Alright, diving into chapter 11, we're going to start talking about solutions, and specifically starting with solution terminology, as well as defining electrolytes and what they are. So there's the learning outcomes and expectations. Feel free to pause.
So your book starts chapter 11 with the dissolution process, which we're going to essentially use as a mechanism to deliver definitions that we can start discussing solutions, what they are and how they form and things like that. And so mixture is the broadest definition. of putting multiple things together.
And so we're not putting them together chemically, as in we're not changing the composition of the chemicals. We're going to have them still be separate substances, but we're going to put them together at least in proximity. And so heterogeneous mixtures are ones where it's not evenly distributed. As in, you can see distinguishing lines between the different components that make up the system.
And so you could have some kind of trail mix that is a mixture of things. You could also put sand and water together, right? There's very distinct boundaries between the sand here and the liquid here. They're not in the same phase.
They're clearly distinguishable from each other. In contrast, we have homogeneous mixtures. And this is where the components are evenly distributed. That is in, it gives a... uniform appearance.
And so by all intents and purposes, you can't see that they're mixed together. And so this is an example of saltwater. And visually, it's very hard to distinguish saltwater from seawater.
Maybe there's a little refractive index change. But for the most part, it looks like a single thing because the multiple components are mixed together uniformly. And so these homogeneous mixtures are known in chemistry as a solution. And I'll get to this again, but a solution doesn't mean it's liquid.
It just means you have two components that are homogeneous. homogeneously mixed together. And so that's the formal definition of solution. And it takes two things to make a solution.
Effectively, you need a solvent and a solute. A solvent is the dissolving medium, basically the thing with a larger quantity. And a solute is the thing that it dissolves in.
And so this definition gets blurry with 50-50 mixtures. But generally, you have a solvent where there's a lot of something. And then you have a solute where there's a small amount going into that solvent. And when you put those together and make a homogeneous mixture, you have made a solution and so here's just a visual example you can take some iced tea mix which would be the solute when you put that in water and it starts dissolving then you have a solution so you have water on one side the solvent iced tea mix on the other side which is the solute you put them together you get the solution of iced tea and so dissolution is effectively the process with which this solution forms right you start out with water you put the iced tea mix in there together and the process of it dissolving is known as dissolution. And essentially in liquid, well, even in the solid state, it ends up being the solute being surrounded by the solvent molecules.
And so here's just an example showing a sodium chloride, sodium chloride crystals dissolving in water. You can see it starts out as sodium chloride solid, then eventually that starts to dissolve. You see these ion-dipole interactions where the sodium ions and the chlorine ions ions get surrounded by the solute molecules, which in this case is water, and eventually the solid completely disappears and you have a homogeneous mixture or a solution of sodium chloride in water. And so other relevant terminology in terms of describing how much can dissolve in solution, we have something that's soluble, which has the ability to dissolve in a given substance.
Salt is soluble in water. We have insoluble, which is the inability of a given substance to dissolve in a solution. And so in this case, sand in water.
water, it should say sand right there. This is sand is insoluble in water. It won't dissolve. However, salt is soluble. We have similar terminology when discussing liquid-liquid mixtures.
And so a miscible solution is one where two liquids can completely dissolve in each other. An example is ethanol and water. And you can essentially have any ratio of ethanol water, and they will always mix together.
And that's because those two are miscible. You can have liquids that aren't miscible. For example, if you put oil on top of water, this could...
could be gasoline or it could be cooking oil or whatever it is, you'll see two separate components. And so these are immiscible. This is a heterogeneous mixture because you can clearly define the two different components.
There's the oil, there's the water. And so this is known as immiscible. So the liquids can't dissolve in each other. And so one important thing to note about solutions, and we have common nomenclature that we casually use when people say solutions, they typically talk about liquids, but solutions in the sciences means something very particular. It's a homogeneous mixture of two substances.
Now nothing in this definition limits that limits it to just liquids. So you can have a gas gas solution, which is what we're breathing right now. It's nitrogen, oxygen plus a bunch of other stuff. You can have liquid liquid solutions.
That's a main very common ethanol and water. But you can also have some solid-solid solutions like brass and things like that when you mix two components together and it looks like a homogeneous mixture and so it's it's it's entirely possible to have all these combinations mix and match solid with liquid liquid with gas gas with solid so on and so forth all that formally defines them as a solution is there's a homogeneous genius mixture of two or more substances and so again the definitions of solute and solvent still hold true Right. And so if you're putting H2 gas in palladium solid, palladium is the solvent. H2 gas is the solute.
