[moneyman]

Well, recently, my class did an ice cream lab with plastic bags, ice, and salt. We put the milk and sugar mixture in a bag, then put it in a container filled with ice and salt. After several minutes of shaking, the milk turned into ice cream.
A few things I didn't get was what was happening to the ice and salt during the whole experiment as well as the milk mixture. How did the milk turn into a solid? Was the ice just freezing the milk. If so, why was the salt required.

Also, I have a few questions that I also cannot seem to understand and I have done some searching but to no success.

1. When MgCl2 dissolves in water, how many ions are formed in solution? Also with AlCl3?

2. Why is it that when the vapor pressure of a solution decreases, the solution's boiling point increases.

3.What characteristics of salt would raise the boiling point of water the most? Like for example, if I gave you NaCl, AlCl3, or MgCl2, which one raises the boiling point of water the most.

If anyone can answer these questions (I know they are somewhat lengthy), It would be greatly appreciated. Thanks in advance. George.

[enahs]

I did not read it all, in fact I read very little. And while there is a lot of information here, it appears to cover the bulk of your ice cream questions, with much more information. I would give it a read then again ask about any specific questions.
http://www.foodsci.uoguelph.ca/dairyedu/findsci.html


For your other questions:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch15/colligative.php
Again, I did not read it all, but it seems to cover the bulk of what you are asking.

[moneyman]

Okay, so I kind of skimmed through the page and what I got from it was that salt and ice have to keep getting added so that the ice cream mixture can freeze. But what I'm not sure of is why would salt have to be added to the ice? Wouldn't the salt just melt the ice and make it a lower temperature? What is really the purpose of salt.

[Yggdrasil]

You just answered your own question.  The salt lowers the temperature of the ice/water solution.  For more on the chemistry behind this phenomenon, look up Freezing-Point Depression in your chemistry text or on wikipedia.

El Salvador, please do not insult our members.  moneyman's questions are reasonable questions for someone just starting out studying chemistry (remember this is a HIGH SCHOOL forum).  Consider this a warning, if you continue to make posts which are insulting to others and offer no constructive comments, we will ban you from this forum.

[moneyman]

Well, I do know that the salt lowers the temperature of the ice but what is the point of that? I mean, shouldn't you want the ice to be at it's coldest so that the ice cream will form.

[Yggdrasil]

Salt + ice is colder than ice without salt.

[enahs]

Well, I do know that the salt lowers the temperature of the ice but what is the point of that? I mean, shouldn't you want the ice to be at it's coldest so that the ice cream will form.

Ice is colder then 0^oC (32^oF). Water at normal atmospheric pressure turns to ice at 0^oC. Ice is a solid and not capable of surrounding a container well and efficiently transferring energy in the form of heat. By adding the salt, and lowering the freezing point of water, you make the water colder then 0^oC, and because the water can more effectively surround the container it can better transfer energy in the form of heat. Thus, ice + salt makes colder water then just ice + water, making the solution colder and chilling other things in contact with it faster. Again, these appear to be covered in those links!

[constant thinker]

You'll always meet people in life who think they're better than you because of whatever position they hold. Just ignore them.

I'm sorry you feel that way El Salvador, but some of these topics I truly cannot grasp the content of, and I am sorry to those who tried to help me if you think that I am just looking for an easy way out. To be honest, I did not know where else to look for help, and I felt that this forum had a nice and warm enough community for me to try. Again, thanks for the advice. I'm about to read all these pages that have been posted.

All of the forum regulars and staff will gladly help you. We (the regulars) all understand that people are at different points in their understanding of chemistry, and everyone learns at a different pace. Welcome to the community, and feel free to ask questions.

By the way, obviously El Salvador did not read the forum policy.

"4. Please show that you've at least attempted the problem. We don't mind helping you solve problems but we are ethically opposed to doing homework for you. Violators will have their topic deleted or locked, and subject to banning."

People are constantly warned/told not to post questions without attempting them, and those that do receive no help until they comply with the policy. Usually people just need a nudge in the right direction, or pointed to a good source to solve their problems. Moneyman though is not in violation of this rule.

Now that that's all out of the way...

1. Write out an ionic equation.
Ex. NaCl + H₂O --> Na⁺_(aq) + Cl^-_(aq)
As you can see you have 1 Na⁺ ion and 1 Cl^- atom formed from 1 NaCl. This is 2 ions for every 1 NaCl. That proportion can be applied to any amount in any unit you're given be it moles, grams, liters, etc.
(by the way my example isn't a proper ionic equation, but I feel it gets my point across)

2. Read (which you probably have) about the colligative properties. Enahs gave you a good link.

3. Colligative properties are the best thing to read about here.

If you still have questions feel free to ask.

[Donaldson Tan]

The missing posts in this thread have been moved to the trolling thread.

We have good evidence that both El Savador & Jonathan Dipset are either the same person or representing the same interest. Trolling is not tolerated in this forum.