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Topic: dissociation and boiling points  (Read 7415 times)

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chemicalLindsay

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dissociation and boiling points
« on: June 05, 2004, 03:35:03 AM »
Water has a lower boiling point than salty(table salt) water.The boiling point of water is actually raised by the occurance of hydrogen bonding in the water molecules (dipole dipole interaction) as the water molecules are polar covalent right (I think so).From this and by thinking about the dissociation of salt I came to the conclusion (I didn't read this) that the boiling point of salty water was higher due to the dissociation of salt.I thought this because when salt is dissociated in water Na+ ions and Cl- ions form and are surrounded by the different polar ends of the water molecules (hence the sodium ions being positive are surrounded by the oxygen atoms (vice versa) in the water molecule as oxygen is slightly negative due to the polar bonding).know the electrostatic attraction between two minute charges (hydrogen bonding) is less than the electrostatic attractions between a minutely charged partice and a ion(dissociation) so if you think about it the force holding the water molecules in salty water is greater than the force holding them in just normal water .so it is easier for the water molecules to escape into the atmosphere (evaporate) when it is juat pure water than when the water is salty thus the boiling point of water would be less then the boiling point of salty water.Thanks (correct me if Im wrong)

Offline Donaldson Tan

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Re:dissociation and boiling points
« Reply #1 on: June 05, 2004, 11:57:38 PM »
If you have more particles in your solution, the boilng point would be higher (with reference to Raoult's Law) The mathematical relationship would be:

( T - To ) /  T o directly proportional to n / ( n + ns )

To : Boiling Point of Pure Solvent
T : boiling point of Solution
n : no of moles of solutes
ns : no. of moles of solvent

This applies to non-volatile solutes FYI.
« Last Edit: June 05, 2004, 11:58:49 PM by geodome »
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chemicalLindsay

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Re:dissociation and boiling points
« Reply #2 on: June 06, 2004, 01:33:52 AM »
I understand the more particles in a solution the higher the boiling point as their is more energy required to get the particles vibrating sufficiently (kinetic theory) in order for them to escape the surface and into the atmosphere (This is right isn't it).However wouldn't the forces between the molecules of water and the ions contribute to the higher boiling point as well?
Thanks

Offline AWK

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Re:dissociation and boiling points
« Reply #3 on: June 07, 2004, 01:20:35 AM »
My two cents to this discussion - Raoult's law is accurate only for dilute solutions.
On the possible deviations from this idealised law see:
http://scienceworld.wolfram.com/chemistry/RaoultsLaw.html
« Last Edit: June 07, 2004, 02:02:20 AM by AWK »
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Offline gregpawin

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Re:dissociation and boiling points
« Reply #4 on: June 07, 2004, 01:49:36 AM »
Not to mention for ideal solutions: solutions that have equal attractions/repulsions between the solute and solvent
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