Sea Water and Conductivity

The conductivity of sea water is of great importance to oceanographers around the world. It is through knowing how well sea water conducts electricity that they are able to determine the salinity of sea water and consequently the density of it. These two factors help scientists to learn about the bodies of water that cover over seventy percent of Earth's surface and are therefore of great concern to humanity as inhabitants of this planet.

Sea water is obviously water in or from a sea. A sea is defined as a great body of salty water that covers much of the earth. The ocean is Earth's largest sea, taking up the majority of the surface of the planet.

Sea water, or salt water as it is sometimes called, is composed of water (hydrogen and oxygen) plus a substantial quantity of dissolved solids that come from the erosion of rock material on the earth. If all the salt in the ocean were dried out, it would form a solid mass the size of Africa. The most plentiful salt is sodium chloride, or table salt. It is the salt distinguishes sea water from freshwater found in most lakes and rivers, and it is the salt which makes the water in the ocean undrinkable by humans.

Salinity is the measure of the dissolved solids in sea water. On average, ocean water has a salinity of 35 parts salt to 1000 parts sea water. This can vary because of several factors. Sea water of above-average salinity can be found in areas with hot, dry climates and near sea ice in polar regions. Sea water of below-average salinity can be found near places of heavy rainfall and where freshwater enters the ocean. Salinity can be helpful in identifying different water masses within the ocean.

Conductivity is the ability of material to let a flow of electric charge or a current pass through it. In solid materials, a current is carried through the movement of electrons. In a gas or a solution, it is carried by ions. Materials that let a current flow easily are known as conductors, while those that do not are known as insulators. Most metals are good conductors, and plastic and glass are good insulators.

The solids dissolved in sea water allow it to conduct electricity. The higher the salinity of sea water is, the better a conductor it makes. This fact can be used to determine salinity through the testing of how well sea water can conduct electricity. This method of determining salinity is far quicker and more accurate than finding it through evaporation.

In the demonstration, several samples of water, one distilled, one from the tap, one with a high concentration of salt, and one with a low concentration of salt, will be used to attempt to complete the electrical circuit between two pieces of metal. One is connected to the power source of the device, the other is connected to the light bulb.

Since increased salinity means greater conductivity, the sample with the highest salt content ought to cause the bulb to burn the brightest. On the other hand, the distilled water should not cause the bulb to light up at all, since distilled water contains no salts. Tap water contains some minerals, so it should cause the bulb to glow dimly.

Now to summarize what has been said: Sea water is water containing dissolved solids. It covers over seventy percent of the surface of the planet. It is a good conductor of electricity, because it allows a current to pass through itself easily. Testing how well sea water conducts electricity is a way to determine salinity, which has several applications in the field of oceanography. Studying the ocean leads to a greater understanding and appreciation of the ultimate wonder of the world.

Copyright © 2002 Colleen Fischer | Last updated October 7, 2002