Hello, and welcome to the discussion about solutions, and solutions that happen to conduct electricity... or not. So what happens when a solute dissolves? Go ahead and listen to the lecture notes about solutions and solutes. But as a review, a solute is a substance that's going to be dissolved. And so this solute could be molecular, or it could be ionic. Some molecular solids that you're familiar with would be sugar, hydrogen peroxide, alcohol... like rubbing alcohol. An ionic solid that you're familiar with would be sodium chloride, or sodium bicarbonate maybe. This is baking soda. And when you put these in water , the intermolecular attractive forces can be overcome. So there are IMFs that keep your solute particles attracted to each other, But there are also IMFs, or intermolecular attractive forces, between the solute and the solvent. And if the solute-solvent interactions are stronger than the solute interactions, then the solute will dissolve. So if these attractions are strong, the solute will dissolve. And once you have a solution, then you might have a solution that conducts electricity. So a solution that conducts electricity is either an electrolyte or a non-electrolyte. So non-electrolytes... let me go back up. Electrolytes are materials that dissolve in water to form a conducting solution. So ionic compounds will dissociate, and they'll either dissociate 100 percent or partially. So if I put sodium chloride in solution, I'll get Na+ ions floating around and chloride (Cl-) ions floating around. If I have a material that dissolves completely as ions, I will use a single reaction arrow to the right. But if I have a solution that dissolves mostly as molecules and a little bit as ions, I will write a double reaction arrow, to indicate that some of the solution is ions, but most of it is molecules. And it'll conduct electricity, but not as well. So non-electrolytes will not dissolve as ions. They will not dissociate. and an example of a non-electrolyte is hydrogen peroxide. So hydrogen peroxide, if I put it in water, remains as hydrogen peroxide. There are no ions formed at all. So I want to show you guys a video of a demonstration that I like to do when I'm teaching face-to-face, but I found a video instead. So go ahead and watch this video. The term electrolyte is a term used when talking about solutions with water as the solvent. We'll demonstrate the property of being an electrolyte with an electrical conductivity tester like this. Pure water does not conduct electricity. I will put the electrodes of the apparatus into the beaker of water. There's no light coming from the light bulb If I dissolve a material in this water and the light lights very brightly, the dissolved material is called a strong electrolyte. As an example, here is a small amount of table salt. I'm going to add just a little bit to the water and stir it up As it dissolves, the ions of sodium and chlorine, which are charged particles, go into the water, which will now allow the solution to conduct electricity. So the ionic substance table salt or sodium chloride is a strong electrolyte. The term non-electrolyte refers to a substance which dissolves in water but does not allow electrical conductivity. Here is some sugar, which I will dissolve in the water. As the sugar dissolves, the light does not light up, so sugar is a non-electrolyte. Some acids and bases are also strong electrolytes. Here's an example of some hydrochloric acid. Only a little bit in the water. Water... and about 10 drops, will allow the light to light up very brightly. So the acid is also a strong electrolyte. Therefore, it's called a strong acid. Acetic acid on the other hand dissolves, but allows very little electricity to go through the water. See how the light bulb gives off much less light with a lot more acid. Thus we call acetic acid a weak electrolyte. And it is a weak acid. So we have strong electrolytes, weak electrolytes, and non-electrolytes. And as you saw in the video, there was a discussion about and a demonstration about acids. Well, acids happen to be molecular, because the electrons are shared between the hydrogen and either the polyatomic ion or the other ion, -um- like iodide or chloride. But the electrons are mostly shared until you put them in water and they ionize. So there are several definitions of acids. And one of the definitions is that acids ionize to form H+ ions. So when I'm talking about acids, I'll try to use the term ionize instead of dissociate. When I'm talking about ionic compounds, I'll use the term dissociation. So one of the interesting things is the early definition is that acids form H+ ions. But really what's happening whenever you have an acid in the presence of water, the H+ and the water come together to form what's called the hydronium ion H3O+. Often these terms are