Why does salt and distilled water conduct electricity?

Answer 1

Conduction in a liquid or solid requires charged particles that are free to move to carry the electrical charge from one place to another (this is what is meant by the 'current'). In metals, metallic elements have just 1, 2 or 3 electrons in the outer orbits of their atoms, that are loosely bound to the atoms and therefore can flow through the solid metal crystal lattice. It is these electrons that form the current. In water, however, the water is made from molecules that are not charged and hence pure water does not conduct particularly well. Adding the ionic solid salt (comprised of positively charged sodium ions and negatively charged chlorine ions) enables these ions to mix into the water by dissolving, and enables them to be free to move around. As these are charged, they carry the current through the solution and so salt water is a conductor.

Answer 2

Short Answer:

Salt water is a pretty good conductor of electricity. Its not as good as a metal, but still, it is far from being an insulator. Pure water does not conduct electricity well at all. Salt water has sodium and chlorine ions in it and because the are charged, they move when you apply a voltage and the moving ions are the actual current.

Long Answer:

The electrical conductivity of water, both pure water and water with dissolved salts, does not work like conductivity in a metal. (In a metal, the outer electrons of the metal atoms are not tightly bound to specific atoms but rather distributed widely and are pretty much free to move in response to an electric field. When you apply a voltage to a metal you get a large flow of electrons.)

In water, the application of a voltage results in the movement of charges, but the charges are not nearly-free electrons but rather ions (charged atoms or molecules). In pure water, the ions that are moving are the protons in the form of H3O+ and hydroxide ions, OH-. In other ionic solutions it is the dissolved ions themselves, for instance in salt water, sodium chloride dissociated into the ions Na+ and Cl-.

When a voltage is applied in water, there develops an electric field, E, as expected. Any atom or molecule that has a net charge, q, feels a force, F=qE. Positive ions move in the direction of the field and negative ions move in the opposite direction. Both sets of moving charges add to make a current flows that in the direction of the field.

Of course, one expects that dragging an atom or molecule through a liquid is a lot harder than moving an election through a metal and thus one is not surprised that the conductivity due to ion motion is small. Sea water conducts electric current about a million times better than pure water and drinking water varies, depending on the source, but might be a hundred to a thousand times more conductive than pure water. A metal, like gold, copper, aluminum will be a million times better than seawater at conducting electricity while an insulator like glass or rubber is a million times worse than pure water.