Why sugar solution doesn't conduct electricity

Melts and solutions of salts

Ionic compounds have certain properties

Due to the forces of attraction acting on all sides, the ions are bound quite tightly in the ion lattices. They only perform oscillations around the lattice points that they occupy in the ion lattice. As a result, ionic compounds are solid at room temperature. Only by applying a great deal of heat can the kinetic energy of the ions be increased so that the lattice forces are overcome and the ion lattice disintegrates. At this moment the ionic compound has reached the melting temperature, which is relatively high for these substances. The boiling point is still much higher.

saltMelting
Point
Boiling
Point
Sodium chlorideNaCl800 ° C1440 ° C
Potassium bromideKBr728 ° C1376 ° C

Some salts, especially salts of organic acids, decompose when heated before the boiling temperature is reached, some even before the melting temperature is reached.


Electrical conductivity of melts

As the name suggests, one can imagine the electric current as a flow (flowing, currents) of freely moving charge carriers.

If you hold the free ends of a conductivity tester in the solid salt potassium nitrate, you will see that it has no conductivity. If you now carry out a conductivity test in the melt of potassium nitrate (ionic compound), one suddenly observes conductivity, while in the melt of naphthalene (molecular compound) there is no conductivity. Naphthalene is a solid made up of molecules with the composition C.10H8.

In the solid state, the ions are bound to the lattice sites. When the ionic compound melts, the cohesion of the ions is loosened. You leave your grid places and can now move freely in the liquid melt. Since the lattice energy has to be overcome before ions can move freely, salts have a high melting point. Solid naphthalene can be melted very easily because its molecules are not held together very well. The naphthalene molecules move in this melt, but they are not charge carriers.

If a current is transported in a melt, this indicates mobile ions. In contrast to uncharged molecules (such as naphthalene), they have a positive or negative electrical charge.


Electrical conductivity of solutions

A salt solution also conducts the electrical current, because when a salt crystal is dissolved, the ions bound in the lattice are set free. As charge carriers, they can now move freely in the solvent and conduct the electrical current. The situation is different with a sugar solution: Since the sugar molecules in the water are not charge carriers, the solution cannot conduct electricity.

In summary, salts usually have high melting and boiling points and their melts conduct electricity. Chemical compounds that are based on an atomic bond usually have low melting and boiling points and are classed as non-conductors. Ions can be detected in melts and solutions by conducting a conductivity test. In spite of their ionic structure, salts in the solid state are mostly non-conductors. The binding forces between the ions are too great for individual ions to move freely. If salts are melted, this changes. The ions are no longer bound so tightly to their neighboring ions and so molten salts can transport the electrical current through ionic conduction.