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The Properties of Water Hands-On Labs, Inc. Version 42-0129-00-02

Review the safety materials and wear goggles when working with chemicals. Read the entire exercise before you begin. Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise.

Experiment Summary:

You will explore unique characteristics of water. You will investigate surface tension, cohesion and adhesion, density, specific gravity, and phase changes. You will experiment with capillary action, create a heating curve, and calculate the density and specific gravity for a variety of substances.

EXPERIMENT

Learning Objectives Upon completion of this laboratory, you will be able to:

● Describe and list some of the defining characteristics of water.

● Define adhesion, cohesion, and capillary action.

● Describe melting, vaporization, sublimation, condensation, freezing, and deposition.

● Produce a heating curve of water.

● Prepare a graph and interpret results.

● Calculate density and specific gravity.

Time Allocation: 4.5 hours

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Experiment The Properties of Water

Materials Student Supplied Materials

Quantity Item Description 1 Clear tape 1 Coin (Penny, nickel, dime, or quarter) 1 Crushed ice* 1 Cup or drinking glass, 2 oz.– 8 oz., flat top 1 Distilled water 1 Dish soap 1 Food coloring (blue or green) 1 Isopropyl alcohol (10 mL) 1 Matches 2 Needle or straight pin 1 Olive oil (10 mL)

50-100 Paper clips 1 Roll of paper towels 1 Source of tap water 1 Timer (watch, cell phone, etc)

HOL Supplied Materials

Quantity Item Description 1 Beaker, 100 mL, glass 1 Beaker, 250 mL, glass 1 Burner fuel 1 Burner stand 1 Capillary tubes (3 tubes of varying diameter) 1 Graduated cylinder, 25 mL 1 Digital scale 1 Metric ruler 1 Pair of safety goggles 3 Pipets, empty, short stem 1 Test tube, 25 x 150 mm 1 Thermometer, analog

* The experiment requires crushed ice. Ensure that you have ample time to prepare ice before starting.

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Experiment The Properties of Water

Note: To fully and accurately complete all lab exercises, you will need access to:

1. A computer to upload digital camera images.

2. Basic photo editing software such as Microsoft® Word or PowerPoint®, to add labels, leader lines, or text to digital photos.

3. Subject-specific textbook or appropriate reference resources from lecture content or other suggested resources.

Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit.

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Experiment The Properties of Water

Background Unique Properties of Water

Water is one of the most important substances on Earth, as it is an essential resource for all living things. Approximately 70% of Earth’s surface is covered in water and the human body is composed of approximately 60% water. Water is the only substance that people regularly experience in all three states of matter: solid, liquid, and gas. As water is essential to living organisms, it is critical to gain an understanding of the properties of water and how it facilitates daily life.

Many of the unique properties of water are the result of its polar covalent molecular structure, and ability to form intermolecular hydrogen bonds with other water molecules. Hydrogen bonding is the result of an attraction between molecules that contain a partially positive hydrogen atom (H+) and a highly electronegative atom such as oxygen (O), nitrogen (N), or fluorine (F). Hydrogen bonding is exhibited between water molecules (H2O) in its liquid and solid phases. When multiple water molecules interact, the partially positively charged hydrogen end of one molecule is attracted to the partially negatively charged oxygen end of another molecule. See Figure 1.

Figure 1. Molecular structure of water. A. Polarity of water: a center of negative charge (δ-) near the oxygen atom and centers of positive charge (δ+) near the hydrogen atoms. ©molekuul.be B.

Hydrogen bonding in liquid H2O.

