Done a post on the Mpemba Effect, where hot water freezes faster than cold under certain circumstances? Fascinating in and of itself, and also curious because while people have been making practical use of it for thousands of years (Aristotle mentions it) science dismissed it as “impossible” until 1969. I find it astounding, though I am easily astounded: “Constant incredulity is the only non-contrived response to life.”
hi i wonder if you could help me answer this question, “why does salty water have a slightly higher boiling point than normal water”? i have tried to find this out by looking on the google site but keep getting all the blurb I cant understand. i’m 9 years old and they confuse me.
Water is a special liquid because the strong oxygen “pulls” electrons from the hydrogen atoms, leaving the hydrogen atoms slightly positive and the oxygen atom slightly negative. These slight positive and negative charges line up (opposites attract) and thus water molecules stick together.
To boil, water molecules need to separate to become a gas. Heat works by pushing energy into the water, forcing the weak bonds between molecules to break, allowing them to float off as gas (steam).
When you add salt (sodium chloride) to water, it separates into sodium and chloride giving a strongly positive sodium ion and a strongly negative chloride ion. Since water has a slight charge, the central (negative oxygen) is attracted to the sodium ion and the ends (positive hydrogen) are attracted to the chloride ions. This attraction is stronger than the attraction between water molecules.
This means that more energy (and more heat) is required to break apart the molecules in the liquid to allow them to float off as gas.
Thus salt water will boil at a higher temperature than plain.
7 Comments
October 29, 2006 at 6:03 am
Very cool – a lot of effort here. And diligent footnotes as well.
November 12, 2006 at 1:26 am
Done a post on the Mpemba Effect, where hot water freezes faster than cold under certain circumstances? Fascinating in and of itself, and also curious because while people have been making practical use of it for thousands of years (Aristotle mentions it) science dismissed it as “impossible” until 1969. I find it astounding, though I am easily astounded: “Constant incredulity is the only non-contrived response to life.”
Doug
November 19, 2006 at 3:07 am
Hmm… that reminds me of something interesting I read the other day about water crystallisation. I’ll check into it some more.
Were you saying you had written a post? Or you would like me to write one?
November 19, 2006 at 12:38 pm
I was suggesting it as a topic for you to blog upon.
Curious what you think. LOL Love the “Cousin It” pic btw. —Doug
November 19, 2006 at 4:49 pm
I think it’s the best photo ever taken of me
I did search your blog in case you had written about it previously.
Thanks for the suggestion – I’ll do some research!
May 3, 2007 at 8:59 pm
hi i wonder if you could help me answer this question, “why does salty water have a slightly higher boiling point than normal water”? i have tried to find this out by looking on the google site but keep getting all the blurb I cant understand. i’m 9 years old and they confuse me.
thanks
molly K
May 5, 2007 at 2:19 am
Hi Molly,
Water is a special liquid because the strong oxygen “pulls” electrons from the hydrogen atoms, leaving the hydrogen atoms slightly positive and the oxygen atom slightly negative. These slight positive and negative charges line up (opposites attract) and thus water molecules stick together.
To boil, water molecules need to separate to become a gas. Heat works by pushing energy into the water, forcing the weak bonds between molecules to break, allowing them to float off as gas (steam).
When you add salt (sodium chloride) to water, it separates into sodium and chloride giving a strongly positive sodium ion and a strongly negative chloride ion. Since water has a slight charge, the central (negative oxygen) is attracted to the sodium ion and the ends (positive hydrogen) are attracted to the chloride ions. This attraction is stronger than the attraction between water molecules.
This means that more energy (and more heat) is required to break apart the molecules in the liquid to allow them to float off as gas.
Thus salt water will boil at a higher temperature than plain.
I hope this makes sense