the freezing point · 2020. 5. 6. · liquids, gases, and solids can all dissolve into a...
TRANSCRIPT
The Freezing Point
Olivia Nickerson
October 9, 2019
Physical science
Abstract
Water affects our daily lives greatly. The purpose of this experiment was to see how
different chemicals can affect the freezing point of water. It was hypothesized that adding salt to
water would lower the water’s freezing point and that it would lower it more than adding sugar
would. The results definitely showed that both salt and sugar can lower water’s freezing point,
and suggested that salt lowers the freezing point more than sugar does. While pure water froze at
4.7℃, the salt and water mixtures froze at the temperatures 1℃, 0℃, and -2.7℃. the sugar and
water mixtures froze at the temperatures 4.3℃, 1℃, and -1.3℃. Knowing how different
chemicals affect water’s freezing point can help to understand the world, which is filled with
water, works.
Table of Contents
1.0 Question
2.0 Purpose
3.0 Variables
3.1 Independent Variables
3.2 Dependent Variables
3.3 Controlled Variables
4.0 Hypothesis
5.0 Background Research
6.0 Results
7.0 Data Analysis
8.0 Concentration
9.0 Conclusion
10.0 Acknowledgements
11.0 Reference List
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1.0 Question
Do different chemicals effect the freezing point of water?
2.0 Purpose
The purpose of this experiment is to determine whether salt and sugar affect the freezing point of
water.
3.0 Variables
3.1 Independent variables
Salt and sugar.
3.2 Dependent variables
The freezing point of the water.
3.3 controlled
The amount of water, type of container, the amount of salt, the amount of sugar, time given to
freeze, brand of salt, brand of sugar.
4.0 Hypothesis
If salt is added to water, then freezing point will decrease more than if sugar is added to water.
5.0 Background research
Who does not love ice cream? Everyone loves this frozen, sweet treat, but why does it stay
frozen? In the same way ice also freezes. There are ways to keep water frozen at room
temperature or to even keep it from freezing. It is possible to change the freezing point of water
by applying pressure, adding additives, supercooling it, or turning it into a solution. There are
multiple ways for water to stay in liquid form when it is under zero degrees Celsius. Do different
chemicals change the freezing point of water? Knowing how to change the freezing point of
water and understanding what solutions, mixtures, and compounds are key to performing an
experiment that answers this very question. Changing the freezing point of liquids is used in our
everyday lives like when they put salt on the roads or to make ice cream.
The freezing point of water can be changed by multiple techniques. A material being liquid,
solid, or gas depends both on its pressure and its temperature (Baird, 2013). With most liquids if
pressure is applied the temperature that the liquid freezes is raised (Baird, 2013). Molecules ae
forced closer together when pressure is applied (Baird, 2013). Water is unique because applying
pressure actually causes the freezing point to lower. This is because when water molecules bond
to form ice they spread out (Baird, 2013). The spreading out is what gives ice the ability to float
(Baird, 2013). Water in its liquid form is more dense than ice (Baird, 2013). With enough
pressure it is possible for water to be liquid water under zero degrees Celsius (Baird, 2013).
Under standard pressure it is possible for water to be supercooled to as cold as -40 degrees
Celsius (Baird, 2013). If water is really still and very pure without anything to crystallize on,
then the water will remain liquid well under zero degrees Celsius. This water is called
supercooled (Baird, 2013). Supercooled water does not freeze only because the lack of any
nucleation centers (Baird, 2013). Nucleation centers are what water uses to start freezing. They
can be something like dust or even a vibration. Impurities can also be nucleation centers (Baird,
2013). If a nucleation center is provided for supercooled water, the water rapidly freezes (Baird,
2013). One example of natural supercooled water is freezing rain, which once it hits something
the raindrop freezes since it has now gained a nucleation center (Baird, 2013). Freezing rain,
since it is just supercooled water, turns to ice as soon as it gains a nucleation center (Baird,
2013). Another way to change water’s freezing point is to turn it into a solution. Solutions are a
mixture which homogenous throughout (Solutions, 2005). Solutions can be found everywhere
around us (Chemistry, 2018). The solvent of a solution is whichever component has the largest
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amount in the solution (Solutions, 2005). The solute of the solution is the component in the
solution in a lesser amount (Solutions, 2005). If both components make up 50% of the solution
either can be called the solute (Chemistry, 2018). Additives can cause water to stay liquid under
zero degrees Celsius (Baird, 2013). There are different ways to change water’s freezing point,
but the experiment involves turning water into a solution.
Solutions are everywhere around us. They are in our bodies and the air surrounding us
(Chemistry, 2018). Saltwater is a solution. In saltwater water is the solvent (Solutions, 2005).