Water, as a liquid, does not exist as separate water molecules, but as a loose network of molecules linked by hydrogen bonds. These hydrogen bonds, while much weaker than the covalent bonds within the water molecule, are responsible for the tendency of water molecules to “stick” together. The term used to describe the tendency of like molecules to “stick” together is cohesion. Water has a high cohesion compared to many other substances. The cohesive nature of water is evident in a water droplet; without cohesion the water would not hold its shape. See Figure 2. When liquids with strong intermolecular hydrogen bonds, such as water, have strong cohesive forces they also exhibit high surface tension. Surface tension is the resistance of the object to increase its surface area. Surface tension creates a “skin” or “shell” around the liquid, strong enough to support light objects. Surface tension is the property that allows small insects to walk on water without breaking through the surface tension (skin) of the liquid.

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Experiment The Properties of Water

Figure 2. Cohesive nature of water. As a result of the intermolecular hydrogen bonding in water, the water prefers to stick together rather than interact with its surrounding surface, creating

surface tension around the water droplet. © koh sze kiat

In addition to cohesive forces, water also exhibits adhesive forces. While cohesive forces are the result of the intermolecular hydrogen bonds within the water, adhesive forces are the result of attractive forces between the water and its container, or surrounding surface. Water molecules have a polar covalent molecular structure; therefore, they have a desire to interact with surfaces containing polar bonds, such as glass. See Figure 3.

Figure 3. Adhesive nature of water. (Left) Water droplet on nonpolar surface, (Right) Water droplet on a polar surface. As the result of the polar water molecule’s desire to interact with the

polar glass surface, the water droplet will spread out along the surface of the glass.

A third property of water results from the interplay of the cohesive and adhesive forces and is called capillary action. Capillary action is the spontaneous upward rising of a liquid through a narrow tube, or opening.

Capillary action is how water and the nutrients that water carries are brought up from the roots to the

leaves in a plant.

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Experiment The Properties of Water

Density and Specific Gravity

Density is defined as mass per unit of measure, which is most often volume. Density is a way to describe how heavy an object is for its size. The density of a liquid is usually reported as grams per milliliter (g/mL), while the density of a solid is usually reported as grams per cubic centimeter (g/cm3). The density of water is accepted at 1 g/mL. Substances with a density greater than 1 g/ mL will sink when placed in water, while objects with a density less than 1 g/mL will float when placed in water. The density of an object is determined with the following equation:

Specific gravity is the ratio of the density of a substance to the density of a reference substance. For liquids, this reference substance is usually water. When calculating the specific gravity, the

densities must be calculated at the same temperature and pressure.

Substances with a specific gravity less than 1 are less dense than water, and thus tend to float when placed in water. Conversely, substances with a specific gravity greater than 1 are denser than water, and thus tend to sink when placed in water.

Phase Changes

Adding energy to, or removing energy from, a substance (such as water) may cause a change in its state of matter. Energy may be added or removed by increasing or decreasing temperature. When energy is added to a solid or a liquid substance, the molecules move more quickly, and may eventually break the weak intermolecular forces that hold them together. Breaking these intermolecular forces can result in a change in the state of matter. On the other hand, when energy is removed from a liquid or a gas substance, the molecules move more slowly and eventually form intermolecular bonds. Because intermolecular forces are different for each substance, temperatures in which a phase change occurs differ for each substance, and become unique properties of those substances.

As shown in Figure 4, changes among states of matter may fit into six categories. Energy is required to overcome molecular attraction. Changes in states of matter moving from a solid to liquid phase (melting), a liquid to gas phase (vaporization), or a solid to gas phase (sublimation), require energy. When moving in the opposite direction, from a gas to liquid phase (condensation), a liquid to solid phase (freezing), or a gas to solid phase (deposition), energy is released. Notice that during the processes sublimation and deposition, the phase change is between the solid and gas state, and the particles do not enter an intermediary liquid phase.

MassDensity = Volume

(substance)

(H O)

densitySpecific Gravity = density

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Experiment The Properties of Water

Figure 4. Changes among the phases of matter. Red arrows represent phase changes that require energy (heat) and blue arrows represent phase changes that release energy (cooling).

