The Most Delicious Lab of All Time – Freezing Point Depression
So you’re thinking about doing a freezing point depression lab with your students this year and you’re debating between antifreeze and ice cream. Please, go back and read that sentence out loud. I’m telling you right now, there is no decision to make – you’re making ice cream with your students. It’s going to be the second most chaotic day of the school year, coming after Bunsen burner training. You are going to get a sugar headache. Your room will be a mess. But most importantly, your students are going to remember this day for their whole lives.
The preparation of the freezing point depression lab
I don’t know how you go about getting all these things. That is going to depend on your individual situation. I bring the milk and a cooler, and my students handle the rest.
Here is what you’ll need:
- A cooler to store the ice. It should be clean enough that it can get close to food, please don’t borrow a cooler from the biology department.
- Ice and lots of it – you probably have an ice machine in your cafeteria or in a locker room
- Coarse Salt (I used about 20 pounds for 90 kids)
- WHOLE MILK – you need the fat to make this delicious – no word from me on the non-dairy alternative, but I’ll update this post if I hear anything
- Sugar (probably a 5 pound bag)
- Vanilla Extract
- Nesquik (for chocolate!)
- Gallon Bags
- Sandwich Bags
- Bowls
- Spoons
- Tablecloths (if you want a quick clean up method)
- A custodian on call to mop your floor when you inevitably have a spill
Your students should already know that salt is used to drop the freezing point of water. This isn’t a lesson in teaching, this is for application, and snacking, and fun.
To Make it Easy:
This is what you’ll need for every students you have
- A bowl
- A spoon
- 1 cup of milk, remember there are 16 cups in a gallon
- ¼ teaspoon of vanilla extract (I keep a set of measuring cups in my classroom – I’m afraid I’ll forget to bring my own kitchen set, or they will accidentally be thrown out)
- 1 sandwich bag
- 1 gallon bag (you can save these and reuse – cheaper bags tend to rip though)
- Vanilla
- ¼ cup of sugar (this is high)
- Chocolate
- ¼ cup Nesquik
Freezing Point Depression Ice Cream Recipe
Here’s how it’s done
- Fill a gallon bag about ¾ full with ice
- Pour salt all over the ice. Like ALL over it.
- In the sandwich bag add 1 cup of milk and ¼ teaspoon of vanilla extract
- For vanilla add ¼ cup of sugar
- For chocolate add ¼ cup of Nesquik powder
- Squeeze all the air out of the milk bag and zip it shut.
- Put the milk bag in the ice bag. Try to wedge the bag into the middle of the ice
- Shake for 10-15 minutes
If you are interested in cutting back on some ingredients, you can have students pair up and put two sandwich bags in each gallon bag. They can take turns shaking. The bags get VERY cold, so switching off can be helpful. Plus you will save on salt, ice and gallon bags. You can even have them split a sandwich bag. A cup of ice cream is quite a bit! Half a cup would still be fun, delicious, and the amount of learning would be the same!
You’ll know the shaking is done when the milk has firmed up and become ice cream, but this does come down to personal preference. Remove the sandwich bag and give it a rinse with cold water. This will prevent any salt water from dripping on the ice cream. Squeeze the ice cream out into a bowl and decorate with toppings.
Colligative Properties
This lab is perfect to integrate into your solutions unit when you teach colligative properties, or you can do it for Mole Day (read more about that here), or the day before a break, when it’s hard to schedule anything. It’s never a bad time for ice cream! You can find the specific lab form I use with my students here!
I don’t teach the math of colligative properties, just the concepts. This is the reason why my kids don’t have to measure the temperature of the ice and salt mixture, nor measure the salt.
Colligative Properties Lab for Remote Learning
I did this lab with some of my remote students. I simply gave my students a grocery list and told them what they would need. Then I used my Chromebook to show the process and explain how they should carry out the procedure. The kids were able to make the ice cream in their kitchens and had a great time! Some even invited their siblings to make ice cream with them, which simply makes a teacher’s heart glow.
I have hybrid students, that are at school every other day, and I have some remote students. To accommodate all students, I gave two assignments over two days. Because it is the end of our learning unit, the students will do a test on one day, and the lab on the other. The kids that are hybrid will do the lab in school with me. Any students that were full remote could be my virtual lab partner, or do the lab on their own, then do the test the following day. Not ideal, but nothing about remote teaching really is…
PS: This lab is a green chemistry lab, meaning that it doesn’t produce chemicals that are harmful to the environment. Read more about my favorite green chemistry labs here! I don’t often have my students write a lab report for this activity. Because you know, that would put a major damper on ice cream. But if your kids need something academic to justify having this much fun at school (admin probs, I get it) grab a free copy of my lab rubric here.
