This is the first video / chapter, 11 and 13 / intermolecular forces I'm going to take a look the first question that we actually began with in class I'll, take a look all the way down here on page or let's. Take a quick look at this question right here. So the question asks us we give the have three compounds I'll just review the molecular forces on these three compounds asked ill and won't open all and butane, oops, and they're, giving us the structures of the molecules themselves. Remember.
There are three in America forces, we have lemon dispersion. We have dipole-dipole and we have hydrogen bond. And the idea here is the London dispersion operates in nonpolar molecules.
This here butane is a non-polar molecule and dispersion forces. Then the bigger the molecule, the stronger, the dispersion forces. So this actually molecules aren't, very big. Butane. Turns out to be a gas as you may know, even though it's using butane lighters and the pressure to remain a little all right 1-propanol.
Versus answer to an acetone is polar. So because it's polar, and it's polar because it's a symmetric, because you have an oxygen on top. This would be a polar molecule and 1-propanol has hydrogen bonding. So polar molecules will have dipole-dipole forces. Hydrogen bonding will be present in three possibilities. You can have a fluorine, or you can also have a nitrogen flowing.
Turns out to be strongest because the most electronegative then oxygen and then nitrogen is the third most electronegative. Element on the back table. The reason again, why hydrogen bonding exists in these three cases is because these elements extra high electronegativity pulls the electron off of the hydrogen, exposing the positive charge, getting a very, very positive charge in these cases. Now it should be said that 1-propanol will actually have all three of these forces, operational London, dispersion applies to every molecule. If you have electrons, you've got London dispersion because 1-propanol is also polar because. It's asymmetric, because you have an oxygen on the right side also has dipole-dipole.
So butane only has London dispersion. A stone has London, dispersion and dipole and propane has all the forces available. Now these four is an influence of physical properties, not chemical, but physical properties. So the question asks us, which is a list of the compounds in order of increasing volume points.
We should say that the highest boiling point will be propane, because it has the highest or the. Strongest intermolecular forces, the lowest boiling point would be butane. It has the least analytical forces.
Now notice they give us the same molar mass and that's because dispersion forces will be as we'll see in a minute dependent on the size, which is the mass of the molecule. So let's come back up to page one. And let me actually take a look at some of these questions here.
So if you take a look I, guess a quick look at number one, it asks us or number two rather asks us based on the data in the. Table on the left, which of the following liquid substances has the weakest intermolecular forces. So the table gives us vapor pressure. Now, babies pressure, essentially is how quickly a substance evaporates.
Notice the substance with the highest vapor pressure is this guy here chop the highest vapor pressure means that above the liquid phase the molecules, evaporate very quickly. And if you were to close the container, it would give you the highest pressure it's, a gaseous version of the liquid oil. Gives the highest pressure, which means the liquid has the weakest forces.
Now this is, this may be signing confusing because we have 0 H here. So it looks like we have hydrogen bonding. So it looks like it shouldn't be the answer hydrogen bonding gives you strong. Intermolecular forces do not yes.
It does. However, chop is a tiny molecule, it's a very, very small molecule. It is a liquid, but it's an it's, a low boiling of liquid.
You can say easy to vaporize. So you would still pick chop, even though it has. Hydrogen bonding because of the physical property and here they're not telling us. But here you can see that the sizes of the molecules have actually a big effect, right? So if you take a look at a similar question, right down below number five. So number five, for example, says, consider the molecules representing above and in the table below.
So here we have no name here. We have two three, four, try floral pentane. Notice, their boiling points are significantly different. Online has a higher boiling.
Point now you notice right away that nah mean is nonpolar, which means the only force operational all London dispersion. This guy here, two three, four try flora pentane is polar. So you have dipole-dipole forces. Incidentally, you do not have hydrogen. Bonding can be careful.
You don't have hydrogen bonding because flowing is not attached directly to a hydrogen. It has to be on hydrogen to exhibit hydrogen bonding. So the flooring can pull hydrogen's electrons away, exposing its nucleus. So no hydrogen. Bonding here you have dipole-dipole, you also have London dispersion forces, but turns out non-native winds in the overall forces because it's so much longer it being longer actually overpowers this guy being pulled. So the question is going to ask here, they are, they have almost identical molar masses. Now notice they have identical moral math, molar masses because fluorine is heavier essentially than carbon that makes up some molar masses, but nonage has really high boiling point.
And this is. Because nah mean is longer, and so dispersion forces are greater the longer the molecule, the more dispersed, the electrons can be. So you can disperse more on the left side, less on the right side, creating more of a negative more of a positive, partial charge and that's the idea. So C would be the U.S. answer. If you read through the possible answers, the carbon chains are longer running, then they are in the plural pentane compound. Right?
So take a look at something on the second page. We may skip this one. But you may recall the heating curve number 7, says, liquid naphthalene at 95 degree Celsius is cool to 30s or beginning at 95. This is a liquid. So right here, what you're seeing and see you're seeing the liquid to solid interchange?
Remember, a standard heating curve that shows all five parts will look like this. A standard that this is a cooling curve, I'm, sorry, standing heating curve that has all five parts will look like this. So here they're signaling out just this portion of this. Cooling curve I noticed, you actually have a super cooling event right here happening at be. But if you want to get the melting point, you can actually determine the melting point of the substance looks like the melting point is about 84. You can see here's the melting point of naphthalene. So go ahead and take a look at the question and try to answer the question as it comes down.
