Name: Miranda Gutierrez
Date: September 26, 2020
Student Exploration: Freezing Point of Salt Water
Vocabulary: freeze, freezing point, liquid, melt, melting point, solid, transformation rate
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. In the winter, people often buy large bags of rock salt to sprinkle on their walkways. Why do
people do this? People buy large bags of rock salt to sprinkle on their walkways because it
helps to melt the ice on the roads and driveways.
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2. The freezing point of pure water is 0 °C (32 °F). How do you think adding salt to water
.
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res ource
affects its freezing point? I think adding salt to the water is going to change the temperature
at which it freezes or boils, therefore adding salt to the water will aff ct the freezing point.
Gizmo Warm-up
People often use salt to alter the freezing point of water.
The Freezing Point of Salt Water Gizmo shows you how
this works.
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1. With the Room temp. set to 0.0 °C, observe the water
molecules in the Molecular view. Describe the motion
of water molecules in the liq id phase:
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The water molecules appear to be br efly bouncing off
each other, almost looking as if they are vibrating.
This
2.
3.
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Set the Room temp. to -10.0 °C and observe. What is happening?
The water molecules have turn solid and vibrate more vigorously. The water molecules
are slowly freezing going down.
The process of c anging from a liquid to a solid is called freezing .
Describe the motion of molecules in a solid: The motion of molecules in a solid vibrate
but do not move from place to place.
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2019
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Activity A:
Get the Gizmo ready:
Freezing point
depression
Click Reset.
Set the Room temp. to 5.0 °C.
Question: How does salt affect the freezing point of water and the melting point of ice?
1. Observe: With the room temperature at 5.0 °C, the water should be in a liquid state. Lower
the Room temp. one degree at a time until the water first starts to freeze. Look at the
thermometer inside the container of water
A. What is the freezing point of pure water? -2.0 degrees Celsius
B. Lower the Room temp. a few more degrees. What do you notice about the water
temperature as the water is freezing?
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.
C. Lower the Room temp. to -10.0 °C, wait until all the water has frozen, and then wait
The ice temperature drops after all the water is froz n.
The larger the room temperature decreases the faster the water molecules will
a little while more. What happens to the ice temperature after all the water is frozen?
freeze.
2.
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Predict: How do you think adding salt will affect the freezing and melting points of water?
By adding salt, it would disrupt the rate at which molecules enter and leave the solid at the
same rate.
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Experiment : Click the
3.
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Add 50 g button to add 50 grams of salt to the water.
Lower the
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Room temp. to -10.0 °C and observe
the temperature as the water freezes.
What is t e freezing point of this salt solution? -0.3 degrees Celsius
4.
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The ice particles move
Observe: Look for t salt particles in the ice. What do you notice?
the salt particle down as they freeze.
D. Now raise the Room temp. back to 5.0 °C and observe the thermometer inside the
container. At what temperature does the ice melt? This is the melting point of ice.
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3.2 degrees Celsius
(Activity A continued on next page)
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2019
https://www.coursehero.com/file/69624229/Freezing-Point-of-Salt-Water-docx/
Activity A (continued from previous page)
5. Experiment: After the water has completely frozen, raise the Room temp. to 5.0
°C. Observe the water temperature as the ice melts.
What is the melting point of this salt solution? 2 degrees Celsius
6. Collect data: Use the data you have collected so far to fill in the first two rows of the table
below. Then, find the freezing and melting points of water with 100 grams of salt.
Amount of salt (g)
Freezing point (°C)
Melting point (°C)
0g
0
3.2
50 g
-0.3
2
100 g
-6.3
-4.4
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7. Summarize: How does increasing the concentration of salt affect the freezing and melting
points of water? The greater concentration of slat in water, the larger the freezing
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150 g ra ms of salt a re add ed? H ow ab out reso urce with2 00g rams ofsalt ? Writ e you r p redic tions i n
depression will be, meaning it will take more time and cold
t mperatu es to freeze the ice.
8. Analyze: How much is the freezing point lowered by adding 50 g of salt? It is depressed 6
degrees Celsius.
9. Test: Based on your data, what do you expect the freezing and melting points to be when
the appropriate columns below.
Amount of salt
150 g
Freezing Point
(predicted)
-7.5 Degrees C
Freezing Point
( ctual)
-10
Melting point
(predicted)
-3
Melting Point
(actual)
-3.2
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-9 Degrees C
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<10
200 g
Degrees C
-4 Degrees C
<10 Degrees C
After writing your predictions, use the Gizmo to find the actual values. Fill in as much of the
table as you can. (Write “less than -10 °C “ or “< -10 °C “ if the actual value is less than the
minimum
This
room temper ture available in the
Gizmo.)
10. Think and discuss: Why do people add salt to roads and walkways in the winter?
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Doing so lowers the freezing point of the water that forms ice, this leads to melting
and would prevent falling snow or rain from being able to freeze.
This study source was downloaded by 100000802358847 from CourseHero.com on 06-08-2021 20:20:40 GMT -05:00
2019
https://www.coursehero.com/file/69624229/Freezing-Point-of-Salt-Water-docx/
Activity B:
Get the Gizmo ready:
Transformation
rates
Click Reset.
Turn on the Transformation rate checkbox.
Introduction: The transformation rate is the speed at which particles are changing from one
phase to another. In the Transformation rate display, the purple bar represents the speed of
liquid water changing to ice, while the green bar indicates the speed of ice changing to liquid.
Question: How does salt affect transformation rates?
1. Observe: Move the Room temp. slider back and forth, and observe the effect on
the transformation rates. What do you observe?
When you move the slider to the right of 0 Degrees Celsius, the blue bar rises while
the purple bar drops and vice versa.
2.
Explain: As the temperature of a liquid increases, the average
wasspeedofthe molecomules increases
.
as well. How does this account for the observed changes in transformation rates? Only when water is frozen
and when
resourceitisdefrosting,CourseHerowillthetransformatinate change.
3. Predict: How will adding salt affect the water-to-ice and ice-to-water transformation
rates? The scale would probably be different.
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4. Experiment: Set the Room
temp.to -5.0 °C, and bserve the transformation rates. Add 50
g of salt before the ice reaches the bottom of the funnel.
A. How does adding salt affect each transformation rate? Some particles only freeze
halfway.
B.
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ThisNow addshared50 more grams of salt. What happens now?
Nothing is frozen.
This study source was downloaded by 100000802358847 from CourseHero.com on 06-08-2021 20:20:40 GMT -05:00
2019
https://www.coursehero.com/file/69624229/Freezing-Point-of-Salt-Water-docx/
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