# The Naked Scientists Forum

### Author Topic: why does the boiling temp of a solution depend on moles?  (Read 1838 times)

#### thebrain13

• Sr. Member
• Posts: 442
##### why does the boiling temp of a solution depend on moles?
« on: 13/04/2011 01:32:02 »
Pure water at 1 atmosphere boils at 100 degrees celcius. However if you add any solute to the solution whether it is iron or chloride, it raises the boiling point by approximately .51 degrees per mole of solute (as long as it is not an elecroylte). Why? It seems quite random, and disconnected from the logic behind boiling points in general.

#### thebrain13

• Sr. Member
• Posts: 442
##### why does the boiling temp of a solution depend on moles?
« Reply #1 on: 13/04/2011 02:31:55 »
Oh wait a minute, not to be a super lame guy that answers his own questions but I think I figured it out. The reason is because boiling point is defined as the temperature in which the vapor pressure equals 1 atmosphere. I never knew that. Vapor pressure is then based upon the mole fraction of the liquid and the non-volatile solute. Therefore boiling point is a function of the moles of the solute.

And I could see how vapor pressure would be cut down based upon moles, there are more non-volatile(doesnt evaporate readily) particles in the solution preventing it from leaving, whereas those same particles wouldn't stop the particles from the atmosphere from entering.

Again sorry for being so lame [:I]

#### Bored chemist

• Neilep Level Member
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##### why does the boiling temp of a solution depend on moles?
« Reply #2 on: 13/04/2011 06:57:40 »
There's nothing lame about working something out.

#### The Naked Scientists Forum

##### why does the boiling temp of a solution depend on moles?
« Reply #2 on: 13/04/2011 06:57:40 »