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Does Salt Effect The Freezing Point of Water?

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by

Danielle Ferretti

on 14 April 2014

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Transcript of Does Salt Effect The Freezing Point of Water?

Does Salt Effect The Freezing Point of Water?
Transition Phase
(without salt)
This diagram represents molecules of water escaping from the solid ice into the liquid water, which is the melting taking place. The molecules of water in the liquid are being captures on the surface of ice, freezing. The amount of water will not change. Freezing is occurring at the same time as melting.
Transition Phase
(with salt)
As ice melts, it gets energy from the surrounding liquid, and the liquid cools. Eventually, the temperature calls to make the water molecules slow down enough enough so that more can attach themselves to the ice.

The higher the concentration of salt, the lover the temperature of the new freezing point.
Chemistry:
the effects of salt on the freezing
point of water
At the freezing temperature of pure water, molecules enter and leave the solid at the same rate. However, adding salt to the mixture disrupts this.


My Hypothesis
Under normal conditions, water freezes at 0 degrees Celsius or 32 degrees Fahrenheit. However, by adding salt, the water will cause the freezing point to become lower. I believe this to be true because in the winter, I place salt on my stairs to prevent ice from forming. In addition, many roads are treated with salt based mixtures as well.

by
Danielle Ferretti
EDT 663: Field Study & Report
Spring 2014
Salt disrupts the equilibrium by being present. When salt is added, less water molecules are present during the change from liquid to solid. Salt molecules block the water molecules from re-entering the solid phase so more water molecules are leaving and less are entering the solid phase.
As temperature continues to decrease, water molecules will eventually match the rate that they can find the solid in the presence of salt, however until then, the freezing point will be lowered. When this occurs, a new (lower) freezing point will be established.
This does not continue
forever! Eventually, the solution will become saturated with salt.
This happens at -21.1 degrees Celsius,
which is the coldest salt water can get.

Evidence: The Ocean
Evidence: Winter Roads
Evidence: Making Ice Cream
My Experiment:
Materials

2 plastic Bottles
2 Tablespoons salt
Water
Freezer
Watch this short video to help understand why oceans do not freeze and
how salt effects this.
Join Bill Nye the Science Guy, to make a tasty treat with stuff you already have at home in your kitchen!
Interesting. However salt only works up to a certain temperature. If it is too cold, it will no longer work.
Procedure:
Fill bottles up with water
In one bottle, place 2 teaspoons of salt
Leave other bottle without salt
Place in freezer for 3 hours, then check.
Re-Check until first bottle freezes.
This is a representation that the salt water took twice as long to freeze in the bottle than the regular water.
Results:
Lets take a look into some facts to support these findings...
The water with the salt in it took longer to freeze because it needed to reach a colder temperature.
Salt water takes longer to freeze than regular water.
The freezing point of salt water is lower than the freezing point of regular water.
Conclusions:
References

http://www.sci-experiments.com/ice_cream/saltwater.html
http://www.scientificamerican.com/article/why-do-we-put-salt-on-icy/
http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml
Full transcript