Saltwater and pure water look the same, but the two taste different. Even with a microscope you
cannot see the salt in saltwater when it has been fully dissolved (Solutions, 2005). Saltwater and
pure water have different qualities. Saltwater’s boiling point is higher than that of pure water
(Solutions, 2005). Salt lowers the freezing point of water (Baird, 2013). Saltwater conducts
electricity (Solutions, 2005). Water molecules stick to salt ions more than each other when salt is
dissolved into water (Baird, 2013). When water and salt form a solution the salt separates into
ions (Solutions, 2005). If enough salt was added, water could stay liquid at -21 degrees Celsius
(Baird, 2013). Salt is also used in order to change ice into its liquid form. Solutions can be at any
phase (Chemistry, 2018). The three solutions: liquid, gaseous, and solid are named by the state
the solution is in (Chemistry, 2018). Aqueous solutions are solutions that water acts as the
solvent in (Solutions, 2005). Saltwater is an example of an aqueous solution (Solutions, 2005).
Non-aqueous solutions are solutions that water does not act as the solvent in (Solutions, 2005). A
gaseous mixture is a solution in a gas state (Chemistry, 2018). Gaseous mixtures usually are
homogeneous (Chemistry, 2018). Most gaseous mixtures are gas-gas solutions (Chemistry,
2018). Solid solutions are solutions that have a solid for the solvent (Solutions, 2005). Alloys are
solid solutions (Chemistry, 2018). Brass is an example of a solid solution (Solutions, 2005).
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Liquids, gases, and solids can all dissolve into a liquid-form solvent and create a liquid solution
(Chemistry, 2018). Solubility is “the maximum amount of a substance that can be dissolved in a
given volume of a solvent” (Chemistry, 2018, Section 7.3). Saturated solutions have the
maximum amount of solute dissolved in them (Chemistry, 2018). Saturated solutions are
solutions that have reached their max solubility (Chemistry, 2018). Any solute added to a
saturated solution will not dissolve (Chemistry, 2018). Unsaturated solutions are solutions that
have yet to reach their maximum solubility (Chemistry, 2018). Most solutions actually are
unsaturated (Chemistry, 2018). Soluble solutes “dissolve in a particular solvent” (Chemistry,
2018, Section 7.11). Insoluble solutes “do not dissolve in a particular solvent” (Chemistry, 2018,
Section 7.11). Solutions are extremely useful, but what is a solution?
Solutions are a type of mixture. When talking about solutions, mixtures, and compounds it is
necessary to understand chemical formulas and concentrations as well. The “concentration of a
solution describes the quantity of a solute that is contained in a particular quantity of that
solution” (Chemistry, 2018, Section 7.7). There are multiple ways to express concentrations
(Chemistry, 2018). “Mass/mass percent, volume/volume percent, and mass/volume percent
indicate the percentage of the overall solution that is solute. Parts per million (ppm) and parts per
billion (ppb) are used to describe very small concentrations of a solute.” (Chemistry, 2018,
section 7.11). Mixtures and compounds are two different things. Compounds are unable to be
separated because of physical techniques (Solutions, 2005). A compound’s composition is
always the same (Solutions, 2005). Compounds are substances with more than one different
element that have their atoms within a definite ratio (Solutions, 2005). Usually the compound’s
properties are distinct from that of the elements composing it (Solutions, 2005). The elements
inside a compound do not just mix together but are bonded to each other in a certain way
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(Solutions, 2005). However, inside a mixture components keep their chemical properties
(Solutions, 2005). Mixtures’ compositions are variable, and the properties relate to its
components (Solutions, 2005). Mixtures are matter which contains multiple pure substances that
are able to be separated by physical techniques (Solutions, 2005). There are two kinds of
mixtures: homogeneous and heterogeneous (Chemistry, 2018). Heterogeneous mixtures have
different looking regions of the same mixture and are non-uniform (Chemistry, 2018).
Homogeneous mixtures are so intimately combined they are mistakenly observed as if they were
a single substance (Chemistry, 2018). Being homogeneous throughout means the ions or
molecules involved are very well mixed so the mixture’s composition throughout is uniform
(Solutions, 2005). Knowing what mixtures are and knowing how to show concentrations are key
to setting up an experiment.
The purpose of this experiment is to find out whether different chemicals affect the freezing
point of water. Understanding the different ways to change the freezing point of water and what
solutions and mixtures are crucial for both designing and performing an experiment to answer
that question. The hypothesis for this experiment is if salt is added to water then the freezing
point will lower making an edible solution. Using what is known about solutions, compounds,
mixtures, and changing the freezing point of water, as well as the results of the experiment,
changing the freezing point of liquids can be applied to real life situations.
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6.0 procedure
The equipment and materials used in this experiment were as follows:
• water
• Ice
• Permanent marker
• Table salt (500g)
• Granulated sugar (360g)
• Small spoon
• Test tubes, 16 mm by 15 mm (7)
• Test tube rack
• 250 mL beakers (6)
• 100 mL graduated cylinder
• Gram balance
• Thermometer
• Stir rods (2)
• Large Styrofoam cup
1. Filled Styrofoam cup ¾ full with ice and covered the ice with ¼ - ½ inches of table salt
2. Stirred the ice-salt mixture with spoon
3. Checked temperature of ice-salt mixture with thermometer
4. Rinsed the thermometer off
5. Using permanent marker, labeled one test tube and one beaker #1
6. Prepared the beaker labeled #1. Used scale to weigh 2.9g of table salt into the beaker.
Measured 100 mL of water in graduated cylinder, and poured it into the beaker with salt.
