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North Star Academy College Preparatory High School

Name: ______________________________

Team_____________________

EDUCATION IS FREEDOM! Date__________/Mr. McIntire

Honors Biology Water Lab

The Properties of Water in Action


Introduction

Water – a substance that is often taken for granted but has remarkable properties that are essential for life. Water and life are so tied together that biologists find it almost impossible to imagine life without water. Unlike other planets in our solar system, the surface of the Earth is covered with liquid water. In fact, the presence of water is one of the main reasons that Earth is habitable. But, what is it about water that makes it so essential for life? As with so many other things in biology, the function of water is a consequence of its structure. Taking a minute to understand the structure of water will make it much easier for you to understand why water acts in so many special ways.

One of the first chemical formulas that you ever learned was most likely H2O, the formula for water. H2O is a shorthand method of representing that each water molecule is composed of two atoms of hydrogen and one atom of oxygen. One molecule of water has two covalent bonds that join each hydrogen atom to the oxygen atom. Remember that a covalent bond consists of a pair of shared electrons. An oxygen atom has a greater electron affinity, or electronegativity, meaning that it has a greater attraction for electrons than a hydrogen atom does. Therefore, when a hydrogen atom and an oxygen atom share a pair of electrons in a chemical bond, the electrons spend more time around the oxygen nucleus than they do around the hydrogen nucleus. This seems like such a trivial point but it has big consequences. The unequal sharing of electrons creates two separate areas of electrical charge. Around the oxygen atom the molecule is partially negatively charged with more electrons, more of the time. Around the hydrogen atoms the molecule is partially positively charged because the electrons spend less time there. This type of bond is called a polar covalent bond thus making water a polar molecule—a molecule with two “poles”—one slightly negative and the other slightly positive. In nature, opposite charges attract. So the positive pole of one water molecule is attracted to the negative pole of another molecule of water. In liquid or solid water, the water molecules arrange themselves to take advantage of this attraction between opposite charges. This attraction has a name: hydrogen bonds. Hydrogen bonds tend to make water sticky, sticking to each other and to other molecules. It is this “stickiness” that underlies the versatile properties of water. Figure 1 below shows three molecules of water, including their partial charges and the hydrogen bonds formed between adjacent water molecules

Figure 1: The polarity and hydrogen bonding of water.

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Now that we understand the basic structure of water, we can examine its four special properties that make it unique. We call these “emergent” properties because they represent properties of the molecule that each of its constituent atoms did not demonstrate on their own. These emergent properties include:

1. Cohesion and adhesion

2. High specific heat

3. Expansion upon freezing (ice floats)

4. Water is a great solvent

5. Water dissociates

Your lab this week will consist of a series of seven activities that deal with some of the properties of water. You will be required to relate each of these activities and natural phenomena back to the sticky structure of water that was just described. These activities can either be seen as “discoveries” as you observe some of the properties of water for yourself, or as culminating activities at the end of the topic to tie these concepts together. This will depend on the day of your lab period. Additionally, each of these activities are short and will be completed during the lab section. While you may not complete all seven activities during the lab, all seven are fair game on your pre-lab quiz.

Objectives

1. Write scientific hypotheses using the VCR method.

2. Explain the observations of natural phenomena using the emergent properties of water.

Materials

Water Dish detergent Toothpicks Water maze Pennies Eyedroppers Celery

Paper towel (3 brands) pre-cut into strips Paper towel 2”x2” squares Food coloring Cooking oil Paperclips Paper Ethanol

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Station 1:Amazing Water Race

Introduction:

Wax is a hydrophobic solid (at room temperature) that excludes water due to differences in solubility. Wax paper, also known as paraffin paper, is a paper that is made moisture proof by the application of wax. The practice of oiling parchment or paper in order to make it moisture-proof dates back to medieval times, when paper impregnated or coated with purified beeswax was widely used to retain or exclude moisture.

Dish soap is a salt of a fatty acids that when used for cleaning, serves as a surfactant in conjunction with water. The water-fearing portion of a fatty acid is made up of the long hydrocarbon fatty acid tail that causes oil and water not to mix; the addition of soap disrupts the hydrogen bonds of water and allows oils to disperse in water and be rinsed away.