Heating Curve

A heating curve, as shown in Figure 5, is a graph that plots the temperature of a substance over time as heat is applied to the substance. The heating curve describes temperature changes over states of matter, and can be used to determine the melting point and boiling point of substances. There is no increase in the temperature of the substance at the melting point during the melting process or at the boiling point during the boiling process because all of the energy applied to the substance is used to weaken intermolecular forces until they are all broken.

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Experiment The Properties of Water

Figure 5. Model heating curve. Melting and boiling points occur when temperature does not increase.

Pressure may also affect the state of matter. When increasing pressure, molecules move more quickly and bump into each other more often. This increases the temperature of the solution and also causes more of the molecules to get excited. This increases the number of intermolecular bonds that are broken. Therefore, with more pressure, substances are more likely to vaporize, or sublime. When pressure is decreased, molecules are less likely to bump into each other, and fewer intermolecular bonds are broken. Substances are more likely to condense or undergo deposition with less pressure. However, pressure has very little effect on the liquid/solid transition. This emphasizes the fact that liquids and solids are already in a condensed state and are considered incompressible. Therefore, increasing pressure does not increase the frequency of liquid and solid molecules bumping into each other and does little to raise the melting point.

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Experiment The Properties of Water

Exercise 1: Water and its Unique Properties In this exercise, you will investigate the properties of cohesion and adhesion in water. You will demonstrate how these properties work together to create surface tension and capillary action.

Part I

1. Fill the 100-mL glass beaker with tap water so that the beaker is almost full.

2. Hold a needle vertically, as close to the water in the beaker as possible without actually touching the needle to the water.

Note: vertically is up and down in direction, imagine the post of a stop sign.

3. Gently drop the needle onto the water.

4. Record the observations in Data Table 1 of your Lab Report Assistant in the “Vertical” Column.

5. Carefully retrieve the needle from the water and dry it.

Note: The needle must be completely dry between each step. If you would like to repeat any steps, make sure to dry the needle before you begin.

6. Hold the needle horizontally, as close to the water in the beaker as possible without actually touching the water.

7. Gently place the needle onto the water.

Note: Do not drop the needle at an angle.

8. Record the observations in the “Horizontal” column of Data Table 1.

9. Drain the water from the beaker and dry both the beaker and needle.

Part II

1. Place a paper towel on a flat surface.

2. Place the 2 oz.– 8 oz. cup or drinking glass on the paper towel.

3. Fill the cup or drinking glass just above the brim with tap water without allowing the water to overflow. See Figure 6.

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Experiment The Properties of Water

Figure 6. Water filled just above brim.

4. Estimate how many paper clips you think can be added to the cup before the water overflows, breaking the surface tension. Record the estimation in Data Table 2 of your Lab Report Assistant.

5. Add paper clips to the cup 1 at a time while counting the number added. The paper clips will sink to the bottom of the cup. Add paper clips until the surface tension breaks and water spills over the cup.

6. Record the results in Data Table 2.

7. Drain the water from the cup or glass and then dry both the cup or glass and paper clips.

Part III

1. Place a paper towel on a flat surface.

2. Place a coin of any type on the paper towel. Ensure that the coin is level.

3. Fill a pipet with tap water.

4. Make a guess as to how many drops of water you think can be placed on the coin before the surface tension of the water will break and the water will flow off the face of the coin. Record your hypothesis in Data Table 3 of your Lab Report Assistant.

5. Using the pipet, place 1 drop of water at a time onto the coin until the water flows over the face of the coin, see Figure 7. Count the drops as they are added and record the final number of drops in Data Table 3.

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Experiment The Properties of Water

Figure 7. Dropping water onto a coin and proper hand placement.

6. Dry the coin and remove the water from the pipet. Keep the pipet for use in the Exercise 3.

Questions A. How did the experiment in Part I demonstrate surface tension? Use your experiment

observations when answering this question.

