Another question we might ask is what is the nature of sodium chloride, aqueous, or aqueous sugar, or aqueous acetic acid, vinegar? In other words, if we had 0.10 molar solutions of each of these substances, what would we have in the solution itself? We can get a good idea by performing a simple experiment. We will make use of only one definition. An electrolyte is a substance that dissolves to give a solution that contains ions and therefore conducts electricity.
Now for the fun. This simple device is constructed such that the light bulb will glow if the copper electrodes are placed in a solution that conducts electricity when the current is switched on. In order to conduct electricity, the solution must contain ions.
In this demonstration, we are going to test several simple solutions for the presence of ions. The first solution that we are going to test is 0.1 molar sodium chloride, NaCl, or common table salt. Now we'll add the copper electrodes and place them in the solution and throw the switch.
Notice how brightly the light bulb glows. This means that this solution contains a lot of sodium plus and Cl minus ions and therefore it conducts electricity. Next, let's test 0.1 molar hydrochloric acid, HCl. Most of you are familiar with this strong acid, HCl, and I'm sure that you can predict what will happen. Put the electrodes in the solution.
and throw the switch. Notice again the light bulb glowed very brightly and I'm sure you predicted that because HCl is a strong acid. This means again that in this solution we have H plus ions and Cl minus ions and these ions conduct electricity.
Our next solution is also familiar to you. This is 0.1 molar acetic acid or CH3. COOH or common vinegar. Let's put the electrodes in the acetic acid solution and throw the switch. Notice how dimly the light bulb glows.
This means that there are very few ions in the solution and that acetic acid exists in the solution as acetic acid molecules. This is the reason why the light bulb glows. glowed only dimly and certainly not as brightly as in the previous two cases.
Our last solution is a 0.1 molar glucose C6H12O6 which is just common sugar. Okay now let's add the electrodes to the solution and throw the switch. Notice in this case no matter how long we wait the light bulb does not glow at all.
This means that there are no ions in the solution whatsoever and therefore no electricity is conducted. Now to finish off our demonstration, let's test common tap water. Would any of you like to predict what will happen with the tap water when we add the electrodes?
Write down your prediction. Notice the light bulb glows very very faintly. Would you care to give an explanation for why the light bulb glowed very faintly? Well, tap water contains sodium ions, calcium ions, and magnesium ions in very low concentrations, and these conduct electricity, and consequently, the light bulb glows.
In fact, you may remember that calcium 2 plus and magnesium 2 plus are responsible for hard water. When we continue this lecture, We will make a table which summarizes all of our observations from this demonstration. This is a very important demonstration because the demonstration tells us about the solution itself and whether we have ions or molecules in the solution. This is doubly important when we consider chemical reactions because we will know which species are reacting. Let's summarize our results in a table.
We have five experiments here. And we're going to look at the nature of the solute, what happened with the light bulb, and the conclusions. So for 0.1 molar sodium chloride, the light bulb glowed very brightly, and our conclusion was that we have mainly ions in the solution. For 0.1 molar hydrochloric acid, which we all know as a strong acid, the light bulb also glowed very brightly. And the conclusion was the same, that is we had mainly ions in the solution.
However, for 0.1 molar acetic acid, or CH3COOH, the light bulb only glowed very weakly. And our conclusion was that we only had a few ions in the solution. For 0.1 molar sugar, C6H12O6, the light bulb did not glow at all.
So therefore, we concluded there were no ions in the solution. And lastly, I got you to predict what would happen with tap water, and we got a faint glow from the light bulb, and we concluded that there were very few ions in the solution, and these could have been due to the hard water component of tap water. This experiment leads us to some practical classifications of solutes and the nature of their solutions.
or actually what exists in aqueous solutions as opposed to what we put in. Consider the following definitions. Strong electrolytes are substances that exist in solution exclusively as ions and their solutions are strongly conducting.
Examples of strong electrolytes are common table salt sodium chloride, hydrochloric acid, and the common base sodium hydroxide. Weak electrolytes are substances that exist in solution as an equilibrium mixture of ions and molecules, and their solutions are weakly conducting. Examples of weak electrolytes are acetic acid, which we used in our demonstration, hydrofluoric acid, HF, and ordinary household ammonia, NH3.
Non-electrolytes are substances that exist in solution exclusively as molecules, and their solutions are non-conducting. Examples of non-electrolytes are sugar, we used in our experiment, methanol, which is common wood alcohol, and acetone, which is a common solvent.