Stirred until all the crystals were dissolved.
7. Rinsed the stirring rod
8. Filled test tube #1 one-third full with test liquid #1. Placed test tube in Styrofoam cup
with ice and salt making sure that liquid is below the ice and salt.
9. Stirred the test liquid gently with the thermometer while keeping track of temperature.
10. Checked temperature frequently
11. Once ice crystals started appearing, recorded temperature
12. Melted the ice and disposed of the liquid.
13. Repeated steps 6-12 two more times (making more ice-salt mixture in the Styrofoam cup
when needed)
14. Prepared the other test tubes. Repeating step 5-12 with each type of test liquid
Test liquid #2= 5.8g salt in 100 mL water
Test liquid #3= 11.7g salt in 100mL water
Test liquid #4= 17.1g sucrose in 100mL water
Test liquid #5= 34.2g sucrose in 100mL water
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Test liquid #6= 68.5g sucrose in 100mL water
Test liquid #7= 100mL water
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6.1 Photographs of Procedure
Figure 1. The Seven Test Tubes on the Test Tube Rack
Figure 2. Filling Graduated Cylinder with 100 mL of Water
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Figure 3. Preparing Test Tube for Ice Bath
Figure 4. Partially Frozen Mixture
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Figure 5. Scale Used to Weigh Salt and Sugar
7.0 Results
Table 1. Measurements Necessary for Calculating the Molality
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Table 2. Expected Freezing Point Depression
Figure 6. Molality and Freezing Point Depression
mixture mixture
Molality
Freezing point
depression
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8.0 Data Analysis
Mixture #1 froze at 1℃. Mixture #2 froze at 0℃. Mixture #3 froze at -2.7℃. Mixture #4
froze at 4.3℃. Mixture #5 froze at 1℃. Mixture #6 froze at -1.3℃. The control, which was
pure water, froze at 4.7℃. Since 0℃ is the freezing point of water it is relatively safe to
assume that the temperatures measured were all off by 4.7℃. This would explain why
multiple mixtures froze above the freezing point of water (0℃). All of the mixtures froze
under the temperature that the control froze at. Based on the results, when water has salt or
sugar added the freezing point will be lower than pure water regardless of whether it was salt
or sugar added. The results of this experiment show that the water with salt froze at lower
temperatures than the water with sugar. The hypothesis of this experiment was that the water
mixed with water would freeze at lower temperatures than that of the water mixed with
sugar. The results showed that both saltwater mixtures and sugar-water mixtures have a
lower freezing point than pure water. However, the saltwater froze at lower temperatures.
The results were conclusive in regard to whether different chemicals effect the freezing point
of water.
An observation was made that even though two of the mixtures had the same molality
(mixtures #3 and #6, both 2 mol/kg) they had different freezing point depressions.
It was noted that the sugar-water mixtures in some cases froze less completely, although the
experiment was concerned with at what temperature ice crystals started forming not with
whether certain mixtures froze more completely than others.
8.0 Conclusion
The purpose of this experiment was to determine whether different chemicals effect water’s
freezing point and if different chemicals change it more than others. The results confirmed
the hypothesis that salt added to water would lower the freezing point and that it would be
lower than the freezing point of water with sugar added. It also showed that sugar lowers
water’s freezing point as well, but not as much as salt does. This experiment was successful
in showing that chemicals do effect water’s freezing point and that the chemicals can affect
water differently than one another. As was stated earlier the thermostat seemed to be off by
4.7℃ so the results are off as well. Practical use of the fact that salt lowers water’s freezing
point are seen when salt is used on roads before snow.
10.0 Acknowledgements
A special thanks is given to my best friend Sophie, her dad, and Cora, her older sister, for
answering all the questions I had even over text. Also, to my brother Nathaniel because he
helped me as I started the experiment.
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11.0 Reference List
Baird, C. (2013, December 9). “Can water stay liquid Below zero degrees Celsius?” Retrieved
November 10, 2019, from https://wtamu.edu/~cbaird/sq/2013/12/09/can-water-stay-liquid-
below-zero-degrees-celsius/.
Washington University in St. Louis. (2005). Solutions. Retrieved November 10, 2019, from
http://www.chemistry.wustl.edu/~coursedev/onlinetutorials/solutions.html.
Western Oregon University. (2018, August 17). Chemistry. Retrieved November 10, 2019, from
http://wou.edu/chemistry/courses/online-chemistry-textbooks/3890-2/ch104-chapter-7-solutions/.
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