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General Chemistry

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

14. Solutions

Boiling Point Elevation

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

Boiling Point Elevation Concept 1

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here. We're going to say the phenomenon when adding a sol you to appear solvent results in increasing of the boiling point of the solvent. Remember, the more so 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, we're gonna say normal boiling point, which is BP, And we're going to say here of the solvent. This is the boiling point of the pure solvent before the addition of salute. So before I've added any salute, this is basically the boiling point of the pure solvent. Now, boiling point of solution, we're gonna say BP solution. This is the boiling point of the solvent after the addition of the Salyut remember, solution is when we add Salyut to a solvent. Now, if we take a look at boiling point elevation, remember, it goes up as we have more salute. We have four areas that we need to focus on the first area deals with the boiling point elevation formula here we're gonna say delta t. B. So the change in our boiling point equals I Times, KB Times Lower case M. I is related to our bent Hoff factor. So these are variables we're going to say here that K B is the boiling point constant of our pure solvent in units of degrees Celsius over morality and then lower case M is morality of the solution in moles of solute per kilogram of solvent. Once we've used this boiling point elevation formula and no, it's 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 T B. Now, the solvents that are customarily using questions like this are water, benzene, chloroform or ethanol. Here are their normal boiling points. If we add salute to them, we'd expect their boiling points to be higher than these that are reported here. They're KB values. Their boiling point constants are these values respectively, .51, 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 collective properties now. One last thing. Recall. If a compound is co violent, non volatile or non ionic, meaning non electrolyte, then it's Van Hoff Factor is going to be equal 21. 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.


Boiling Point Elevation Example 1

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Calculate the boiling point of a 3.71 mobile Equus calcium bromide solution. All right, 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 salt of our pure solvent, what exactly is our solvent here? Well, here they're saying, Aquarius, when we say a quick is that means the solvent is water. Pure water boils at 100°C. All we have to do now is figure out what our new changing boiling point will be. So we're gonna say Delta T B equals I times KB times m remember eyes, the number of ions your salute will dissolve into when placed in a solvent. Here, calcium bromide is Ionic. It breaks up into a calcium ion Plus two bromide ions. For a total of three ions. The solvent is water. The boiling point constant of water is .51°C over morality. Then finally, we're gonna say our morality is given us given to us as 3.71 mole, So moralities cancel out and I'll have my answer. Here is degrees Celsius, which comes out to five point 68°C. 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 saw you two are pure solvent here. Pure water was at 100 degrees Celsius. After the addition of calcium bromide, it's now at 105.68 degrees Celsius.

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.


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?  


What is the molality of glucose in an aqueous solution if the boiling point of the solution is 103.15°C?


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?