Sticky Molecules Gizmo Answer Key

Name: Lewis Leonard Date: 12-14-2022 Student Exploration: Sticky Molecules Directions: Follow the instructions to go through the simulation. Respond to the questions andprompts in the orange boxes. Vocabulary: adhesion, capillary action, capillary tube, cohesion, hydrogen bond, intermolecular force, molecule, newton, nonpolar, partial negative charge, partial positive charge, polar,surface tension, tensiometer Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. James adds some magnetic marbles to a glass jar full of ordinary marbles, and then shakes up the jar. What do you think will happen to the magnetic marbles? Because metal does not attract to glass, I believe the magnetic marbles won't linkto the regular marbles. 2. James then dumps the marbles on a steel cookie sheet and tilts it. Which type of marble will roll off more easily? Ordinary because glass marbles roll off more quickly since they lack a magnetic field. Gizmo Warm-up Just as some marbles are attracted to one another while others are not, certain molecules stick together more than others. In the Sticky Molecules Gizmo, you will discover what causes this “stickiness.” You will investigate a variety of phenomenathat result from the attraction of molecules to one another. To begin, drag a dropper bottle of Water and a Petri dish (labeled Polarity ) to the simulation area. Drag the dropper over the dish to add water. Examine the molecules. 1. What do you notice about the water molecules? The water molecules are both moving apart and toward one another. Combining parts Hand O (electric charge). Different areas of the water molecules are electrically charged. The red portions of the molecules arenegatively charged, while the blue regions are positive. Purple is neutral. 2. Note the yellow lines which show attractions between the molecules. Why do you think these attractions occur? Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

The positive and negative charges cause them to attract to one another, which causes thisattraction to happen. It acts magnetically. Activity A: Polarity Get the Gizmo ready: ● Check that the Petri dish contains water. Introduction: All molecules are neutral overall. However, the charges within molecules are not always arranged in the same way. In a polar molecule the positive and negative charges are separated into distinct regions. In a nonpolar molecule the charges are evenly dispersed. Question: Are polar or nonpolar molecules more “sticky?” 1. Classify: Based on what you observe, are water molecules polar or nonpolar? Polar Indicate your choice in the data table using the drop-down menu. The presence of charged regions indicates a polar molecule. However,these charged regions do not represent full charges as found incompounds such as sodium chloride. Instead they are partial positive (δ+) and partial negative (δ–) charges, which are much weaker than full charges. 2. Hypothesize: Note the yellow lines that form between molecules, which represent hydrogen bonds . A hydrogen bond (H-bond) is an example of an intermolecular force (IMF). IMFs occur between all molecules, but hydrogen bonds are the strongest. A. What causes these H-bonds to form? (Hint: Look at the charged regions.) These H-bonds are generated by the electron attraction. B. Why do you think the H-bonds only last a short time before breaking and reforming? It's possible that the ties are flimsy, which would make them break quickly. 3. Explore: Replace water with hexane (an ingredient in paint thinner). Examine the molecules. A. Do you see any charged regions? No Do any H-bonds form? No B, Is hexane polar or nonpolar? Non polar Indicate this in the data table. C. Observe and classify the other two liquids. Which one is polar? Glycerin Which one is nonpolar? mineral oil Indicate this in the data table. 4. Summarize: Molecules that are attracted to one another can be called “sticky.” Which types of molecules, polar or nonpolar, are the “stickiest”? Polar molecules Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

What causes this stickiness? The molecules cling togetherand become sticky due tocohesive force. H-bonds makethings sticky. Activity B: Cohesion andadhesion Get the Gizmo ready: ● Drag the Drop diameter tool (a piece of wax paper) to the simulation area. Introduction: When molecules of the same substance stick together, cohesion occurs. When molecules of different substances stick together, such as a drop of liquid to a solid surface, adhesion is taking place. Both cohesion and adhesion occur due to intermolecular forces of attraction. Cohesive forces tend to be strongerthan adhesive forces. Question: How can the strength of cohesive and adhesive forces be determined? 1. Predict: All drops do not look the same—some are rounded while others are flatter. A. Do you expect polar or nonpolar liquids to form the roundest drops? Polar liquids should be more rounded, and nonpolar liquids should be flatter. B. Explain your reasoning. The magnetic link that polar molecules share is the primary cause. Because non-polarmolecules have weaker attractive forces, they cannot maintain their form. 2. Measure: Drag the dropper bottle of water to the simulation area. Add a drop of water to the wax paper. The drop holds together and assumes its shape due to cohesive forces. A. Describe the shape of the water drop. oval and centered B. Use the ruler to measure the diameter of the drop. What is its diameter? 6 mm Enter this measurement in the data table. 3. Analyze: Measure the drop diameter for each of the other substances. A. Enter these values in the data table and then record below: Hexane 19 mm Glycerin 5 mm Mineral oil 8.5 mm B. Was the prediction you made in 1A confirmed? Yes C. How do the drops of polar liquids differ from those of nonpolar liquids? Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

