In this video, we'll conduct experiments exploring a word you might have heard in the media, or in marketing commercials for sports drinks. Electrolytes, what exactly is an electrolyte? It's time for you to predict whether or not each of several substances tested will be able to complete the circuit. And conduct electricity to light up the bulb upon submersion of the electrodes in the circuit. Here are two incandescent light bulbs that are plugged into our power outlet. But they are not lit, because the circuit is not closed. The two copper electrodes are pointed down, but they are not touching each other. First, Dr. Lyle is using a piece of metal with a grounded rubber handle, to show that the circuit can be completed by connecting the copper electrodes with a piece of conducting material, metal in this case. A 40 watt light bulb is in the apparatus on the left, and a 15 watt light bulb is in the apparatus on the right. Please note how brightly these bulbs glow when the circuit is closed by an excellent conductor. Next you are going to predict how well each substance on the list, will complete the circuit. And then we will do the experiments and make observations, to either support of refute your predictions. Again remember that solutions with three mobile ions, will complete the circuit and light up the bulb. Thus, these types of substances are called electrolytes. The in video quizzes for making your predictions in this demonstration will be in small groups of two to four samples. So before we show you the first experiments please make your predictions about the first set of substances to be tested. Number one will be a 0.1 molar aqueous solution of ammonium chloride. Number two will be pure liquid methanol which is more commonly called wood alcohol. And number three will be solid sodium chloride salt. Go ahead and make your predictions now about whether or not these substances are electrolytes. Thank you for making your predictions. First Dr. Lyle is testing the 0.1 molar solution of aqueous ammonium chloride. As you can see this solution completes the circuit quite well, resulting in a bright glow from the 40 watt lightbulb. This solution is a strong electrolyte. Since it works well for the higher power bulb, we know it will also cause the lower power, 15-watt bulb, to light up quite brightly. So the 0.1 molar solution of aqueous ammonium chloride is a strong electrolyte because it contains many free ions that can flow freely in the water and complete the electric circuit. In between each of these experiments we are unplugging the apparatus and cleaning off the electrodes. We will show you that just this first time,but be reassured that Dr. Lyle is doing this between each sample. Next is the pure liquid methanol. Dr. Lyle has plugged the power supply back into the bulb but observe that the methanol will not cause either bulb to light up. That indicates that there are, not, free ions in the methanol. It is a non-electrolyte liquid. It does not dissociate into ions. Third, Dr. Lyle is testing to see if the solid sodium chloride salt will complete the circuit. We know that sodium chloride is comprised of sodium cations and chloride anions. But aha! The sodium chloride by itself is not an electrolyte. It won't complete the circuit and light up the bulbs. Why do you think that is the case? [NOISE] So far we've learned that electrolytes must contain free mobile ions. What do you know about a solution of sodium chloride in water? Will the solution contain free ions? Of course it will. And you have learned how to write the dissolution chemical reaction equation for the process of sodium chloride salt dissolving in water. So, are aqueous solutions of sodium chloride properly termed electrolytes? Let's start by examining a fairly dilute solution. Here, Dr. Lyle is testing an aqueous sodium chloride solution with a concentration of only 0.001 molar. That's quite dilute. The higher power bulb doesn't light up at all. But the lower power bulb does give a dim glow, indicating that some mobile ions are present in the solution to conduct the electricity. The sodium chloride does completely dissociate in the water. But for this sample, the concentration is so low that the solution still doesn't conduct the electricity very well. Now let's examine a more concentrated solution of sodium chloride and water. This time with a concentration of 0.1 molar. This time the higher power bulb glows very brightly, indicating a strong electrolyte solution. Let's continue by making predictions for the next set of substances to be tested. Concentrated ammonia. Dilute Ammonia and dilute Acetic Acid. In the cases of the dilute solutions they are zero point one molar solutions in water. Thank you for making your next set of predictions regarding the Ammonia and the Acetic Acid. First in the set is the concentrated ammonia, which has the formula NH3. This one is interesting. The higher power 40 watt bulb does not light up at all. So the concentrated ammonia is not a strong electrolyte. The lower power, 15 watt bulb, does light up a little bit, although the glow is quite dim. That is because a little bit of water has gotten into the sample. Just as it was sitting out in the open container in the air. In other words, it's not quite pure and hydrous ammonia. The ammonia, which is a weak base, reacts with water to eliminate extent, and that reaction produces a relatively small number of ammonium and hydroxide irons. If we dilute the ammonia by adding a large amount of water to it,. Then the solution remains a weak electrolyte, and the light bulb gives off a slightly brighter but still rather dim, glow. The next sample in this series is dilute acetic acid, which is a component of household vinegar. Acetic acid is a weak acid, meaning it reacts with water to a small extent to make a few free irons. But most of the acetic acid remains intact upon dissolution. So, the 40-watt bulb remains dark, but the 15-watt bulb gives a dim glow when the circuit is completed with the dilute acetic acid. Solutions that behave this way are termed weak electrolytes. So aqueous solutions of weak acids or weak bases are weak electrolytes. What about strong acids or strong bases in water? Do you predict that an aqueous solution of a strong acid or a strong base will be a strong electrolyte, a weak electrolyte or a non-electrolyte. Let's test your prediction by conducting the experiments. The first one in this set is 0.1 molar sodium hydroxide. Sodium hydroxide is a strong base, and the sodium cations and hydroxide anions completely dissociate in the water. Because it has a large number of mobile ions, the solution is a strong electrolyte. The same is true for the 0.1 molar hydrochloric acid solution in water. Because hydrochloric Acid is a strong acid, and it reacts extensively with the water it produces hydronium cations, and chloride anions. In both of these cases of a strong acid or a strong base, the resulting solution is a strong electrolyte and conducts electricity well. Let's conclude our demonstration by exploring four liquids you can probably purchase at your local grocery store, sugar water, deionized water, a sports drink and some apple juice. Which of these do you think will cause the light bulb to light up. Thank you for making your prediction. First, let's see if the sugar water is an electrolyte, this solution is a non-electrolyte. Although the sugar does dissolve fairly well in the water it does not dissociate into ions as it dissolves and therefore the solution does not conduct electricity and light up the light bulb. The ionized water, as the name suggests, does not contain any ions so it is a non electrolyte. Finally, what about sports drinks, which are often marketed as containing electrolytes versus apple juice. Which likely contains a great deal of sugar. But is the apple juice also an electrolyte? Thank you for joining us today for this demonstration about electrolytes.
