Melting Ice With Household Substances

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					                                      Melting Ice With Household Substances
Group Members:
Jenny Richardson
Angela Vitale
Meghan Bagby
Kira Hedrich

Grade Level: 7th-10th Grade
Subject: Chemistry
Unit: Thermodynamics
Topic: Freezing Point Depression
Activity: Melting Point of Ice

Introduction:
Freezing-point depression describes the phenomenon in which the freezing point of a liquid or solvent is
depressed when another compound, a solute, is added. This means that a mixed solution has a lower freezing
point than a pure solvent. This happens whenever a solute is added to a pure solvent, such as water. The
phenomenon may be observed in sea water. The salt in the water acts as the solute in this case. Due to the
salt content in ocean waters, the ocean waters stay liquid at temperatures below 0 °C, the freezing point of
pure water.

You are a scientist working at Thermo Labs in Northern Illinois. Winter is coming up, and you have been
commissioned by the city to find out what would be the most efficient in melting ice off the streets, and off of
peoples driveways. You have gathered several different substances to test: calcium chloride, sodium chloride,
sugar, baking soda, and Tide Powdered laundry detergent. After observing the characteristics of each
substance, you need to determine your hypothesis, and test that hypothesis.

Question:
What is the most effective household substance at lowering the melting point of ice?

Hypothesis:
If rock salt (calcium chloride) has the largest crystal size, then it will be the most efficient at melting ice.

Objectives:
   1. Demonstrate proper scientific methods in a lab setting.
   2. Choose a hypothesis and decide how to test that hypothesis.
   3. Discover the topic of thermodynamics.
   4. Compare and contrast pure and mixed substance melting points.




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Materials:
12- Styrofoam cups
1- 50 mL graduated cylinder,
4g calcium chloride (Rock Salt)
4g sugar
4g sodium chloride (Table Salt)
4g Tide powder detergent
4g baking soda
600 mL of tap water left out to degass for two hours.
12- thermometers,
Roll of Aluminum Foil
Stop Watch
Scale
10- Weigh Boats
5- Scoops
Trays--For each group
1- Permanent markers
Freezer
Roll of Masking Tape

Prep:
A few days before the lab, create enough 50 mL blocks of ice for each group of students to have 6 blocks. This
can be done through the following steps:

   1. Using a 50mL graduated cylinder, measure out 50 mL of deionized water. Pour water into one of the
      Styrofoam cups.
   2. Place a thermometer in each cup and tape it to the side to hold it in place.
   3. Place an aluminum foil cap over each cup. The thermometer should poke through the aluminum foil.
      Make sure there is enough aluminum foil to cover the entire opening.
   4. Repeat this for all of the all 6 cups.
   5. Carefully move the cups onto a metal tray for placement in the freezer. Carefully move the tray into
      the freezer and keep in freezer until it is time for the experiment.


On the day of the experiment prepare the substances to be tested.

   1. Label each weigh boat with a permanent marker with the substance that will be going into to it.
   2. Using a weigh boat, measure out 2 grams of each substance. Make sure first place the weigh boat on
      the scale and then tare (or zero) it out.
   3. Using a tray carry the samples to your work area.

Purpose:
The purpose of this experiment is to find out which household items melt ice the quickest based on the
colligative property of water that causes freezing point depression.




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Procedure:
Observe the different samples. Take a look at the different characteristics of each, including the size of the
crystals, their color, texture, etc. Come up with a hypothesis based on your observations as to which
substance will melt ice most effectively.
    1. With a permanent marker, label each of the cups in the following way: Control, rock salt, table salt,
        tide powder detergent, baking soda, and sugar. You will be doing two separate trials so label
        accordingly (i.e Control 1, Control 2, etc...).
    2. After labeling each of the cups, place each sample in its corresponding cup. Make sure the sample is
        distributed evenly over the ice block. This can be done by lightly shaking the cup. This is important for
        getting correct results.
    3. Have one of the group members start the stopwatch
    4. After 30 seconds, 60 seconds, 3 minutes, 5 minutes, 7 minutes, 10 minutes, 15 minutes, and 20
        minutes, and have one person record the temperatures of each cup into the data table.
    5. When you have finished recording all the results, clean up the experiment. Empty the contents of the
        cups into the sink, and place the cups into the trash. Wipe down your table with provided cleaning
        materials.