In this activity, you will investigate how the properties of water allow it to be used for a “race” across a wax paper surface, and how the addition of dish soap affects your time.

Procedure:

1. Given the following research question, “How does the presence of dilute dish soap affect the surface tension of water?”, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below.

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2. Take “Amazing Water Maze” and with wax paper taped on top and add one drop of water to the “Start” location.

3. Move the maze using your hands to move the water droplet into the “Finish” point. Record the time required to complete the maze in Table 1. Complete THREE trials in the time provided

4. If your water droplet leaves the outside edge of the maze, then you are disqualified and you must begin again. In this case, record your time as an “X”. Be sure to dry off the board before you repeat and try again.

5. Complete steps 2-4 again after dipping a toothpick into the liquid soap and then touching your water droplet with it. Observe the effect of liquid soap as you try to move your water droplet to the “Finish” point of your maze. Record the time required to complete the maze with dish soap in Table 1.

6. Calculate the average number of drops of water and alcohol added to the penny.

Table 1: Time to complete the amazing penny race.

Trial Water Time (sec) Water + Soap Time (sec)123

Avg.

Analysis Questions

1. What emergent property of water (or properties) is being evaluated with this experiment? Explain.

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2. Explain why you received the results that you observed? Why you were able to move the water droplet to the end of the maze without difficulty but the addition of soap made your ability to complete this challenge difficult?

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Station 2:The Penny Trick

Introduction:

The surface tension of a liquid or a mixture is a physical property that is of great importance in biochemistry, as well as common chemistry laboratory techniques that you may be familiar with from 10th grade (distillation, extraction and absorption).

An experiment performed by Vazquez, Alvarez and Navarez measured the surface tension of various aqueous solutions over a range of temperatures (1995)1. These chemists found that the surface tension of these solutions decreased when compared to water alone.

With this information in mind, develop your hypothesis and then complete the penny trick activity below.

Procedure:

1. Given the following research question, How does the presence of dilute alcohol affect the surface tension of water?, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below.

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2. Place two pennies on a flat surface on top of a dry paper towel.

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3. Use the eye dropper provided to add as many drops of water to the surface of a penny without it spilling off the penny. Record the number of drops added on the penny surface before spill-over in Table 2.

4. Use the eye dropper provided to add as many drops of ethanol to the surface of a penny without it spilling off the penny. Record the number of drops added on the penny surface before spill-over in Table 2.

5. Complete at least THREE trials for both steps 3 and 4 in the time provided.

6. Calculate the average number of drops of water and alcohol added to the penny.

7. Clean up your station by drying off the pennies, placing the droppers back into the beaker, and wiping off the counter top.

Table 2: Number of drops on the penny surface before spill-over.

Trial Water Ethanol123

Avg.

Analysis Questions:


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2. Why were many trials taken and averaged?

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3. Identify the independent variable in this experiment.

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4. Identify the dependent variable in this experiment.

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5. Explain why you received the results that you observed? Explain how the polarity of water and its ability to form hydrogen bonds caused this result.

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Station 3:Emulsification of Oils

Introduction:

One of the most important characteristics of fats and lipids, in general, is their insolubility in water due to their non-polar (having no charge) nature. Lipids are made of long chains of hydrocarbons with relatively little oxygen atoms. As a result, they tend to be non-polar and therefore do not dissolve in polar substances such as water. (“Like dissolves like.”) Polar substances can be dissolved in polar substances and non-polar substances can be dissolved in non-polar substances.

In human digestion, lipids are, in part, broken down by bile, which is produced by the liver and aids in the digestion of fats in the small intestine. Bile is not an enzyme, but it does help the enzymes do their job. Bile helps create minute, microscopic fat globules (a process called emulsification). Emulsification is important because it allows lipases (important digestive enzymes that break down fats) to attack and break down the smaller fat globules. Larger fat globs would mean that the lipases could not access the fats (lipids) on the interior of the lipid globs.

