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Learning about freezing point can lead to a tasty reward! |
When trying to devise cool activities for my kids, I
generally stick with either a culinary or a scientific theme. This is mostly because cooking and science
are what I know best. But when the
opportunity arises to combine the two in a fun-filled, hands-on, and awesomely
secret educational activity, I do my best to keep from micturating in my
undergarments.
In my experience, the best example of culinary science
fusion involves a lesson on the concept of freezing point, mainly
because the end product of this stealth lesson can be topped with whipped cream
and a cherry. That’s right, I’m talking
about teaching science while making ice cream.
To fully appreciate the culinary chemistry behind this
frozen delight, it’s important to understand the concept of freezing point and
melting point. Simply put, the freezing
point is the temperature at which a liquid freezes and the melting point is the
temperature at which a solid melts. For
most substances, the melting point and the freezing point are the same.
Let’s use water as an example. If water is cooled below 0°C
(32°F),
it will transform into ice. Therefore,
the freezing point of water is 0°C.
However, if the temperature of ice is raised above 0°C,
it will melt. Therefore, the melting
point of water is also 0°C.
HOWEVER, these points can be manipulated. For anyone who lives in an area where winter
happens, you’ve probably seen the massive seasonal salt inventory at The Home
Depot. The idea is that by putting salt
on walkways, usually in the form of either rock salt (NaCl) or calcium chloride
(CaCl2), you will prevent the build up of ice and snow and thus
prevent any nasty slips. This is because
salt will lower the freezing point of water, thereby helping to keep it from
turning into an icy mess, even when temperatures are below freezing. But, it will only work if the walkway is
warmer than -9°C (or 15°F).
How does this relate back to ice cream? Well, we can use the same idea of lowering
the freezing point of water and apply it to making cream freeze. The set-up involves two resealable plastic
bags (one quart-sized and one gallon-sized), ice, lots of salt, cream, milk,
sugar, vanilla, and your flavoring of choice.
Into the quart-sized resealable plastic bag, combine the
cream, milk, sugar, vanilla, and flavoring (follow the recipe below and ensure
that the bag is fully sealed). Fill the
second resealable plastic bag about halfway with crushed ice and all of the
salt. Place the cream-filled bag into
the ice-filled bag and seal. Then…shake!
When salt is added to the ice water, the temperature of the
mixture drops. Because the temperature
of the ice-salt mixture is lower than the cream mixture, a temperature gradient
is created and the cream mixture easily freezes. After about five to ten minutes of shaking,
you will have yourself some fresh-churned sciencey deliciousness! Enjoy!
Science Experiment
Ice Cream:
½ Cup Heavy Cream
½ Cup Milk
¼ Cup Sugar
¼ Tsp. Real Vanilla Extract
Crushed or Shaved Ice
1 Cup of Table Salt or Sea Salt
1 Quart-Sized Ziploc Bag
1 Gallon-Sized Ziploc Bag
Here is a video of my and a few of my pals doing this
experiment with my daughter. We did this
last year and my daughter STILL talks about it!
The set-up:
The set-up:
Shakin' it up:
The big reveal:
For more information
check these out:
General Chemistry Online Why does salt melt ice?
Sciencebase Salt lowers the freezing point of water
Jeanne Garbarino, Double X Science Editor
The videos are private. I can't watch them. :-(
ReplyDeleteDrysh, sorry about that! It should be fixed now...
ReplyDelete