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Q: EFFECT OF SALT ON FREEZING WATER TEMPERATURE ( Answered,   1 Comment )
Question  
Subject: EFFECT OF SALT ON FREEZING WATER TEMPERATURE
Category: Science > Physics
Asked by: aminah-ga
List Price: $2.00
Posted: 05 Dec 2005 16:26 PST
Expires: 04 Jan 2006 16:26 PST
Question ID: 601907
HOW DOES SALT AFFECT THE TEMPERATURE OF FREEZING WATER

Clarification of Question by aminah-ga on 05 Dec 2005 16:40 PST
will adding salt to freezing water affect its temperature?

Clarification of Question by aminah-ga on 05 Dec 2005 16:42 PST
will salt change the temperature of freezing water?
Answer  
Subject: Re: EFFECT OF SALT ON FREEZING WATER TEMPERATURE
Answered By: juggler-ga on 05 Dec 2005 17:02 PST
 
Hello.

Adding salt to freezing water lowers the temperature at which the
solution will freeze.  In other words, adding salt to ice may make the
ice melt not because the salt raises the temperature but rather
because a new solution is formed that  has a lower freezing point.

See: 

"Pure water freezes at 32 F or 0 C. Salt water freezes at a lower
temperature though, about three or four degrees lower."
source: Re: How does salt affect water?
http://www.madsci.org/posts/archives/feb2001/983550047.Ch.r.html

">Does salt water freeze, if so, at what temperature? Are icebergs fresh
>or saltwater?
Yes, salt water freezes. The temperature at which this happens depends
on the salinity (amount of salt in the water). Ocean water is about
3.5% salt (mostly sodium chloride, just like table salt). At this
salinity, the freezing temperature is about -2 degrees Celsius (about
28 degrees F), so sea water can stay liquid for a little while after
fresh water would freeze."
http://www.seps.org/oracle/oracle.archive/Life_Science.Oceanography/2001.01/000978640429.9691.html

"Water freezes at 32 degrees F. (0 degrees C ) When a compound like
salt is added to the ice, a new solution with a lower freezing
temperature than ice is
formed. This is why salt is added to ice to make ice cream. A common
student misconception is that salt raises the temperature and causes
the ice to melt. In reality a new solution is formed that has a lower
freezing point than ice."
http://www.aea10.k12.ia.us/curr/science/sci4-9/States/STATE690.html


"...salt water freezes at a lower temperature than ordinary water. In
other words, it has to get colder than 32 F (O C) before salt water
will freeze."
http://www.ghbooks.com/activity/activity.cfm?bookid=10015&page=111

"What effect does salt (table salt) water have on ice? Is there a
difference between salt (table salt) water and rock salt used to melt
ice on the roads?
Answer
Salt water freezes at a lower temperature than regular water. Adding
salt water to ice will melt some of the ice as the molecules mix with
the salt solution."
http://www.school-for-champions.com/science/feedback.cfm?topic=Salts#What%20type%20of%20salt%20is%20used%20to%20melt%20ice%20on%20the%20roads

-------------
search strategy:
"salt water freezes"

I hope this helps.
Comments  
Subject: Re: EFFECT OF SALT ON FREEZING WATER TEMPERATURE
From: martinvanleeuwen-ga on 05 Dec 2005 21:24 PST
 
It is a simple experiment. Just try it and you will see that adding
salt to freezing ice, lowers the indicated temperature on a
thermometer. The reason, for as far as I believe, is that salt lowers
the melt point. The ice becomes water, but melting is a process that
takes up heat energy from its surroundings. Therefore, the
surroundings cool down (thermometer indication drops down).

I did the experiment 8 years back on high school (or what we call it
in the netherlands...) and I believe this was the explanation.

Beste regards, Martin

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