In this activity, you will use soap to mimic the action of bile. Soap is unique in that a soap molecule has a polar (charged) end and a non-polar (non-charged) end. The non-polar end grabs onto grease, oil, or fat, while the polar end grabs onto a polar substance such as water molecules. In this way, it is able to separate lipid molecules.

Procedure:

1. Given the following research question, How does the presence of dish soap affect the emulsification of oil?, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below______________________________________________________________________________

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2. Obtain TWO clean test tubes (no soap or oil). Label them.

3. Fill BOTH tubes 1/3 full with water and 1/3 full with vegetable oil.

4. Make a labeled drawing of your observations after doing this.

5. To one tube, add about 1cm of soap.

6. Cover the openings of BOTH test tubes with your hands/fingers and shake vigorously.

7. Draw a picture of each test tube after shaking.

8. Clean your materials at the sink using soap and water and a test tube brush. Hang the test tubes to dry on the drying rack before moving on to the analysis questions.

Table 3: Observations for oil emulsification.

Test Tube Before Shaking Test Tube After Shaking(- soap)

Test Tube After Shaking(+ soap)

Analysis Questions:


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2. Which is less dense, oil or water? Justify your response.

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3. How are the test tubes different after shaking with the detergent?

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4. Explain chemically why water and vegetable oil do not mix.

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5. Detergents act as an emulsification agent. Explain what this means (you may need to read the introduction to this activity again) and how detergents dissolve lipids like vegetable oil.

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6. If bile is not an enzyme, then how does it help digest food?

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7. What kind of foods would bile help to digest?

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8. Homes having hard water (which often contains more dissolved calcium) require more detergent to efficiently wash clothing. Explain this observation based on your knowledge of the chemical structure of detergents. The diagram below may be helpful to your response.

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Station 4:Molecular Motion and Polarity

Introduction:

Polarity refers to the separation of electric charge leading to a molecule or its chemical groups having a dipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in electronegativity between atoms in a compound and the asymmetry of the compound's structure. A molecule of water is polar because of the unequal sharing of its electrons between oxygen and hydrogen in which the former has larger electronegativity than the latter. This results in water having a "bent" structure. Polarity underlies a number of physical properties including surface tension, solubility, melting- and boiling-points, and molecular motion.

All molecules are in constant motion. Molecules of a liquid have more freedom of movement than those in a solid. Molecules in a gas have the greatest degree of motion. In a liquid state, molecules will exhibit motion that is also dependent on their affinity for water.

In this activity, explore the polarity of milk by observing the behaviors of water (food coloring) when added to whole milk.

Procedure:

1. Given the following research question, How does the polarity of milk affect the ability of water to mix in its liquid state?, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below.

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2. Safety Precautions: FOOD DYES MAY STAIN SKIN OR CLOTHING…

3. Pour enough milk into the Tupperware dish to cover the entire surface about ¼ inch deep.

4. Add one drop of each different color food dye to each half of milk in the pie plate. Be careful not to mix!

5. Draw a picture of what you see.

6. With a single toothpick, add a small amount of detergent into the center of the Tupperware dish containing milk. Hold the toothpick still and wait to see what happens.

7. Draw a picture after adding the detergent.

8. Specifically state the results of the experiment.

Table 4: Observations of molecular motion and polarity before and after the addition of dish soap.

Results Before Adding Detergent Results After Adding Detergent

Analysis Questions:


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2. In one or more paragraphs, explain your observations. Please address the following in your explanation:

a. A rationale for the food coloring floating initially in organized blobs on the surface of the milk.

b. Changes in the surface tension of the water in the milk.c. Changes in the intermolecular forces involving the proteins in the milk.d. The structure of the molecules making up the detergent.

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Station 5:Celery Sprint and the Paper Towel Race

Introduction:

Trees must transport water and minerals to their highest leaves. How does this happen? Interestingly, trees move water by losing water. Transpiration is the evaporation of water from plants from the surface of the leaf through tiny pores called stomata. Inside the plant, a thin layer of water covers the cell wall, as the water evaporates from the leaves, water and minerals are pulled up the stem to the leaves, thus allowing water to reach the highest leaves of a tree. Similarly, water is able to travel through the narrow spaces between the fibers of the paper towel (also made of plant material), a phenomenon called capillary action.