B. In Part I, when adding the needle to the water, which approach worked best to balance the needle on the water — the vertical or horizontal placement? Explain your answer.

C. In Part II, how did your paper clip estimation compare to your paper clip results?

D. In Part III, how were the properties of adhesion and cohesion demonstrated in the experiment?

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Experiment The Properties of Water

Exercise 2: Capillary Action In this exercise, you will further investigate the properties of cohesion and adhesion in water. You will determine how the internal diameter of a capillary tube affects the rate the water travels up the height of the tube.

1. Remove the small cardboard piece that contains the 3 capillary tubes of varying internal diameters. The internal diameters of the capillary tubes are 0.25 mm, 0.58 mm, and 1.0 mm. Think about adhesion and cohesion and develop a hypothesis as to which capillary tube would be the first to draw water through the height of the tube. Which tube would be the last to draw water though the height of the tube? Record your hypothesis in Data Table 4 of your Lab Report Assistant.

2. Carefully remove the 3 capillary tubes from the cardboard piece. See Figure 8.

Figure 8. Capillary tubes on cardboard piece.

3. Invert the 25 x 150 mm test tube so that it is able to stand on a table.

4. Use tape to carefully affix each of the capillary tubes to the outside of the 25 x 150 mm test tube. Ensure that the bottom of the capillary tubes are evenly aligned, 2–5 mm above the bottom of the test tube, see Figure 9. It is important that the tape is placed near the center of the capillary tubes and not blocking the openings at the top and bottom of the tubes.

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Experiment The Properties of Water

Figure 9. Capillary tubes affixed to the outside of the 25 x 150 mm test tube. The bottoms of the tubes are evenly aligned. Note that the opening of the test tube is flush against the table.

5. Fill the 100-mL glass beaker with approximately ½ inch of tap water.

6. Add 2–3 drops of blue or green food coloring to the water and swirl the beaker to mix the solution.

7. Start the timer and immediately place the test tube into the beaker with the colored water. See Figure 10. The water will immediately begin to travel up the capillary tubes. Allow the capillary tubes to remain in the colored water for 30 minutes. Do not disturb or bump the setup during the 30 minutes.

Figure 10. Capillary tubes in colored water.

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Experiment The Properties of Water

8. At the end of the 30 minutes, use the ruler to measure the distance (cm) the water traveled in each capillary tube. Record the data in Data Table 5 of your Lab Report Assistant.

9. Create a line graph of the relationship between the internal diameter of the capillary tube and the distance water traveled. Plot the internal diameter on the independent axis (x-axis), and plot the distance traveled on the dependent axis (y-axis).

10. Resize the graph and insert it into Data Table 6 of your Lab Report Assistant. Refer to the appendix entitled, “Resizing an Image” for guidance with resizing an image.

11. Wash and dry the beaker. Return all items to the kit for future use.

Questions A. How did this activity demonstrate capillary action? Explain your answer using your experiment

results and observations.

B. Did your experimental results support or refute your hypothesis? Use the data collected in Data Table 5 to support your answer.

C. Describe the relationship between the internal diameter and the distance the water traveled. Was there any correlation between the two? Use the graph created in Data Table 6 to support your answer.

D. How would you expect your results to change if the capillary tubes were made of plastic instead of glass?

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Experiment The Properties of Water

Exercise 3: Density and Specific Gravity In this experiment, you will determine the density of water, olive oil, and isopropyl alcohol. You will then calculate the specific gravity of each liquid.

1. Gather the graduated cylinder, distilled water, short stem pipets, isopropyl alcohol, and olive oil.

2. Place the clean, dry, 25-mL graduated cylinder on the tared scale. Record the mass of the graduated cylinder (g), in Data Table 7 of your Lab Report Assistant under “Mass A” column for water.

3. Fill the graduated cylinder with 5.0 mL of distilled water; use the short stem pipet to help measure exactly 5.0 mL of water. Record the volume in Data Table 7.