And so it really comes down to what the ratio of those components are. But again, the take home message for this slide is it doesn't have to be liquid. You can have solutions that are solid, that are gas, that are liquid, so on and so forth.
And so the question is, why do these solutions form? Right. Why are some things soluble and not soluble? Why are some things miscible and not miscible? And so again, we're going to try to view this from a molecular standpoint, right?
So we have a solute and we have a solvent as two separate things. And so there's a certain amount of energy that's required to break apart solvent interactions. So you can envision breaking that apart into individual molecules or atoms.
Similarly, you can take a solute and break that apart into individual components. And each of these is going to take energy. But eventually, when you put those together, you're going to have new intermolecular forces, right?
We're breaking intermolecular forces, breaking intermolecular forces. making new intermolecular forces. And the thing that dictates whether a solution is going to happen is, is it favorable for these red and blue spheres to interact, right?
Is the intermolecular forces that you gain out of this mixture stronger or better, or at least as favorable as if you're going to have solvent interacting with itself and solute interacting with itself? And so really it's, it comes down to energetics, right? What's the energetic cost of breaking apart of these interactions and then making these interactions here?
And so we don't actually break everything apart. apart when we put mixtures together, but essentially the thermodynamics is the same. Whether you did it through these steps or you did it directly, it doesn't matter. The question is, what are the intermolecular forces here? How much energy is released versus how much energy does it cost to break these apart?
And so the general solubility rules in terms of predicting if something's going to dissolve, believe it or not, is as simple as like dissolves like. And so things with similar properties like to dissolve similarly. And so nonpolar molecules like to be in. interacting with non-polar molecules.
Ions and polar molecules like to interact because these are electrostatic. They like to interact with each other. And then things that do hydrogen bonding like to hydrogen bond with themselves.
So ethanol likes to be in water. Non-polar things like to dissolve in non-polar things. Polar things and ions like to interact with each other. And so that's one of the reasons that gasoline and water or oil and water don't mix, right?
It's an old cliche statement, but it's all dictated by the intermolecular force. forces. So water molecules are polar.
The oil layer is non-polar. And so it's worth noting that you can put non-polar things in polar solution, right? You can have a dipole-induced dipole interaction, but it's a very weak and unfavorable interaction.
These oil molecules would rather interact with themselves than the water molecules, and the water molecules would rather interact with themselves than the oil molecules. And so that's why you get this phase separation. That's why it's immiscible or insoluble.
They don't like to mix because they're not... not polar likes polar, non-polar likes non-polar, and they don't want to mix with each other. But if you take something like sugar, like glucose molecules, and so that black outline here is a glucose molecule.
It is a polar molecule. It has hydrogen bonding. Water is polar, has hydrogen bonding. Sugar dissolves in water for this reason, right?
And so it wants to interact with similar things. And so you can see all these hydrogen bonding interactions. You can put a lot of sugar in water because this interaction is favorable. Like dissolves light. like non-polar polar don't like to mix.
But if you have polar polar, it likes to mix. If they have hydrogen bonding, they like to mix even more. All right. So that was our definition soup. Go back and review those.
We have terminologies like soluble, insoluble, miscible, immiscible, solute, solvent, solution, mixture, homogeneous, heterogeneous. And this language is worthwhile just because it makes it quicker to discuss these properties. And so when we're defining solutions, we can readily say what the solute and solvent is. and everyone knows what we're talking about. So the other thing we're going to talk about in this presentation is electrolytes.
And so we know solutions are a homogeneous mixture of two different substances. We have a solute and a solvent. Solvent is the more amount. Solute is the less amount.
And of the solute things, we have two different subcategories. We have non-electrolytes and electrolytes. And so non-electrolytes are things that do not yield ions when dissolved. And so it's basically they don't break apart into individual charge components. Instead, they stay as a single component.
And so one of the examples we actually just saw is glucose molecules. So glucose has the formula C6H12O6. You have a solid sugar cube. You throw that in water.
The cube breaks apart, but the molecules stay intact. Right. And so it still stays C6H12O6. It's not like these atoms are breaking apart.
They're just soluble in the water. And so individual molecules are separated. but they're not breaking apart the bonds within that molecule. And so again, going back to our other picture of this, there's a glucose molecule.
