ELECTROLYTES AND NON ELECTROLYTES

Hi Students,

Some of you in this semester learn about electrolytes and non electrolytes. You will develop your knowledge, ability, and skill about solution that you have learnt in the first semester.

Solution is a homogeneous mixture. When a solute is dissolved in water, the result is an aqueous solution. Now please think about this solution.

In aqueous solution, water is a solvent. Remember the properties of water that are important in this discussion. The molecular formula of water is H2O. This molecule consists of two hydrogen atoms and an oxygen atom. There are two single covalent bonds, e.i. O - H. This bonding is grouped as a polar covalent bond, because the electronegativity of both atoms are different. The bonding pair of electrons (BP) is closed to O atoms rather than H atom, because the electronegativity of oxygen atom is greater than hydrogen atom. Remember the Lewis' Electronic Structure. Around oxygen atom, there are two BP and two LP (lone pair). The repulsion of LP-LP is stronger than LP-BP, and the repulsion of LP-BP is stronger than BP-BP. So that there is a negative pole around oxygen atom and a positive pole around both hydrogen atoms. The water molecule is a polar molecule, so as a solvent, we call it a polar solvent.

Now please discuss about an electrolyte. An electrolyte is a substance that dissolves in water to give an electrically conducting solution. When you test water, so it dosn't conduct electricity. Sodium chloride, table salt, is an example of an electrolyte. When most ionic substances dissolve in water, ions that were in fixed sites in the crystalline solid go into the surrounding aqueous solution, where they are free to move about. The resulting solution is conducting because the moving ions form an electric current. Thus, in general, ionic solids that dissolve in water are electrolytes. Crystalline itself cannot conduct electricity, because its ions aren't free to move. When crystalline is melted, so the ions are free to move, it conducts electricity.

Not all electrolytes are ionic substances. Certain molecular substances dissolve in water to form ions. The resulting solution is electrically conducting and so we say that the molecular substance is an electrolyte. An example is hydrogen chloride gas, HCl(g), which is a molecular substance. Hydrogen chloride gas dissolves in water, giving HCl(aq), which in turn produces hydrogen ions, H+, and chloride ions, Cl -, in aqueous solution. The solution of H+ and Cl – ions is called hydrochloric acid and the formula is usually written as HCl(aq). So you have to be careful that the name of HCl(g) is different with HCl(aq).

HCl(aq) --> H+(aq) + Cl-(aq)

A nonelectrolyte is a substance that dissolves in water to give a nonconducting or very poorly conducting solution. A common example is sucrose, C12H22O11, which is ordinary table sugar. Another example is methanol, CH3OH, a compound used in car window washer solution. Both of these are molecular substances. The solution process occurs because molecules of the substance mix with molecules of water. Both substances do not ionize. Water cannot break the covalent bond of both substances. So Because molecules are electrically neutral and cannot carry an electric current, so the solution is electrically nonconducting.

OBSERVING THE ELECTRICAL CONDUCTIVITY OF A SOLUTION
A simple apparatus that allows you to observe the ability of a solution to conduct an electrical current has two electrodes, they are flat metal plates, dipping into the solution in a beaker. One electrode connects directly to a battery through a wire. The other electrode connects by a wire to a light bulb that connects with another wire to the other side of the battery. For an electrical current to flow from the battery, there must be a complete circuit, which allows the current to flow from the positive pole of the battery through the circuit to the negative pole of the battery. To have a complete circuit, the solution in the beaker must conduct electricity, as the wires do. If the solution is noncunducting, the circuit is incomplete and the bulb does not light.

A beaker which contains pure water, the bulb is not light. We conclude that pure water is a nonconductor (or very poor conductor) of electricity. A beaker which contains a solution of sodium chloride in water, the bulb lights brightly. The solution is a very good conductor of electricity, due to the movement of ions in the solution.

How brightly the bulb lights tells you whether the solution is a very good conductor. This solution contains a strong electrolyte or only a good conductor which contains a weak electrolyte. The solution of sodium chloride lights brightly, so we conclude that sodium chloride is a strong electrolyte.

Let us look at such strong and weak electrolytes. hydrochloric acid, HCl(aq); sulfuric acid, H2SO4(aq), calcium hydroxide, Ca(OH)2(aq); sodium hydroxide, NaOH(aq); copper(II) sulphate, CuSO4(aq) are strong electrolytes. Examples of weak electrolytes are vinegar, CH3COOH(aq) and ammonia, NH3(aq).

The other examples of nonelectrolytes are urea, CO(NH2)2; glucose, C6H12O6(aq); and ethanol, C2H5OH(aq).