4. Place the 25-mL graduated cylinder with 5.0 mL distilled water on the tared scale. Record the mass of the graduated cylinder + liquid (g) in Data Table 7 under “Mass B”.

5. Calculate the mass of the water by subtracting “Mass A” from “Mass B.” Record the mass of the water in Data Table 7.

6. Pour the water down the drain and fully dry the graduated cylinder.

7. Repeat steps 2–6 for the isopropyl alcohol and olive oil.

8. Calculate the densities of the water, isopropyl alcohol, and olive oil. Record the density of each liquid in Data Table 7.

9. Calculate the specific gravity for each of the 3 liquids and record in Data Table 7.

10. Wash and dry all items and return them to the kit for future use.

Questions A. If the three substances tested in this exercise were poured into the same graduated cylinder,

in what order would you expect them to layer? Use your data in Data Table 7 to support your answer.

B. Ice floats in water. Use your experience with density and specific gravity in this exercise to explain how ice is able to float in water. What happens to water as it freezes that allows it to float in water?

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Experiment The Properties of Water

Exercise 4: Temperature and Phase Changes In this exercise, you will make observations of the phase changes of water (H2O). You will measure temperature and create a heating curve to determine the melting point and boiling point of water.

1. Gather the 250-mL beaker, approximately 150 mL of crushed ice, a watch or timer, the thermometer, burner stand, burner fuel, and matches.

Note: Large ice cubes may be crushed by placing them in a large plastic bag, placing the bag on a durable surface, and breaking the pieces apart with a hammer or other heavy object.

2. Fill the beaker to about the 150-mL line with crushed ice.

3. Place the thermometer in the center of the ice. Do not allow the thermometer to touch the sides or bottom of the beaker.

4. After holding the thermometer in the ice for about a minute, note the time and record temperature at 0 minutes in Data Table 8 of your Lab Report Assistant. Additionally, record your observations about the state of matter (solid, liquid, or gas) of the water in Data Table 8.

5. Uncap the burner fuel, light the wick with a match or lighter, and place the fuel under the stand on a pie pan as shown in Figure 11.

Figure 11. Burner setup. Note that the flame is blue which is sometimes difficult to see.

6. Place the beaker on the burner stand. Keep holding the thermometer in the middle of the ice.

7. Start the timer and begin taking temperature and observation readings every minute, recording your findings in Data Table 8.

Note: It is important that you record both the temperature AND the state or states of matter present every minute throughout the experiment.

8. Gently stir the ice with the thermometer as it heats.

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Experiment The Properties of Water

9. Continue to stir the ice or water and record temperature and observations every minute until the water has boiled for 5 minutes. Do not allow the thermometer to rest on the glass of the beaker.

10. Extinguish the burner fuel by lightly placing its cap over the flame; do not tighten cap until the burner fuel container has fully cooled.

11. Thoroughly wash and rinse the equipment for future use.

12. Using the temperature data recorded in Data Table 8, create a heating curve.

● Plot time (minutes) on the x-axis (horizontal axis) and temperature (°C) on the y-axis (vertical axis). Connect the plotted points with a line.

● Label the heating curve to show each phase of matter (solid, solid + liquid, liquid, liquid + gas).

● Label the melting point and boiling point on the heating curve.

● Resize the graph and insert it into Data Table 9 of your Lab Report Assistant.

Note: An example heating curve is given in Figure 5 of the Background.

13. When you are finished uploading photos and data into your Lab Report Assistant, save your file correctly and zip the file so you can send it to your instructor as a smaller file. Refer to the appendix entitled “Saving Correctly” and the appendix entitled “Zipping Files” for guidance with saving the Lab Report Assistant correctly and zipping the file.

Questions A. Are there parts of the curve with positive slopes and parts that are flat (slope of zero)? What

states of matter are present when the slope of the heating curve is positive and what states of matter are present when the slope is zero or close to zero?

