Background Info.......back to top
To start, we know that water freezes at zero degrees Celsius, or thirty two degrees Fahrenheit. We also know that when adding a substance to water changes its freezing/melting point. Using information, we figured we could create a fairly accurate hypothesis. We also know that tap water (which is the water we used as a control) is not going to be chemically exact in every cube, therefore creates an uncertainty. We came as close as we can to adding the exact amount of salt/sugar into each cube, and because we couldn’t add the right amount down to the grain, we have yet another uncertainty. Other than these small uncertainties, we believe that our experiment came as close to perfect as we could get.
Review of Literature.......back to top
While searching for related experiments on melting sugar water and saltwater ice cubes, I found various credible
articles. One stated that a mom and her son were doing the same experiment as I am, and their results were the same as what
I got. They posted their experiment on a website at which there was a reply that gave background information to help back
up their results. “Here are some things to consider. (1) Salt is more dense than sugar, so that many more molecules of salt
are present in the same volume (i.e., tsp) as sugar. (2) Not only that, but each molecule of salt dissociates in
water into two ions, each with the ability to lower melting point, whereas each molecule of sugar dissolves without
dissociating. In other words, the same number of molecules salt has twice the capacity to lower melting point as sugar.”
(Morris) I used this information in comparison with my results. I also found a website where a student did a quite similar
experiment and had a professor explain his results. The website included a good amount of information I used to help further
my investigation. “When you dissolve salt, it changes into ions: NaCl ----> Na+ + Cl-, so for every molecule of NaCl you
dissolve, you make two things in solution. This makes the solution as if there were twice as many particles, effectively. So
the freezing point changes twice as much if the number of solute particles is the only important thing! Of course there are
other factors involved, like the charges on the ions above, and the fact that they are atoms and not molecules...but these
only affect how large the effect is, not whether it happens.” (Topper)
Description of Question.......back to top
The question that this lab represents is: If I add various amounts of sugar and salt individually into a
constant amount of water, which solution will melt faster…The tap water? The saltwater? The sugar water? In more detail,
this is asking: If sugar is dissolved into water at different percentages (by volume) of solution separated individually along
with salt dissolved into water, what will be the melting times? Which solution melted the fastest?
Hypotheses.......back to top
(1) If a certain amount of sugar is added to a constant amount of water and frozen, then it will melt faster
than tap water, and slower than saltwater.
(2) If a certain amount of salt is added to a constant amount of water and frozen, then it will melt faster
than tap water, and faster than sugar water.
Bibliography .......back to top
SEPS.org. Science Education PartnershipS. April 3.
<http://www.seps.org/oracle/oracle.archive/Chemistry_and_Physics.K-5/2004.01/001074496231.23749.html>
Ask A Scientist.
<http://www.newton.dep.anl.gov/askasci/chem99/chem99504.htm>
