My name is Amber and I am a full-time volunteer for Science Buddies in software development.
The freezing point is when liquid water and ice are at equilibrium (as ice forms, the temperature does not change until all the water has become ice).
Salt lowers the freezing point because it disrupts the crystallization of water into ice, so you can think of it as the water needs to be colder in order to form ice because the salt acts as a barrier towards forming ice.
We use "freezing point depression" for lots of things. Salt is put on icy roads to "melt" the ice (it forces the water to freeze at a lower temperature). You also use salt when you make ice cream.
Sorry nobody answered your questions by your due date. In the future, keep in mind that we generally do not answer background research questions (unless you've tried your best to answer the question and are confused about a specific concept). Also, post your questions at least a few days before your due date. Experts try to answer questions within 24-48 hours, but that doesn't always happen. See the following rules for interviews (and give them to your teacher, along with the information below):
https://www.sciencebuddies.org/science- ... =28&t=5681
Next time for interview questions, please do not post background research questions about your project (examples of background research questions are: "How do you make chocolate?" "Why do plants need the sun to survive?" "How does an electric motor work?"). It is your job to try and answer such questions by doing your own research. Interview questions should be about the expert being interviewed, not questions you want to have answered about your project. Examples of good and relevant interview questions are: "How long have you worked in this field?" "Why did you become a scientist?" "What do you like most about being a biologist?" "I think my project is useful and important because [discuss why you think it is useful]. Do you agree?"
If you are having trouble finding a resource to answer a background research question, or you don't understand a particular concept, it is perfectly fine to ask a more specific question AFTER doing your best to figure it out on your own, but such questions still do not make good interview questions (please put them in a different post under the same topic).
If your teacher told you to ask this type of interview question, let them know that they need to change their instructions for next year, and give them the above information. Thanks!
I hope your project turned out well!