B. Describe the key characteristics for the three states of matter.

C. Define the melting point. What was the observed melting point of water?

D. Define boiling point. What was the observed boiling point of water?

E. What happens to heat energy when it is not increasing the temperature of the substance in the beaker? Use your heating curve to explain your answer.

F. Was temperature perfectly constant during your test while the water was melting and while it was boiling? Explain why or why not.

G. The published melting point of H2O is 0°C, and the published boiling point is 100°C. Why may you have found different values?

H. Use the following information to determine if the intermolecular forces of isopropyl alcohol are greater or weaker than the intermolecular forces of water. Explain your answer. The melting point of isopropyl alcohol (rubbing alcohol, C3H8O) is about -90°C and the boiling point is about 82°C.

Experiment The Properties of Water

The Properties of Water Hands-On Labs, Inc. Version 42-0129-00-02

Lab Report Assistant This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 1: Water and its Unique Properties Data Table 1. Needle Observations.

Vertical Observations Horizontal Observations

Data Table 2. Paper Clips Needed to Break Surface Tension.

Estimation Result

_____ Paper clips _____ Paper clips

Experiment The Properties of Water

Data Table 3. Drops of Water.

Estimation Result

Questions A. How did the experiment in Part I demonstrate surface tension? Use your experiment

observations when answering this question.

B. In Part I, when adding the needle to the water, which approach worked best to balance the needle on the water — the vertical or horizontal placement? Explain your answer.

C. In Part II, how did your paper clip estimation compare to your paper clip results?

_____ Drops of water _____ Drops of water

Experiment The Properties of Water

D. In Part III, how were the properties of adhesion and cohesion demonstrated in the experiment?

Experiment The Properties of Water

Exercise 2: Capillary Action Data Table 4. Capillary Tube Hypothesis.

Hypothesis

Data Table 5. Distance Traveled.

Capillary Tube Distance (cm) 0.25 mm

0.58 mm

1.0 mm

Data Table 6. Internal Diameter versus Distance Traveled.

Graph

Experiment The Properties of Water

Questions A. How did this activity demonstrate capillary action? Explain your answer using your experiment

results and observations.

B. Did your experimental results support or refute your hypothesis? Use the data collected in Data Table 5 to support your answer.

D. How would you expect your results to change if the capillary tubes were made of plastic instead of glass?

Experiment The Properties of Water

Exercise 3: Density and Specific Gravity Data Table 7. Density and Specific Gravity.

Mass A Mass B Mass B - A

Liquid Volume (mL) Graduated

Cylinder (g)

Graduated

Cylinder with liquid (g)

Liquid (g) Density

g/mL Specific Gravity

Water

Isopropyl alcohol

Olive oil

Questions A. If the three substances tested in this exercise were poured into the same graduated cylinder,

in what order would you expect them to layer? Use your data in Data Table 7 to support your answer.

Experiment The Properties of Water

Exercise 4: Temperature and Phase Changes Data Table 8. Temperature and Observations for Heating Curve.

Time (Min) Temperature (°C) Observations 0 1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Experiment The Properties of Water

Data Table 9. Internal Diameter versus Distance Traveled.

Graph

Questions A. Are there parts of the curve with positive slopes and parts that are flat (slope of zero)? What

states of matter are present when the slope of the heating curve is positive and what states of matter are present when the slope is zero or close to zero?

B. Describe the key characteristics for the three states of matter.

C. Define the melting point. What was the observed melting point of water?

D. Define boiling point. What was the observed boiling point of water?

Experiment The Properties of Water

E. What happens to heat energy when it is not increasing the temperature of the substance in the beaker? Use your heating curve to explain your answer.

F. Was temperature perfectly constant during your test while the water was melting and while it was boiling? Explain why or why not.

G. The published melting point of H2O is 0°C, and the published boiling point is 100°C. Why may you have found different values?

Experiment The Properties of Water