With this information in mind, investigate the phenomena of transpiration in celery and capillary action in various brands of paper towel.

Procedures:

1. Given the following research question, Which brand of paper towel will have the fastest rate of capillary action?, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below.

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2. Observe the stalks of celery that have been set up at different periods of time in beakers containing colored water. Record your observations in the space provided below.

3. Cut your THREE brands of paper towel into 1 x 4 inch strips.

4. Tape the three strips side-by-side to a pencil.

5. Dip the paper towel samples into the bowl of water simultaneously, and hold your hand steady.

6. Record your results in the space provided in the class handout. Which paper towel was saturated the fastest?

7. When you are finished, create an annotated drawing in your water foldable illustrating how water moves up the trunk of a tree.

Table 5: Observations of water movement through the celery stalk after different amounts of elapsed time.

Time _____ hours _____ hours _____ hours

Observations:

Table 6: Observations of water movement through the types of paper towel.

Time Paper TowelBrand 1

Paper TowelBrand 2

Paper TowelBrand 3

Time:

Observations:

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Analysis Questions:


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2. Explain how water moves up the celery? Incorporate the properties of water into your explanation.

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3. Explain how water moves up the paper towel? Incorporate the properties of water into your explanation.

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4. Why does the water move at differences speeds up the different sources of paper towel?

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Station 6:Floating Paperclips and Sinking Pepper

Introduction:

Aluminum should sink because it has a density that is greater than that of water (aluminum is 2.7 times more dense than water). However, when an aluminum paperclip is placed on the surface of the water, it will often float.

Procedure:

1. Devise a research question that you would like to investigate in relation to the floating paperclip. For example, “Will the paperclip still float if I drop it on the water from above?”. Then, write your hypothesis to answer this question using the VCR method.

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2. Drop a paperclip in a beaker of water. Record what happens in your class handout.

3. Tear off a piece of paper towel that is slightly larger than the paperclip.

4. Place the piece of paper towel on top of the water.

5. Gently place another paperclip on the piece of paper towel. Wait a few seconds. If necessary, gently submerge the piece of paper towel with the tip of your finger. Record what happens to the paperclip in your class handout.

6. In a second beaker of water, sprinkle pepper. Record what happens in your class handout.

7. Using a toothpick, add a drop of liquid dish detergent to the beaker of water. Record what happens to the pepper in your class handout.

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8. Using the same toothpick, add a drop of liquid dish detergent to the beaker with your paperclip. Describe what happens to the paperclip in your class handout.

9. Clean your materials. Rinse out the beakers, and wipe dry with clean paper towel. Refill the beakers with fresh water.

Table 7: Observations on the effects of dish soap on the floating of various articles.

Paperclip PepperPre-Soap Post-Soap Pre-Soap Post-Soap

Analysis Questions:

1. What emergent property of water (or properties) is being evaluated with this experiment? Explain.______________________________________________________________________________

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2. How do you think the water is keeping the paperclip from sinking?______________________________________________________________________________

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3. What happens if you put the paperclip on the water by a different method?______________________________________________________________________________

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4. Why does pepper NOT float on the surface of the water after you added the soap?______________________________________________________________________________

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5. Devise a research question that you would like to investigate in relation to the floating paperclip. For example, “Will the paperclip still float if I drop it on the water from above?”. Then, write your hypothesis to answer this question using the VCR method.

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Station 7:Demonstration of Solvent Ability

Introduction:

Consider a can of soda: it’s a solution of sugars or sugar substitutes, flavoring, and carbonation. This makes the point that water is a very versatile solvent; that is, water can dissolve many other substances. In fact, water is sometimes called the “universal solvent.” Your cells are essentially small packets of water that contain a complex solution of molecules dissolved within the water. Substances that dissolve in water or are attracted by water are called hydrophilic. And guess what? This property is also the result of water “sticking” to hydrophilic substances. Of course, not all substances dissolve in water. Two substances you are familiar with that do not dissolve in water are waxes and oils. Water beads up on waxy surfaces and the oil in salad dressing rises above the watery vinegar. Substances that do not dissolve in water or repel water are called hydrophobic. Both hydrophilic and hydrophobic substances can be found in living systems.