used interchangeably. But know that this is really the species that's in solution. And then bases dissociate because bases are ionic, dissociate to form hydroxide ions. But you can have some bases that are weak bases, like ammonia, that literally because of the lone pair and this strongly negative... dipole on nitrogen, we'll pull off a hydrogen. And I'm going to use a double arrow because this is a weak base. and I can get NH4+ ammonium and hydroxide in solution. So there are strong bases that will dissociate to form hydroxide, and there are weak bases that are typically ammonia-containing or nitrogen-containing bases, that will make hydroxide in solution by interacting with water. So -um- we like to use universal indicators.... (Hold on. My device is not responding. Yikes, it's frozen!) So we like to use a universal indicator to indicate whether a solution is acidic or basic. and acids are going to have a pH below 7, and bases are going to have a pH above 7. So anything that has a hydroxide in solution will have a pH above 7. Anything that has hydronium ion, in solution will have a pH below 7, and neutral is at 7. So acids can be strong. If they are strong, they will ionize 100 percent. And notice I'm using a single reaction arrow here. I have only chloride and hydronium ion in solution. Or acids can be weak. And you have an unequal reaction arrow or you can have at least two arrows, showing that only a fraction of the molecule has dissociated or ionized. And I'm just going to draw the... Lewis structure for acetic acid. So this is acetic acid. And because of resonance stabilization, also known as delocalization, this molecule can partially ionize to form the carboxylate ion. And you can have resonance stabilization along in here. So if I were to draw the resonance hybrid it would be something like this and because of that, the H+ can come off and I can have H+ in solution. If this is in water, which it is, I could also draw H3O+. Either one of those works. So you have a series of strong acids and weak acids. And the acids that you want to memorize that are strong are the nitric, sulfuric, and perchloric acids, and then also hydrochloric, hydrobromic, hydroiodic. All the other ones are weak. You're actually going to see that too, phosphoric acid. So some -um- I mean some textbooks won't rank phosphoric acid as strong. But you'll notice in your lab today that phosphoric acid is... has a quite a bit of conductivity. You'll compare the phosphoric acid to hydrochloric acid and you'll see it's not even close. But there is quite a bit of conductivity in phosphoric acid. Now bases can be strong as well. And if they dissociate, because they're ionic, 100 percent, notice the single reaction arrow, they'll make separate ions that will conduct in solution. And you can have weak bases. I show this one where you have ammonia and water makes ammonium hydroxide. And only a small fraction of the solution contains ammonium and hydroxide. And then there's still the reactant, so you have ammonia in solution as well. The bases that you want to memorize that are strong are going to be the hydroxide containing bases. -um- There are stars next to the alkaline earths, like calcium, strontium, and barium hydroxide and also magnesium hydroxide, because -um- they're not very soluble in water. They're uh.... If you try to dissolve them they just kind of don't dissolve. But any little bit that does dissolve dissolves 100 percent. And then weak bases. You'll find the bicarbonate anion. Ammonia we've talked about. And there's a bunch of weak bases. If it's not strong, it's considered weak. So that can be helpful. And then you have solutions or compounds that can be acidic and basic. -uh- Water is a very important one. So one of the reasons that water is so important for life is that it acts as both an acid and a base inside of our body. So it's constantly -um- helping reactions occur. And if -um- water is going to act as a base, the lone pair on on the oxygen can accept a proton and become the hydronium ion. If water is going to as an acid, then the lone pair will be donated, and you'll end up.... I'm sorry. The hydrogen will be donated. You'll end up with hydroxide. And then you'll have the H+ that's able to go ahead and act like an acid. So water is called amphoteric. So from this -um- definition, I'd like you guys to try to predict which of the following solutions would be an electrolyte or not an electrolyte. Glacial acetic acid is acetic acid that's a liquid and has not dissolved in water. And then acetic acid that's aqueous, HC2H3O2 aqueous. You can go ahead and look back at the notes. In the video you'll see hydrochloric acid. Oh, and you'll see acetic acid. Sucrose is sugar. So go ahead and look at the video if you need to. And then sodium chloride was also tested. And that's it!