Let's, take a look at page, three and page three asks us. A few interesting questions in trouble. Then all right I.
Take a. Look at number 13, go through okay, 13 asks us. Gas has generated in a chemical reaction sometimes collected by the displacement of water as shown above all right it's. Not sure about well.
We've talked about this placement of water before which of the following gases can quantitatively be collected by this method. So it turns out what we want is you want to match up Walker's water. We know is hydrogen bonding, which means it has all three forces.
So whichever gas. We try to collect that matches waters. Intermolecular forces' water will dissolve. You won't be able to collect it, or you'll lose a bunch of it. So as you're collecting the gas, essentially the water that's collecting the gas will actually keep a bunch of the gas. So working for non-polar substance, nh3 definitely can't be collected because its hydrogen bonding as well. This will dissolve right into Walker.
You can create a very concentrated solution of nh3 in water. And so too. If you take a look so2 is actually Poland if you were.
To draw its Lewis structure, you would have to do that here or memorize its structure. It is Pollard. So if it's Pollard always it also dissolved HCL, you can see right away is polar it'll dissolve co2 is nonpolar. H is nonpolar.
Now co2 looks like this. Now, if you had to guess which one would be less polar or less, Baltimore nonpolar, you would probably go for a ch2. H is a smaller molecule, tiny molecule, not much of it dissolves in water. At all turns out that a little co2 can't dissolve in the. Water, even though it's nonpolar, if dispersion forces actually allow it to slightly disperse to one side and create slightly positive negative poles and dissolve in water.
It has a low solubility, but a much higher solubility then h2 or oxygen, even or nitrogen, even due to the fact that it's a bigger molecule. So nonpolar molecules could be soluble in water. And their degree of solubility depends on their size. Take a look at number 14.
Let's, take a look at 14-14 says, which of the following substances. Has the greatest solubility and this compound here. Now anytime you see on the AP exam or anywhere else, a molecule that looks like this.
We just saw q, c 5, h, 12 considered to be nonpolar. In fact, you have five carbons, technically in a line, surrounded by all possible hydrogen's. This is an organic molecule. Both of you that took organic chem have the advantage here. So because you have yourself a hydrogen on every carbon. So you double them, one, two, three, four, if you get 10 and 11 to 12 that's, how you get. So non-polar that's, the whole point watch for these.
These are all nonpolar, so which will be dissolved nh3. You saw up here has hydrogen bonding out water. Hydrogen bonding out so employer. It is actually a salt now salt. It should be said, salts are usually very soluble in water. Why are they soluble in water? Because water is very polar hydrogen bonding and salt is permanently having a positive and a negative assault has a positive permanent positive or negative.
Charge water comes the closest to being so. Positive and so negative due to the fact, but it has very strong hydrogen bonding forces. Now these are not full positives. Typically we do a little delta, which means partial positive, partial negative, our molecules have partial positives.
Partial negatives salts have full partial full-salt wax to be very soluble in water, that's a good thing to remember. So in this case, it's out sio2 kind of looks like its salt type as well. It turns out to be as we'll see in a minute, not salt, but it's also looking I on. It so it's out, in fact, ccl4 is nonpolar. You got a carbon. You have four fluorine all right.
So then this will actually be going its nonpolar. The one that will be soluble. Let me take a look let's. Take a look at a question on page on the last page.
This may be a few comments about some equations. Take a look at this page right here we have number 20 is actually a strange lab type question. See if you can think through it, and I was going to just quickly take a look at 22 and 23 now it's rare that. They'll ask about these type of calculations, but this is kind of a review of two things. Number 22 is a review of percent by mass. And 23 is a review of mole fraction.
We actually take them took a look at more fraction, or which was x percent by mass. So if a compound is fifty percent by mass h2o or a CHO, so for will it Joseph for sulfuric, you can say that there are 50 grams of h2so4 in a hundred grams total, which means if you were to account do some calculations, you have a solution, that's, 50. Grams water and 50 grams h2 so forth.
Now they tell you any time to tell you the density, here's, the density of the solution, then you can actually convert from grams of water into milliliters, because they give you grams per milliliter. You can find out milliliters. And then if you want to know the molarity, you can take that to the leaders will I remember is moles over liters and the moles to get moles. You have to convert grams into moles so that's, how you convert from save % mass kind of take apart.
What the percent mass idea means and then try to get it to moles, try to get it to leaders and do moles over liters this one, the calculations' term about to be very tricky and I, don't know, this was from a natural AP exam or just pulled away the calculations look a bit. Tricky, go ahead and use a calculator for this just. So you can practice 23 says, we have methanol in water by mixing together, some methanol and some water. So we want the mole fraction.
Mole fraction is moles. In this case of methanol, Ch3Oh over total moles, this should be easy enough. This one, you can probably do with how to calculate or try it. You have to convert this into moles by dividing by molar mass of methanol, actually then give you a molar mass of methanol. This may be a, but the numbers are clean. So it sounds like possibly you can do this valve calculator? Try it yeah, get the molar mass of methanol divide, a molar mass of Walker's, 18, divided and try to solve this problem and find what the answer is.
Alright, so we will like. You want we can do this one of these in class, until then.
Dated : 17-Mar-2022