to each other. We can measure the difference in nobility using a voltmeter, and place the metals on a voltage scale - the electropotential series. The greater the difference between two metals on the scale, the higher the voltage between them.

Batteries often contain several electrochemical cells, so that they can supply an even higher voltage.