Stations 1-­‐6 The USGS website below is a great place to start for water vocab which should also lead you into some interesting experiments. Using the data that you collected doing the labs last Wednesday, can you write up your observations and about the stations 1-­‐6 (number each response) in a 1-­‐2 page description. You may use the information below and research the website too. http://water.usgs.gov/edu/capillaryaction.html 1) Solubility is the ability of one substance to dissolve another substance. (Remember: the chemical being dissolved is the solute and the chemical doing the dissolving is the solvent!). Water is a good solvent, especially for ionic compounds – salt is an ionic compound. Ions have to be able to dissolve quickly in cell fluids for cellular metabolism (the energy pathways of a cell) to work properly! As a matter of fact, water is called the UNIVERSAL SOLVENT. 2) Surface Tension – Cohesion and Adhesion Because each water molecule is polar, the water molecules are highly attracted to one another. This is especially true at the surface, where the water is much more attracted to itself than it is attracted to the air…It almost seems like water can form a skin on the surface…this is called surface tension. Surface tension is really a combination of: the attraction between molecules of water = cohesion = water sticks to water = think: “water attracted to water” & the molecular attraction between water molecules and other substances = adhesion = water sticking to something else…think: “adhesive tape”! 3) and 4) Water is a polar substance which leads to it have two properties, cohesion and adhesion. Cohesion describes how water molecules are attracted to each other and stick together. Adhesions describe how water molecules are attracted to other substances and sticks to them. •
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5) Density of Water Typically solid things sink because they are denser than the liquid that they are placed in. Record your observations of what solid oil does in liquid oil. Ask yourself, which is denser solid or liquid oil? Now, let’s do this with water because water behaves differently. Place the solid water (ice) in liquid water. If you don’t already have solid water, then get some from the ice bucket. Record your observations of what solid water does in liquid water. Ask yourself: Which is denser water or ice? Answer the following questions: 1. In order for the ice to have floated, what had to have happened to the molecules of water when they water froze? 2. How has the fact that solid water floats instead of sinks have affected the evolution of life on Earth? 3. Describe some examples of organisms taking advantage of this special property of solid water. 6) Capillary Action • Noting how fast the water climbs up the paper towel demonstrates capillary action. Water uses the property of capillary action to move from one place to another. Capillary action occurs because water is sticky, thanks to the forces of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances). Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact. Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules. The height to which capillary action will take water in a uniform circular tube (picture to left) is limited by surface tension and, of course, gravity. From USGS
Organizing Your Knowledge
Describe at least one observation you have made at some point
in your life that demonstrates each phenomenon as it relates to
water:
Polarity
Hydrogen bonds
Cohesion
Surface tension
Adhesion
Capillary action
Dissolving
Density
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Phases of Matter -­‐ lab idea • Water is unique in that on Earth it exists in three states of matter. This is due to the temperature and atmospheric pressure on Earth. • Observe water in its three states. Describe them and collect some quantitative data about temperature. Compile a data table that shows the relationship between the state of matter and the temperature. • Answer the following questions:
1.
We call room temperature on Earth 20-­‐25°C. Using your data table, determine the state of matter water exists at in room temperature. 2.
The room temperature of Mars is -­‐60°C. Based on your table what state of matter would water exist at on Mars?
3.
4.
5.
Venus has a room temperature of 460°C. Based on your table what state of matter would water exist at on Venus?
How has having liquid, solid and gas water affected the evolution of life on Earth? How does it explain the lack of life on other planets?
Titan, a moon of Saturn, has flowing rivers of liquid methane, frozen glaciers of methane, and methane clouds in its sky. On Earth methane exists in its gas phase unless it is artificially frozen or pressurized into a liquid. How might life evolve on Titan with methane as life has evolved on Earth with water?
The Meniscus -­‐ another lab idea • Because of adhesion and cohesion water in a cylinder creates a bend at the water line called the meniscus. • Fill a graduated cylinder with water.
• Draw a picture of the water line and label the meniscus. • Stand up and try to read measure the water in the cylinder. Write down your reading. • Pick up the cylinder and hold it above eye level. Take a reading from this viewpoint. Record it. • Set the cylinder back down and squat down till your eyes are level with the water line. Record your reading. • Answer the following questions. 1. Which method gave you the most accurate reading? 2. What property of water makes it curve up along the sides of the cylinder? 3. What property of water makes it curve down in the center? 4. How might these properties have played a role in the formation of life on Earth? (Hint: ponds are just big /shallow graduated cylinders. 5. How do these properties affect biological science now? (Hint: biological science= the study of life… think lab and experiment wise) Capillary Action -­‐ another lab idea Water uses the property of capillary action to move from one place to another. • Use a paper towel to demonstrate how you can transfer the colored water from one cup to the other without touching the cups or handling the water. • Draw a picture of your setup. • Answer the questions. 1. How long do you think it would take to transfer all of the water?
2.
How could you speed up the process?
3.
What relationship does capillary action have with life on Earth?
4.
How might this property been involved in the evolution of life? Hydrophobicity and Hydrophilicity Watch the downloaded video “Capillary Action” this title is misleading… I actually think it is a mistitle on the part of the creator but none the less the video shows two very important aspects of water’s influence of life here on Earth, hydrophobia and hydrophilia. Feel free to skip the beginning where he talks for forever. • After the video use Safari and what you saw in the video to answer the following questions. 1. What does it mean when a particle is hydrophobic? What about hydrophilic? 2. How might this have played a role in the evolution of life on Earth? 3. Find three examples of hydrophobicity or hydrophobicity in a biological system (think living thing!) List the examples and how they show the properties of hydrophobicity and hydrophilicity. Diffusion lab idea • At this station there are three beakers of water. Create a data table on your lab report that shows the temperature of the water and diffusion rate. • Use a thermometer to record the temperature of each water beaker. • Place one drop of food coloring into each beaker. Use a qualitative descriptor term (fast, medium, slow) to record your observations about the rate of diffusion in each beaker. • Use your data table to construct a conclusion about how temperature affects the diffusion rate of molecules in water. Record your conclusion. • Answer the following questions. 1. What is Diffusion? 2. How might the property of diffusion in water have influenced the evolution of life on Earth? 3. Since water is the majority molecule found in living organisms, how might body temperature affect diffusion in organisms?