Data:
Trial 1:
           CONTROL        ROCK SALT        TABLE SALT         SUGAR       TIDE       BAKING SODA
           (°C)           (°C)             (°C)               (°C)        (°C)       (°C)
 INITIAL              2                1                 -2           1          1                 3
 0.5 min              2                2                -12           1          1                 3
 1 min                2                2                 -7           1          1                 4
 3 min                2               -1                 -5           2          1                 4
 5 min                2               -2                 -3           2          1                 4
 7 min                1               -3                 -4           1          1                 3
 10 min               1               -3                 -5           1          1                 2
 15 min               1               -5                 -6           1          1                 2
 20 min               1               -6                 -6           1          1                 2




                                                                                                                    3
                              Trial 1: Freezing Point Depression of Household
                                                  Substance
                        6

                        4

                        2

                         0
                         INITIAL 0.5 min 1 min     3 min   5 min   7 min 10 min 15 min 20 min             CONTROL (°C)
   Degrees (Celcius)




                        -2
                                                                                                          ROCK SALT (°C)
                        -4                                                                                TABLE SALT (°C)
                                                                                                          SUGAR (°C)
                        -6
                                                                                                          TIDE (°C)
                        -8                                                                                BAKING SODA (°C)

                       -10

                       -12

                       -14
                                                 Time (seconds and minutes)




Trial 2:

                             CONTROL        ROCK SALT           TABLE SALT         SUGAR       TIDE       BAKING SODA
                             (°C)           (°C)                (°C)               (°C)        (°C)       (°C)
 INITIAL                                3                   3                 -2           1          3                      0
 0.5 min                                3                   3                 -3           1          3                      1
 1 min                                  2                   1                 -3           1          3                      1
 3 min                                  2                  -1                 -2           1          3                      1
 5 min                                  3                  -2                 -4           0          2                      1
 7 min                                  3                  -3                 -5           1          2                      1
 10 min                                 2                  -3                 -5           1          3                      1
 15 min                                 3                  -5                 -5           1          3                      1
 20 min                                 2                  -5                 -5           1          3                      1




                                                                                                                                 4
                             Trial 2: Freezing Point Depression of Household
                                                 Substance
                       4

                       3

                       2

                       1
                                                                                               CONTROL (°C)
   Degrees (Celcius)




                        0
                                                                                               ROCK SALT (°C)
                        INITIAL 0.5 min 1 min   3 min   5 min   7 min   10 min 15 min 20 min
                       -1                                                                      TABLE SALT (°C)
                                                                                               SUGAR (°C)
                       -2
                                                                                               TIDE (°C)
                       -3                                                                      BAKING SODA (°C)

                       -4

                       -5

                       -6
                                                   Time (minutes)


Results:
For Trial 1 (Graph 1), Table Salt reached the lowest temperature at -12°C, followed by Rock Salt, which
reached a low of -6°C. Table Salt had a temperature range of -2°C to -12°C, finally settling at -6°C with Rock
Salt. Table Salt maintained the range of -3°C to -6°C for the last fifteen minutes of the trial. The remaining
household substances for Trial 1 (Graph 1) maintained relatively constant temperature ranges. Tide had a
remarkably stable range of 1°C, tied only with the Control which also maintained the range of 1°C. Baking Soda
held a range of 3-4°C over the entire twenty minute period. Sugar held a range of 1-2°C.

