- Joined
- Jan 30, 2009
- Messages
- 755
- Reaction score
- 6
How does impurities affect boiling points..
Soluble impurites DECREASE Bp and insolubale impurities INcrease bp?????
Soluble impurites DECREASE Bp and insolubale impurities INcrease bp?????
Boiling point and impurity
- Thread starter RedSoxSuck
- Start date
- Joined
- Oct 16, 2007
- Messages
- 4,197
- Reaction score
- 36
I've always been told that impurities always makes bp go up unless you have too much impurity (like half), then the bp starts shifting toward the impurity's bp.
Solubility is a good question. For an insoluable, if you were able to mix it enough to make a colloid, I think the bp will still go up b/c it still affects the vapor pressure. Now, if it's just an insoluable salt sitting at the bottom of your beaker, i dont' think it'll do much. Not sure if it's oil sitting on top of water though.
Anyway, I'm almost sure bp always goes up, but I'd ask a chem prof/teacher or someone else here to make sure.
Solubility is a good question. For an insoluable, if you were able to mix it enough to make a colloid, I think the bp will still go up b/c it still affects the vapor pressure. Now, if it's just an insoluable salt sitting at the bottom of your beaker, i dont' think it'll do much. Not sure if it's oil sitting on top of water though.
Anyway, I'm almost sure bp always goes up, but I'd ask a chem prof/teacher or someone else here to make sure.
- Joined
- Jun 11, 2008
- Messages
- 191
- Reaction score
- 1
Well the formula for bp is +T=kim, right? so the only way that an impurity can DEcrease boiling point is if T is negative (thus adding a negative number to the original T). Molality can't be negative (you can't have a negative number of moles/kg), and i is the number of ions the impurity dissolves into, and k is some constant. None of these numbers can be negative, thus, the quantity (kim) is usually (never say always) positive.
So...similiar to what isoprop said, I'm not sure when the impurity is going to decrease boiling point unless there are A LOT of it. That's just my logic though (I'm not a chem major), ask your prof to be sure, I guess.
Or you can think of it as no matter if the impurity is soluble or not, you're adding more things in, which requires even more heat to break those bonds than if those things weren't there in the first place.
So...similiar to what isoprop said, I'm not sure when the impurity is going to decrease boiling point unless there are A LOT of it. That's just my logic though (I'm not a chem major), ask your prof to be sure, I guess.
Or you can think of it as no matter if the impurity is soluble or not, you're adding more things in, which requires even more heat to break those bonds than if those things weren't there in the first place.
