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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