Boiling Point Elevation - Video Tutorials & Practice Problems
Get help from an AI Tutor
Ask a question to get started.
Boiling Point Elevation is the phenomenon when adding a solute to a pure solvent results in increased boiling point of the solvent.
Boiling Point Elevation Calculations
1
concept
Boiling Point Elevation Concept 1
Video duration:
3m
Play a video:
Here we're going to say the phenomenon when adding a solute to a pure solvent results in increasing of the boiling point of the solvent. Remember, the more solute you add, the higher your boiling point will be. Now with this idea of boiling point, we have what's called the normal boiling point and then the boiling point of the solution that's created. Gonna say normal boiling point which is bp and we're gonna say here of the solvent. This is the boiling point of the pure solvent before the addition of solute. So before I've added any solute, this is basically the boiling point of the pure solvent. Now, boiling point of solution, we're gonna say b p solution. This is the boiling point of the solvent after the addition of the solute. Remember, solution is when we add solute to a solvent. Now if we take a look at boiling point elevation, remember it goes up as we add more solute, we have 4 areas that we need to focus on. The first area deals with the boiling point elevation formula. Here we're going to say delta t b, so the change in our boiling point, equals I times k b times lowercase m. I is related to our Bent Hoff factor, so these are our variables. We're gonna say here that k b is the boiling point constant of our pure solvent in units of degrees Celsius over molality, and then lowercase m is molality of the solution in moles of solute per kilogram of solvent. Once we've used this boiling point elevation formula and know its different variables, we then can figure out the boiling point of our solution. Here, we're gonna say the boiling point of solution equals the boiling point of our pure solvent, so this is our normal boiling point, plus delta TB. Now, the solvents that are customary used in questions like this are water, benzene, chloroformarethanol. Here are their normal boiling points. If we add solute to them, we'd expect their boiling points to be higher than these that are reported here. Their k b values, their boiling point constants are these values respectively, 0.51, 2.53, 3.60, and 1.20. No, you don't need to memorize these numbers. These are just different types of solvents that you might see pop up in a question dealing with the colligative properties. Now one last thing, recall if a compound is covalent, non volatile or non ionic, meaning not an electrolyte, then its van't Hoff factor is going to be equal to 1. And so just keep in mind when it comes to boiling point elevation, these are the key areas you need to pay attention to in order to find the boiling point of a solution.
Boiling Point of the solvent will increase with the addition of a solute.
2
example
Boiling Point Elevation Example 1
Video duration:
1m
Play a video:
Calculate the boiling point of a 3.71 mobile aqueous calcium bromide solution. Alright. So they want us to find our boiling point. So remember your boiling point of solution equals the boiling point of your pure solvent plus the change in the boiling point. So the boiling point of our pure of our pure solvent. What exactly is our solvent here? Well, here they're saying aqueous. When we say aqueous, that means the solvent is water. Pure water boils at a 100 degrees Celsius. All we have to do now is figure out what our new change in boiling point will be. So we're going to say delta t b equals I times k b times m. Remember, I is the number of ions your solute will dissolve into when placed in a solvent. Here, calcium bromide is ionic. It breaks up into a calcium ion plus 2 bromide ions for a total of 3 ions. The solvent is water. The boiling point constant of water is 0.51 degrees Celsius over molality. Then finally, we're gonna say our molality is given as given to us as 3.71 molle. So molalities cancel out and I'll have my answer here as degrees Celsius, which comes out to 5.68 degrees Celsius. So we take that and we plug it here. So when we add those together, our new temperature is 105.68 degrees Celsius. Remember, it's called boiling point elevation. We go up as we add solute to our pure solvent. Here, pure water was at a 100 degrees Celsius. After the addition of calcium bromide, it's now at 105.68 degrees Celsius.
3
Problem
Problem
An ethylene glycol solution contains 25.2 g of ethylene glycol (C2H6O2) in 99.5 mL of water. Determine the change in boiling point. Assume a density of 1.00 g/mL for water.
A
18.4°C
B
9.22°C
C
2.08°C
D
0.572°C
4
Problem
Problem
Pure water boils at 100°C. What is the new boiling point of water after the addition of 13.12 g aluminum chloride, AlCl3, to 615 g water?
A
100.25°C
B
100.08°C
C
100.33°C
D
100.16°C
5
Problem
Problem
What is the molality of glucose in an aqueous solution if the boiling point of the solution is 103.15°C?
A
0.15 m
B
0.29 m
C
6.18 m
D
1.6 m
6
Problem
Problem
Carbon dioxide is dissolved in 722 mL of benzene with a density of 1.59 g/mL. What mass of carbon dioxide would you add to make the boiling point of the solution 104.7°C?
A
11 g
B
500 g
C
22.9 g
D
491 g
Do you want more practice?
We have more practice problems on Boiling Point Elevation