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Salt melts ice essentially because adding salt lowers the freezing point of the water. How does this melt ice? Well, it doesn't, unless there is a little water available with the ice. The good news is you don't need a pool of water to achieve the effect. Ice typically is coated with a thin film of liquid water, which is all it takes.

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

February 1, 2010 at 1:56 pm
(1) Ehsan says:

Thank you,it is very useful.

April 14, 2011 at 10:55 pm
(2) kate says:

why in a ice plant they use salt to prevent the ice to melt ? just asking.

July 19, 2011 at 1:21 am
(3) Coupons says:

Thanks for the write up, I always wondered why Salt melts Ice so easy. Always learning something on the Internet.

February 1, 2010 at 11:21 pm
(4) salam says:

Hi
I certainly feel pleased with your explanation and admire you for the way you put things together.

February 2, 2010 at 11:31 am
(5) Jim says:

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

February 2, 2010 at 7:22 pm
(6) rhianna says:

cool I love it .

October 26, 2010 at 3:30 pm
(7) Ayenaj says:

You aren’t the real Rihanna?

February 5, 2010 at 8:16 am
(8) Abi Legesse says:

It conforts me! You should be happy b/c you are a successful WORLDWIDE Chem. Teacher

February 8, 2010 at 9:12 am
(9) chernet says:

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.

February 20, 2010 at 5:51 pm
(10) Ryan says:

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 ?

May 20, 2010 at 9:22 pm
(11) William Komp says:

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.

June 15, 2010 at 7:12 am
(12) zak says:

thank you! I had a science investigation and u nailed just why I was asking for!

September 24, 2011 at 1:33 pm
(13) Brett Bilgisayar says:

Yes, that is a great idea for a science experiment project for school!

October 12, 2010 at 1:35 pm
(14) Lauren says:

Thanks for answering my homework.

From Lauren+Melissa(:

December 6, 2010 at 12:45 pm
(15) Tinazia says:

wow thanks ummm what are ya’ll talking about?????

January 9, 2011 at 7:21 pm
(16) Jodie says:

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.

January 13, 2011 at 5:29 pm
(17) trisha says:

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?

January 30, 2011 at 11:41 am
(18) joe says:

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.

May 16, 2011 at 8:00 pm
(19) lucy says:

thanks joe for clearifiying! ;]

January 18, 2011 at 10:33 am
(20) berneil cecil says:

thanks for the help i really needed it for my science project

January 20, 2011 at 7:53 pm
(21) megan says:

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?

January 30, 2011 at 11:44 am
(22) joe says:

You should try a mix of calcium chloride and magnesium chloride but it is kind of expensive. Or you could try sand.

January 22, 2011 at 2:56 pm
(23) Mark says:

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.

February 12, 2011 at 1:57 am
(24) ZeroRequiemGX says:

I Actually Understood this

February 25, 2011 at 6:08 pm
(25) C@D!$_EtR@M@_D!_R@!zEL says:

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! :D

April 12, 2011 at 6:11 pm
(26) kenziee! says:

thanks for the Info. helps alot.! i need something EASY to do for my science fair….. thanks again

April 12, 2011 at 6:11 pm
(27) kenziee! says:

thanks for the Info. helps alot.! i need something EASY to do for my science fair….. thanks again

April 12, 2011 at 6:11 pm
(28) kenziee! says:

thanks for the Info. helps alot.! i need something EASY to do for my science fair….. thanks again

August 25, 2011 at 5:46 am
(29) Harshita says:

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

October 1, 2011 at 2:31 pm
(30) nick says:

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. :)

November 4, 2011 at 12:43 am
(31) thx says:

thanks for this.

January 4, 2012 at 7:47 pm
(32) yop-o-let says:

helpful but what damige can it cause to the ecosystem?

January 4, 2012 at 7:51 pm
(33) tomy says:

thanx yo you helpful yo peace out

January 22, 2012 at 1:19 pm
(34) charlie says:

thanks for the info. helped a lot DUDE Rock On

February 7, 2012 at 6:58 am
(35) joel says:

very good u shud use this web site alot

February 26, 2012 at 11:50 pm
(36) Taylor says THANKS says:

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!

February 28, 2012 at 9:29 pm
(37) Jeff says:

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.

March 4, 2012 at 6:59 pm
(38) Brianna Bansraj says:

Thz so much =P

March 12, 2012 at 5:42 pm
(39) Justin Summer says:

thanks SO much this helps me out when im looking for imformation to help me with work! thanks love you bye

March 25, 2012 at 3:58 pm
(40) jay jamez says:

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

April 13, 2012 at 1:24 pm
(41) Shannon says:

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.

May 16, 2012 at 12:52 pm
(42) elizabeth says:

thank you a lot you helped
<3

July 12, 2012 at 11:43 am
(43) Myron says:

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?

July 15, 2012 at 5:34 am
(44) Piros says:

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

October 8, 2012 at 9:58 am
(45) Sarah says:

Overall, good explanation and detail information (:

January 2, 2013 at 1:41 pm
(46) hannah says:

hey! ur site is amazing!!!! but why does ice and salt together hurt your hand?????????

January 7, 2013 at 5:38 pm
(47) khaliah says:

Thanks cuz that help a lot :-)

January 15, 2013 at 9:21 pm
(48) jerry wiley says:

why do u put salt in a home maker ice cream churn

when ur making ice cream why does it make it colder

January 17, 2013 at 3:37 pm
(49) Gabriel Thornton says:

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.

January 26, 2013 at 4:27 pm
(50) Leonard says:

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!

January 27, 2013 at 4:17 pm
(51) Ryan says:

IT WORKS REALLY WELL

January 30, 2013 at 6:02 pm
(52) Jacky the fourth says:

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.

May 27, 2013 at 5:05 pm
(53) ngamoki says:

thank u very helpful

October 4, 2013 at 10:11 am
(54) samle says:

What about ice on an ice cube… And will putting salt on ice melt it quicker?

February 2, 2014 at 3:20 pm
(55) amy says:

so cool thankyou

February 6, 2014 at 9:05 pm
(56) Mike says:

You explained what the reaction is but How and why? What is going on chemically that causes a lower freezing point

March 4, 2014 at 9:12 pm
(57) Rachel says:

This is awsome beacause i am useing this wesite to do my project with salt and ice and you did a very great job :D

March 9, 2014 at 6:02 pm
(58) lady gaga says:

this is soooo helpful omg you made my day. i have been suffering a severe anxiety with this assignment and im lady gaga.

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