If you have a sugar cube, it's a whole lot of these molecules together in the solid. You throw them in water, it breaks apart the solid and makes this hydrogen bonding network, but this molecule is still intact. You'll notice it's still C6H12O6. It just has water molecules surrounding it, making it soluble. And so ethanol is another example of this.
If you put ethanol in water, this is where vodka comes from in alcoholic drinks. It's still ethanol, right? It's still C2H5OH.
It's just surrounded by water molecules that is the solvent that dissolves the solute. So these are non-electrolytes, right? They don't break apart. They stay the same as they were when they first started. Electrolytes do break apart.
And so the classic example of this is sodium chloride, right? So in a crystalline lattice, you have sodium chloride, it's one sodium to chloride, it's charged balanced, this is a neutral species. But when you throw it in water, it's more favorable to be Na plus and Cl minus.
And so that ends up happening during this dissolution process. It's soluble because Na plus interacts through an ion-dipole interaction. to the partial negative charge of water molecules around it. Similarly, chlorine is surrounded by the partial positive charge.
And so it's an electrolyte because it breaks up from its neutral form into charged species. And so basically any salt that's soluble will do this, and so magnesium chloride can fall apart into Mg plus and 2Cl minus. And so effectively in this case one thing turns into two ions, in this case one thing turns into three ions.
And so rather than making one thing in solution, you end up making multiple things. And this will become important when we start talking about colligative properties. And so not all things completely break apart.
Like sodium chloride is an example of a strong electrode. But you also have weak electrolytes and on the spectrum of strong to weak Strong electrolytes completely fall apart right there were neutral to begin with and then you have the positive and negative they separate completely in solution You only have ions floating around So weak electrolytes, on the other hand, they're things that can dissociate into ions, but don't necessarily completely dissociate. And so you can see right here, we have a positive charge, negative charge.
These other guys are neutral. And so some of them dissociated into their ions, other ones didn't. And it's going to depend on equilibrium conditions and solubility and things like that. But for the sake of discussion right now, strong electrolytes completely separate, weak electrolytes partially separate, and then there's a middle ground somewhere in between.
between those. And what's interesting about this is you can actually measure electrolytes with conductivity. And so this is just a fun factoid, like pure water does not conduct electricity. It's the ions in water that allow you to conduct electricity.
And so you can use conductivity of a solution as a direct measure of the electrolyte concentration. So if you have something like ethanol, pure ethanol will not conduct electricity, at least won't conduct it particularly well. But then you take something like sodium chloride potassium chloride that completely dissociates, all of a sudden you have ions floating around in solution.
The water becomes much more conductive. You can actually measure the conductivity via how much light is generated. And so you have strong electrolytes on one end, non-electrolytes on the other, and then everything in between, right?
Some things that partially make electrolytes, some things that don't. The point is, is that just because you start out with one thing and non-electrolyte stays that thing, electrolyte breaks up into its individual components. And so here's just some examples.
You can see a list of strong electrolytes, non-electrolytes, as well as weak electrolytes. What's interesting is we're going to cover this content again, but we're not going to necessarily call them electrolytes. But things that are strong acids, those are electrolytes because they break up into an H plus and then a counter ion.
Also salts, if something has a large Ksp, which is a solubility equilibrium constant, it's really good at breaking up into its individual components. And then. sodium hydroxide, potassium hydroxide, those are bases. And then on the other, the middle ground, these weak electrolytes like weak acids and small Ksp salts. And so they're things that partially dissolve and separate.
And so yeah, a really quick talk on just like the terminology associated with mixtures and solutions, right? A mixture is two things together. Is it homogeneous or heterogeneous? Is it partitioned or not? You can...
Of the mixtures, a solution that's homogeneous or a mixture that's homogeneous is a solution. You have a solute and a solvent. You have the dissolution process of dissolving. You have strong electrolytes, weak electrolytes, and all this is dictated by the intermolecular forces.
You can predict what things will like to go together based on the adage, just like dissolves like. Polar likes to be with polar. Ions like to be with polar. non-polar things like to be with non-polar things. And so you can make pretty good predictions on which solution is going to be more or less soluble based on the intermolecular forces.
All right, so that covers 11.1 and 11.2. We have the dissolution process and the terminology associated with solutions. And then we talked about electrolytes, strong electrolytes versus non-electrolytes and everything in between. Next we'll start getting into solubility in 11.3.