Procedure:

1. Given the following research question, Which solids, ionic or covalent, will water be able to dissolve faster?, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below.

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2. Using a sectioned reaction dish, place 1mL of the polar liquid into two sections, and 2ml of the nonpolar liquid into two sections.

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3. Using a mass balance, measure two 0.5g portions of the ionic solid (NaCl) and two 0.5g portions of the covalent solid (sucrose). Add 0.5g of the ionic solid to the first polar section and the first nonpolar section. Add 0.5g of the covalent solid to the second section of the polar liquid and the second section of the nonpolar liquid.

4. Record the start time in Table 8.

5. Gently swirl the reaction dish so that the liquid in each of the sections can dissolve the solids. Record your observations for each sample.

6. Record the time it takes for each of the solids to dissolve in each of the solvents. Note: The solids in some sections may never dissolve entirely.

Table 8: Addition of ionic and covalent solids to polar and non-polar solvents.

Pola

r Sol

vent

Ionic Solid Covalent SolidStart Time: Finish Time: Start Time: Finish Time:

Observations: Observations:

Non

-Pol

ar S

olve

nt

Ionic Solid Covalent SolidStart Time: Finish Time: Start Time: Finish Time:

Observations: Observations:

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Analysis Questions


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2. Which liquid was a greater solvent?

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3. Using a diagram and a written description, explain how the electronegativities of this molecule increases its solvent ability.

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4. Using your results from this test, make one inductive conclusion about the solvent ability of polar and non-polar liquids.

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Station 8:“Fire burn and cauldron bubble” – Macbeth, Act 4, Scene 1

Introduction:

One of the most important properties of water for the environment is its ability to moderate temperature. Unlike most common substances, water can absorb a lot of energy with only small changes in temperature. Here’s a mind experiment that makes this point: In your imagination, place a pan of water on the stove and turn the burner to high. Wait 30 seconds. Which would more likely burn you at this point: the pan made from steel or the water inside it? You can probably guess that the pan reaches burning temperatures much faster than the water does. This demonstrates that water resists changes in temperature more than steel does.

Water’s ability to absorb heat is the result of the sticky nature of water. Before the temperature can increase in water some energy is absorbed to overcome the stickiness—to separate water molecules from each other. Energy is therefore put into breaking the hydrogen bonds between waters rather than raising the temperature. A consequence of this property is that water can reduce temperature swings for the planet as a whole and also in specific environments near large bodies of water. Oceans have remarkable abilities to keep the air temperature around them from changing a lot. For example, in Seattle or Boston, which are both along seacoasts, the temperatures rarely get above 100 degrees Fahrenheit or below zero. On the other hand, cities in the U.S. heartland, such as Minneapolis or Omaha, experience these temperatures on a yearly basis. Without the huge oceans, Earth’s temperatures would not be compatible with life as we know it.

Procedure:

1. Safety Precautions: BOILING LIQUIDS AND HOT PLATES MAY BURN THE SKIN…

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2. Given the following research question, How does the presence of ethyl alcohol affect the boiling point of a solution?, develop a hypothesis in the VCR format that answers the research question. Write your hypothesis below.

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3. Set each hot plate at setting “8”. Onto each hot plate place either a beaker containing 250 mL of room temperature water or room temperature ethyl alcohol.

4. Plate a thermometer into each beaker. Record the starting temperature and temperature at which each liquid comes to a boil.

Table 9: Boiling points of various liquids.

Water Ethanol

Starting Temp (°C)

Temp at Boiling (°C)

Analysis Questions:


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2. Explain why water has a high heat of vaporization.

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3. Explain why children in summer can cool off by playing in a sprinkler.

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honors bio - homensaapbiology.weebly.com/.../2012-09-10_properties_of_… · web view2012/09/10...

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