For Trial 2 (Graph 2), Rock Salt steadily decreased from 3°C to -5°C, staying perfectly within the range of -3°C
to -5°C from the seven minute mark to the twenty minute mark. Table Salt maintained the lowest range from -
2°C to -5°C, staying constant at -5°C for the last thirteen minutes. The remaining household substances for
Trial 2 (Graph 2) again held relatively constant temperature ranges. Tide held a range of 2-3°C over the twenty
minute period. The Control maintained a range of 2-3°C, and Baking Soda held the range of 0-1°C. Sugar had a
range of 0-1°C for Trial 2.



Discussion:
We expected the results of our experiment to show the colligative properties of water. Since one such
property is freezing point depression, we expected to see the solute that dissociates into the highest number
of ions lower water’s freezing point the most effectively. Rock salt was the solute we expected to see act in
                                                                                                                  5
this manner because calcium chloride breaks up into 3 ions. In our experiment, we observed a consistent
drop in temperature over time with the rock salt and ice solution. As shown on the graphs of trial 1 and trial
2, rock salt effectively lowered the freezing point of water to- 5 and -6 degrees Celsius, respectively. However,
rock salt did not drop the temperature in the shortest amount of time during trial 1. As seen in trial 1, table
salt, which dissociates into only 2 ions, depressed the freezing point by 10 degrees Celsius in the first 30
seconds of the experiment. Trial 2 followed our expectations by the rock salt depressing the freezing point by
4 degrees Celsius over the first 3 minutes, and 8 degrees Celsius overall.

As mentioned above, table salt also lowered the freezing point of the water substantially. The large drop seen
in trial 1, suggests the speed at which table salt dissociates in water. Since freezing point depression requires
the addition of ions to the solution, table salt clearly achieves this very quickly. Based on these results, it may
be a fair question to ask why we don’t use table salt on our driveways. We believe the answer to be in
consistency, or lack there of. As seen in both trials, table salt initially reduced the freezing point, but then
raised the temperature of the solution. Following the rise, the temperature falls again, and finally appears to
level off. Further testing would be necessary to see if the inconsistent pattern of table salt we observed is a
common occurrence. If this were found to be true, we can readily see why the rock salt consistently
depressing the freezing point would be desired.

The other solutes that we added to our water (ice) solvent (sugar, Tide, and baking soda) did not show a
depression of the freezing point of water. In both trials we did not observe any of these solutes depressing
the freezing point below 0 degrees Celsius. By the end of trial 1, baking soda had depressed the point by 1
degree, however there was no observed temperature change in trial 2. Sugar caused the temperature of the
solution to fluctuate insignificantly, as the temperature never went below the starting temperature. Tide
showed no fluctuation in trial 1 and slight, insignificant fluctuation in trial 2. These results suggest that the
specified solutes do not dissociate in water, and thusly do not depress the freezing point of water (i.e. melt
ice).

Conclusion:
We were not expecting the results we obtained from table salt, so we are unable to accept our hypothesis
without further testing. While it is highly likely that our hypothesis will be verified as the best solute for
melting ice, it must first be established that table salt does indeed lower the freezing point inconsistently. 1
gram of solute was used per 50 milliliters of solvent in our experiment, but a different ratio may provide more
conducive results. For example, future testing may include 1 gram of solute to only 30 milliliters of solvent.
Comparing table salt and rock salt over a larger span of time may also be informative. Our experiment
consisted of 8 intervals over the course of 20 minutes. Further testing may include more intervals over a
longer period of time.

From a pedagogical perspective, our group decided we would have our students perform this lab with only 30
milliliters of water, instead of the 50 milliliters that we used. We suspect that this would produce more
significant results for the students to analyze. This lab serves as a method for turning an abstract concept such
as freezing point depression into a concrete learning experience for the students. They are provided with
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knowledge that is relative to their lives in and out of the educational realm. In addition, materials and costs
that are required to complete this experiment were minimal and easy to obtain.

References:
Bodner Research Web. [On-line]. Retrieved on March 2, 2010. Available:

       http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch15/colligative.php




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