Pure water freezes at 32°F (0°C). Water with salt (or any other substance in it) will freeze at some lower temperature. Just how low this temperature will be depends on the de-icing agent. If you put salt on ice in a situation where the temperature will never get up to the new freezing point of the salt-water solution, you won't see any benefit. For example, tossing table salt (sodium chloride) onto ice when it's 0°F won't do anything more than coat the ice with a layer of salt. On the other hand, if you put the same salt on ice at 15°F, the salt will be able to prevent melting ice from re-freezing. Magnesium chloride works down to 5°F while calcium chloride works down to -20°F.
Use Salt to Melt Ice - Activities
You can demonstrate the effect of freezing point depression yourself, even if you don't have an icy sidewalk handy. One way is to make your own ice cream in a baggie, where adding salt to water produces a mixture so cold it can freeze your treat. If you just want to see an example of how cold ice plus salt can get, mix 33 ounces of salt with 100 ounces of crushed ice or snow. Be careful! The mixture will be about -6°F (-21°C), which is cold enough to give you frostbite if you hold it too long.
Comments
Thank you,it is very useful.
why in a ice plant they use salt to prevent the ice to melt ? just asking.
Thanks for the write up, I always wondered why Salt melts Ice so easy. Always learning something on the Internet.
Hi
I certainly feel pleased with your explanation and admire you for the way you put things together.
One of my “prized” students took an ice cube and put it on his already salted hand. Wow this never happened before!!My principal got a call and was quick to come to my classroom and tell me. Mom was upset with the teacher for teaching this sort of thing. I think the principal sided with the parent, but who cares she was terminated the next year and I taught for 37 years. The subject was Earth Science and we were studying the freezing point of water and how to change it.
Your sit is SUPER, thanks
cool I love it .
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It conforts me! You should be happy b/c you are a successful WORLDWIDE Chem. Teacher
Above all i appreciate your generousity to share all you have with others for free. You make me love chemistry more.I learn alot from your website. I could see chemistry is all rounded practical subject.
Very nice! I’ve been trying all day to figure out how cold salt can make ice melt.
Just one question… how can salt+ice @0F do nothing at all and yet salt+ice @15F makes brine @-6F ?
It has been a puzzling thing to me how salt can melt ice. But with your detailed explaination it has enlightend my insights of the chemistry of salt and ice.
thank you! I had a science investigation and u nailed just why I was asking for!
Yes, that is a great idea for a science experiment project for school!
Thanks for answering my homework.
From Lauren+Melissa(:
wow thanks ummm what are ya’ll talking about?????
I don’t understand one thing: if adding salt to ice causes a freezing temperature depression which keeps the water from the melting ice from refreezing, then why is it that the experiments show that adding salt to ice seems to make the ice colder (say, cold enough to freeze milk into ice cream). How can the same effect that causes the freezing of ice cream also be used to keep roads and side walks ice free during winter? Seems paradoxical.
Ok i have a question how dose the salt melt the ice? I mean I know it makes the temp higher. But how dose it do that?
Salt does not raise the temperature of ice. The sodium chloride molecules(salt) break apart and bond with the H20 molecules by getting in between the strong hydrogen bonds which lowers the freezing point because it is no longer pure ice. With more salt, the freezing point goes down for the ice.
thanks joe for clearifiying! ;]
thanks for the help i really needed it for my science project
im doing this project for my schools science fair and im experimenting with alcohol , table salt, and road salt so i can compare the effects of each but i think i need one more substance to experiment with/ is there anything else that lowers the freezing point of water / or is there something that maybe i could use that probably wont work but would have been a good guess?
You should try a mix of calcium chloride and magnesium chloride but it is kind of expensive. Or you could try sand.
Why not just try heat? Maybe a blow dryer, heat gun or hot pan could be the source? Just a suggestion. Please be careful and if young have a parent with you.
I Actually Understood this
thank you for the info, but i wish you explained a bit more how the salt drops the temperature of the ice but the ice actually melts,, i still don’t get how that happens.. but putting that aside, this was a very useful information!
thanks for the Info. helps alot.! i need something EASY to do for my science fair….. thanks again
thanks for the Info. helps alot.! i need something EASY to do for my science fair….. thanks again
thanks for the Info. helps alot.! i need something EASY to do for my science fair….. thanks again
Thanks for the information because i had to research about what happens if we put salt in water and put one ice cube.
Thanks for the info
I have a coursework on this subject. Does anyone actually know exactly how the change in state of the water (when sodium chloride dissolves in it) makes the melting point higher? I mean in terms of chemical composition and all that stuff.
thanks for this.
helpful but what damige can it cause to the ecosystem?
thanx yo you helpful yo peace out
thanks for the info. helped a lot DUDE Rock On
very good u shud use this web site alot
I would like to say your a LIFE SAVER! i needed this answer for my science fair question called ” how would salt melt ice?” Thanks soo much! keep on posting!
If ice is kept in a freezer at 0 degrees F why doesn’t it freeze water when I add it to water that is 32 degrees F.
Thz so much =P
thanks SO much this helps me out when im looking for imformation to help me with work! thanks love you bye
this is very worth it thanx for helping me with this because i neded this 4 my science fair project n i never did it n its ue tomoro so thax 4 ur timeand thnx 4 ur help BI, ,BI
I brought up this question in a family discussion, and none of us knew the answer. Thank you for explaining it so clearly and understandably; you’ve helped a lot.
thank you a lot you helped
<3
So actually the salt doesn’t melt the Ice as you said it just keeps the water from refreezing at the surface of the meting ice. Correct?
I thought that ice would dissolve salt since water dissolves ice but meh po-ta-toe po-tah-to
anyway thanks for the explanation easy to understand
-Piros
Overall, good explanation and detail information (:
hey! ur site is amazing!!!! but why does ice and salt together hurt your hand?????????
Thanks cuz that help a lot
why do u put salt in a home maker ice cream churn
when ur making ice cream why does it make it colder
Very useful thanks. Could you put the degrees celcius for all of the examples please as it would make it easier to understand what you are saying. Thanks.
Thanks for the desciption. I am doing a science fair project and it really helped me a lot. On my project, I am tryinf to see if other things beside salt, like flour and sugar, can melt ice easily, too. Thanks again by the way!
IT WORKS REALLY WELL
i am trying to find out that if can melt its that i need it for a project but that was also really useful because i like to read but the stuff that i want to read not just something i don’t
want to read about but i still liked it and i learned more thanks for every thing because if it wasn’t there then i would be so board and nothing to do right now.