Why salty water doesnt freeze

My son performed this experiment for Science class. He used the same plastic cups, cold filtered water from the frig, added a little salt to one cup, placed them in the freezer at the same time and in the same spot.

We checked the cups later about an hour and were surprised in our findings. The fresh water had a little rim of dense ice, with a water temperature of 32F. While the salt water had a much thicker layer of less dense ice, with a water temperature below freezing. My son wrote down that the salt water froze faster than fresh water. He, of course, got a "B" on the assignment because that was not the expected outcome. Can someone please explain what happened? I'll explain what I can, but it's only part of what your son observed.

As each cup was partially frozen, the temperature T was lower in the salty water. That's because salt water freezes at a lower T, as we've explained in other answers on this site.

T doesn't drop much below the freezing T until all the water is frozen. So what your son noticed was the well-established fact that salt lowers the freezing T. The salty water froze faster. That's a little surprising see above but not at all impossible.

I don't know why it happened. One possible reason might be that as the water started to evaporate which it will do a salty crust formed on the edge of the glass. That crust can help wick water up and speed up evaporation. Evaporation itself helps speed cooling. That's why we sweat when it's hot. That's just a guess. The point is that freezing rates are complicated things that can show surprising behavior. The teacher down-graded your son for accurately reporting his observations.

I don't necessarily understand this educational phenomenon either, but when you think of how poorly trained most of the science teachers in the US are, it's not all that surprising. What is the freezing point and boiling point of orange juice? I've marked this as a follow-up to an old question where we discuss a bit of the basic physics. She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter.

Key Takeaways: How Salt Melts Ice Salt melts ice and helps keep water from re-freezing by lowering the freezing point of water. This phenomenon is called freezing point depression. Salt only helps if there is a little bit of liquid water available.

The salt has to dissolve into its ions in order to work. Different types of salt are used as de-icing agents. The more particles ions formed when a salt dissolves, the more it lowers freezing point.

Featured Video. Cite this Article Format. Helmenstine, Anne Marie, Ph. Freezing Point Depression Example Problem. Why Does Salt Melt Ice? Science of How It Works. Properties of Ionic and Covalent Compounds. Pure Substance Definition in Chemistry. Where to Buy Saltpeter or Potassium Nitrate. Boiling Point Elevation Example Problem. How to Separate Salt and Sand — 3 Methods.

Examples of Physical Changes and Chemical Changes. Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo. Thanks for asking, Jaime! Since we do not list the publication date for our Wonders of the Day, you may put the date you accessed this page for information. Also, we ask that Wonderopolis be listed as the author. The following is how you would cite this page:.

Accessed 7 Mar. We love that you love Wonderopolis, Lily!! We also think it's super fun to learn new things!! Hi, Lily! Our Wonderopolis team loves to reply to all of our Wonder Friends!! Interesting question, Toby! We think you might find that answer in the article. If not, let us know! Sorry you didn't find the answer you were looking for, Toby! The article explained how the salt in saltwater can prevent the ocean from freezing. This freezing is what would create more Antarctica, right?

That's your question? You might need to continue on and do a little more research to find the answer to that one. Thanks Zach! Thanks for the shoutout! Thank you for asking, bob! Since we do not list the publish date, you can simply use the date that you accessed this webpage for information. If that was October 15, then use that date. Hey again, nevaeh! You can view standards in MLA formatting for a bibliography by clicking here. We hope that helps! Thanks for asking, ag.

The following is how you would cite this Wonder of the Day. You may use Wonderopolis as the author and since we do not list the publish date, you can use the date you accessed the article for information. Hi, Jazmine! Thanks for sharing your thoughts!

We hope you understand and visit again soon! We hope you're having fun exploring the site and learning lots of new cool things! That is one way to help prevent ice, Jaden! Thanks for sharing! I totally agree Anna, one day, I was doing a article about the internet, and I found this website, and I looked around and looked at all sorts of wonders, I thought I was in heaven for a second, I wish it wasn't winter break so I could share it with everyone!

We're glad you discovered Wonderopolis! We hope you tell everyone about Wonderopolis when you get back to school! Thanks for spreading the word about Wonderopolis! Hopefully when everyone gets back they will tell you more about the Wonders they visited! I'm sorry to hear that this site is a great place to learn interesting facts but if you do not in joy this one find another one.

Thanks for joining the discussion, Jaden! It's nice of you to share your suggestion. We know everyone can find one about something their interested in! We're sorry you're not having fun at Wonderopolis! There are more than 1, Wonders you can explore.

We encourage you to check them out. We know you will find one you like better! That puts a smile on our faces, Anna! We're really glad we have you as a Wonder Friend! Thanks for joining the discussion, Olof! We hope you liked this Wonder. Glaciers and water and freezing-- oh my! Thanks for joining the discussion, Denzel! It does not literally rot. We were just saying that learning it good for your brain and keeps your brain active. Thanks for paying such close attention! We hope you will come back to Wonder with us again soon-- thanks for sharing what you learned today!

That's an awesome thing to know, Wonder Friend Serenity, especially if you live in an area where it snows and ices! It's so great that you learned something new with us today!

That's music to our ears, Wonder Friend Anthony! Thanks for telling us about what you learned today-- we hope you're staying cool after this chilly Wonder! Hey Claudine! Salt is one cool ingredient, if we do say so ourselves! We love WONDERing about how it salt affects the temperature of water and other types of liquids, solids and even food! It sounds like you have learned all about frozen rivers, lakes and ponds today Devon! Nice work! Science is a lot of fun, especially when you can Wonder with your friends!

Thanks for visiting us today! That's awesome, Bradley, we have so many science Wonders to share with you!

We're sorry to hear this Wonder wasn't one of your favorites, Lilly. We Wonder: what's your favorite topic to Wonder about? We're so glad you're here, Ryan! Thanks for stopping by!

We hope your paper is great, and we hope to see you soon, Wonder Friend! Thanks for sharing your comment, Ky Duyen Quang! We're so glad you have a connection to our science Wonder, too! How clever that your family uses salt to melt ice! We're thrilled to be a part of the day! Kilpatrick's 5th grade class! We sure are happy to hear that you learned about the science of water, ice and salt.

Whenever we're extra thirsty, we toss some ice cubes in our glass of water-- so refreshing! We're so glad to hear how much you enjoyed our science Wonder, Morat! Thanks for joining the fun and sharing your comment! We're so glad you learned something new, Gavin! Chemistry is lots of fun to Wonder about! We're glad you enjoyed today's Wonder, Yeniffer, and learned something new, too! Hi there, Cate! Thanks for sharing your awesome comment!

See you soon, Cate! How great, Sheyla! We're so happy to hear that our Wonder goes well with what you're learning in class!

Thanks for sharing your comment, Grace! We sure hope you get to the North Pole, too! Keep up the great work!

Thanks for sharing your comment, GM! We're glad you picked out your favorite part of today's Wonder, we're so glad you are here today! We are undergoing some spring clearing site maintenance and need to temporarily disable the commenting feature. Thanks for your patience. Drag a word to its definition. You have answered 0 of 3 questions correctly and your score is:.

Want to add a little wonder to your website? Help spread the wonder of families learning together. We sent you SMS, for complete subscription please reply. Follow Twitter Instagram Facebook. Does salt water freeze? At what temperature does ocean water freeze? Is polar ice freshwater or salt water?

Wonder What's Next? Hang onto your umbrella! Try It Out Are you up for a swim?