Skip to main content
Pearson+ LogoPearson+ Logo
Start typing, then use the up and down arrows to select an option from the list.

General Chemistry

Learn the toughest concepts covered in Chemistry with step-by-step video tutorials and practice problems by world-class tutors

14. Solutions

The Colligative Properties

The Colligative Properties explain what happens to a pure solvent as it transitions to a solution.

The 4 Colligative Properties
1
concept

The Colligative Properties Concept 1

clock
2m
Play a video:
Was this helpful?
Now the four collective properties discuss what happens to a pure solvent as a salute is added to it. So they're discussing what happens as our pure solvent transitions into a solution. Because remember when we add salute to a solvent, it becomes a solution, we're going to say as salute is added to a solvent. Some cognitive properties will increase while others will decrease. Now here, when we take a look at boiling point and osmotic pressure, we're gonna say that these two collective properties will increase the more salt we add to our solvent. Conversely, we're gonna say that are freezing point of vapor pressure. The more sought to add to my solvent. The lower they go, okay, so just remember these are the two effects of adding salute to a pure solvent. Now, let's discuss these four collective properties a little bit more closely. So boiling point. Remember boiling point is just the temperature where we're going to have an equilibrium between our liquid and gas phases. Alright, so remember we have our liquid becoming a gas or vaporization and then we have our gas condensing down back into our liquid boiling point. Is when there's an equilibrium between these two changes, freezing point freezing point is where there is an equilibrium between our solid phase and our liquid phase. So, going from solid to liquid, we have melting or fusion occurring and then going from liquid to solid. We have freezing occurring freezing point is when both of these phase change properties or processes are happening at the same time. So they're at equilibrium with one another. Now vapor pressure, we're gonna say here, that vapor pressure is basically the pressure exerted by a gas at the surface of a liquid. We're gonna say this is measurable also, again, the whole idea of being an equilibrium. Finally, we have osmotic pressure. Osmotic pressure is just the force that drives osmosis. Remember the movement of water from an area of low concentration to an area of high concentration. So here we have an illustration where this side is more concentrated and so water would rush towards this side here. What is this? What effect does this have? Well, the right side, the water level be lower and the left side the water has increased because again, water moved from an area of low concentration to an area of high concentration. Right? So we'll go a little bit more in detail in terms of the mathematical applications of each of these collective properties, but for now, realize that they have to do with our transition from a pure solvent to a solution through the addition of some type of salyut

Some Colligative Properties will increase and others will decrease with the addition of solute to a pure solvent.

2
example

The Colligative Properties Example 1

clock
50s
Play a video:
Was this helpful?
Here. Benzene, which has a formula of C6 H six, has a boiling point of 80.1°C. What is a possible new boiling point once an unknown amount of glucose is added to the benzene solvent? Remember, we discussed this earlier on. We say the more salute you add to a pure solvent, then the higher the boiling point would be. So we're going to say here we expect the boiling point to be a value that is now higher than 80.1°C. And if we look at all our choices, the only one that's above this original temperature of 80.1°C is options. See, we expect our temperature, which is reasonable to be 89.6 degrees. None of the other ones make any sense. Boiling point would not stay the same, and it definitely would not decrease. Adding salute to a pure solvent increases your boiling point
3
concept

