effect on boiling point

[inaccensa]

---

Members don't see this ad.

Boiling point of a substance increases with addition of non-volatile substances. Is it safe to say that if the substance added can form strong intermolecular bonds, it will be more effective at raising the bp. In addition, if we are comparing 2 different solutes, does the molecular weight affect the bp. I think that the one with higher molecular weight will raise the bp more effectively.

A question from TPR

Mixing 10g of which of the foll alcohols with 500ml of water will result in a solution with the highest bp.
--ethylene glycol (bp- 197.3C)
--diethylene glycol (bp -244.5C)
--methanol (bp- 64.7C)
--isopropanol (bp-82.3C)

 

[OMTlover]

Boiling point of a substance increases with addition of non-volatile substances. Is it safe to say that if the substance added can form strong intermolecular bonds, it will be more effective at raising the bp. In addition, if we are comparing 2 different solutes, does the molecular weight affect the bp. I think that the one with higher molecular weight will raise the bp more effectively.

A question from TPR

Mixing 10g of which of the foll alcohols with 500ml of water will result in a solution with the highest bp.
--ethylene glycol (bp- 197.3C)
--diethylene glycol (bp -244.5C)
--methanol (bp- 64.7C)
--isopropanol (bp-82.3C)

To be exact. You have to figure out the mole fraction. All solutes are assumed to be non-volatile. The lowest mole fraction will give you lowest lowest vapor pressure and thus highest BP. In this case diethylene glycol and water should give the highest BP.

 

[inaccensa]

To be exact. You have to figure out the mole fraction. All solutes are assumed to be non-volatile. The lowest mole fraction will give you lowest lowest vapor pressure and thus highest BP. In this case diethylene glycol and water should give the highest BP.

The correct ans actually is ethylene glycol

 

[OMTlover]

The correct ans actually is ethylene glycol

Strange. Even if you just look at the # of possible H-bonds, diethylene glycol should still be the choice as it forms max # of bonds with water thus raising BP. 😕

 

[wanderer]

To be exact. You have to figure out the mole fraction. All solutes are assumed to be non-volatile. The lowest mole fraction will give you lowest lowest vapor pressure and thus highest BP. In this case diethylene glycol and water should give the highest BP.

First of all, for the two liquids with a BP below that of water, the liquids have a higher vapor pressure than water, so you can't assume non-volatile. However both will boil below 100 degrees.
For ethylene glycol and diethylene glycol, in the short amount of time that you will have to solve under a timed test, you should assume both have negligible vapor pressure at pure water's bp. If you have 10 g of each, you have more moles of the substance with lower MW. Therefore the ethylene glycol mixture would boil at a higher temp since you have more of it than of diethylene in terms of moles.