The Colligative Properties Concept 2

clock
2m
Play a video:
Was this helpful?
now the Van Hoff Factor, which uses the variable I equals the number of ions produced from dissolving a soluble soluble. Now, when we talk about salutes, we group them as being either Ionic or Covalin in nature. Now, remember, ionic compounds are composed of a positive ion connected to a negative ion. That positive ion can be in the form of the ammonium ion or a metal. Yeah, and then that negative ion will be in the form of non metal. So here, if we take a look, we have sodium hydroxide, ammonium carbonate and aluminum sulfate as our three ionic compounds, each one because they're ionic can break up into ions. Here we have an A plus O. H. Minus. Here it breaks up into two ions. We just said that the Van Hoff factor is a number of ions produced when a soluble solid dissolves. So since there's two ions, I equals two. Ammonium carbonate breaks up into two ammonium ions, plus one carbonate ion for a total of three ions. So here I equals three aluminum sulfate breaks up into two aluminum ions and three sulfate ions for a total of five ions. And because of that I equals five. Now, Covalin compounds are just compounds composed of only non metals together. Okay, we're gonna stay here. That they are. Because of this, they are non volatile. Are you gonna say they are non I in Izabal or non electrolytes? Okay, so here, if they mentioned Covalin salutes, if they mention that they're non volatile, If they mentioned that they are non electrolytes, we group them all under Covalin salutes. So here we have glucose. We have chlorine, we have methanol. And here we have on something called Yuria. So, um, urine, That's one of the main components of it. All of these are co violent in nature, and therefore they are non volatile, which means they don't break up into ions and their non electrolytes, which also means they don't break up into ions. Because of that, I equals one. Now, technically, zero ions are formed, so they just stay in the form that they're in. So that still counts. They stay in the form that they're in. So we just count them as one. So I for them with equal to one. So remember, ionic compounds break up into ions. It's important you get the number correct to write. They'll find the right number for I for co violent salutes. They don't break up into ions there. I will always just be one in its value.
4
example

The Colligative Properties Example 2

clock
1m
Play a video:
Was this helpful?
which of the following compounds will have the largest value for the Van Hoff factor? Alright, So for the first one, we have aluminum chloride, which is composed, which is an ionic compound, so it breaks up into ions. It's composed of one aluminum ion and three chloride ions, So in total, that's four ions. So I equals four for the next one. It's Covalin because only non metals together, So I equals one for the next one. It's ironic again, because zinc is a metal. Oxygen is a nonmetal, so it breaks up into zinc ion and oxide ion. That's two ions total, so I equals two. Next we have ammonia, which is NH three. It's Kovalev because only non metals. So I equals one. And then we have P two s five, which is also Covalin. It's only non metals together, so I equals one. We can see the one with the greatest Van Hoff factor. Value is a I equals four for aluminum chloride. So here the answer would be option a
5
concept

The Colligative Properties Concept 3

clock
1m
Play a video:
Was this helpful?
So remember, for the collective properties, the more salient you add, the more they can be affected. Boiling point and osmotic pressure will keep going up freezing point and vapor pressure would go down. Not the solid amount added equals the number of ions of that salute. Remember that the Van Hoff factor. So that's I times the concentration of that compound or saw it. Now this concentration can represent either molar itty or morality, and for incorporating ions with polarity or morality. Then they become osmolarity and osmolarity. So remember, Osmolarity is ionic polarity. Oz. Morality is ionic morality, right? So for osmolarity saw you formula, we're going to say osmolarity, which is the amount of solute equals I the number of ions for the salute times, the polarity of the compound as a whole. As morality is the same kind of idea, it equals I the number of solute on ions that we have times the morality of the compound. These two formulas will help us determine the amount of solute that a salute given to US represents, and that will help us determine which one to have the highest boiling point, or which one has the lowest freezing point, etcetera. So keep this in mind. We use osmolarity in Oz morality to determine the amount of salt that is at
6
example

The Colligative Properties Example 3

clock
1m
Play a video:
Was this helpful?
What is the Ionic morality of potassium ions in 1.1. A mobile solution. Potassium phosphate. Alright, So we want the ionic morality of potassium ions. Alright, So we're gonna say ionic morality is just osmolarity. So here it will equal the ions of potassium ion times the morality of the compound. If we break this up, it breaks up into three potassium ions, plus one phosphate ion. So how many potassium ions do we have? We have three, So that'd be three times now. The morality of the entire compound is 1.8 mol. So three times 1.18 Molo gives us the Ionic morality of potassium ions. So that will give us option E As our correct answer. So it'll be 3.54 model of potassium ions.
7
Problem

Which of the following compounds will have the highest boiling point?

8
Problem

Which of the following compound will have the highest vapor pressure?

Divider