While the nonpolar liquid glycerin was similarly circular and was smaller than water, thedroplets for the polar liquid were flawlessly round and measured a perfect 5mm. Othernon-polar fluids had no form, were flat, and dispersed across the drop diameter. D. How do intermolecular forces affect the shape of a drop? Intermolecular attractive interactions between water molecules cause the droplet toadopt a spherical shape. 4. Predict: Drag the Tilt angle tool to the simulation area. Adhesive forces can be measured using this instrument, which can be tilted to form an inclined plane. The greater the adhesion, the greater theangle at which it can be tilted before the drop begins to slide. Which substances do you think will experience the greatest adhesive force? Why? Because it requires a greater angle to drag down, the polar molecule will have thestrongest adhesion. 5. Investigate: Drag the dropper bottle of water to the simulation area. Add a drop to the tilt angle instrument. Using the slider, gradually increase the incline until the drop starts moving. A. At what angle does the drop begin to slide? 18 Enter this value in the table. B. Repeat the above procedure with the other substances. Enter the angle at which each droP begins to slide in the data table, and then record below: Hexane 9 Glycerin 12 Mineral oil 8 C. As the angle increases, do polar or nonpolar molecules tend to slide first? 6. Explain: To understand adhesion, consider the charges on the surface of the inclined plane. Since it is nonpolar, the positive and negative charges are evenlydistributed, as shown to the right. The negative charges (electrons) can freelymove, while positive charges (protons) tend to be fixed in place. A. If the positive end of a water molecule were to encounter the surface shown above, what might happen to the surface’s negative charges? Explain your reasoning. The water droplet will remain adhered to the surface due to the negative charge of thesurface. This means that positive and positive charges repel one another whereasnegative and negative charges repel one another. B. On the image at bottom right, draw in the charges after a water molecule contacts the surface. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

C. How does this explain why polar molecules have better adhesion than nonpolar molecules? It explains why polar molecules have stronger adhesion forces thannon-polar ones. Activity C: Surface tensionand capillaryaction Get the Gizmo ready: ● Drag the Surface tension tool ( a tensiometer ) to the simulation area. Introduction: Cohesion and adhesion give rise to a variety of phenomena. Surface tension represents the force exerted by the surface of a liquid. Capillary action occurs when a liquid creeps up the sides of a thin tube, in apparent defiance of gravity. Question: How do intermolecular forces create surface tension and capillary action? 1. Predict: A tensiometer contains a ring immersed in a liquid. A sensor connected to the lever registers the force needed to lift the ring out of the fluid. The greater the surface tension of the liquid, the greater theforce required to lift the ring out of the fluid. In which substances would you expect to see greater surface tension? Why? Due of the shared magnetic connection. 2. Experiment: Drag the dropper bottle of water to the simulation area. Add some water to the dish. Pull down on the lever until the ring breaks free from the surface of the water. Note that the force is measured in unitsof millinewtons (mN). 1 mN = 1/1000 of a newton (N). A. How much force was required? 33 mN Enter the measurement in the data table. B. Repeat this procedure with the other liquids. Enter the force required to break the surface tension in the data table, and then record below: Hexane 13 mN Glycerin 35 mN Mineral oil 17 mN C. Do polar or nonpolar liquids have greater surface tension? Polar liquids. D. Explain how polarity affects surface tension. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

A liquid's subsurface molecules are drawn to the molecules all around them.Because water molecules are attracted to one another strongly, the substancehas a high surface tension. 3. Compare: Examine the measurements for drop diameter in the data table. What is the relationship between surface tension and drop diameter? They demonstrate the molecule's ability to remain condensed and not disperse. Surface tension is responsible for a drop’s rounded shape, with cohesive forces holding itsmolecules together. The interior molecules are pulled equally in all directions, but those on thesurface are only pulled inward. As a result, the drop shrinks to the shape with the smallestpossible surface area, which is a sphere. 4. Investigate: Drag the Capillary rise tool (a capillary tube ) to the simulation area. Fluids have a tendency to rise up into these thin glass tubes due to capillary action. A. Which liquids do you think will rise the highest? The polar liquids. B. Drag the dropper bottle of water to the simulation area and add water to the dish. Make sure the tube diameter is set to 1 mm. Measure the height of the water. How high did it rise? 22 Enter this measurement in the data table. C. Repeat this procedure with the other liquids. Enter the capillary rise in the data table, and then record below: Hexane 11 Glycerin 18 Mineral oil 14 D. What patterns do you see? Once more, polar liquids are superior to non-polar liquids. Capillary action depends on the balance between cohesion and adhesion. In order for a liquid torise up a tube, the force of adhesion between the liquid molecules and the sides of the tube must bestronger than the cohesive forces within the liquid. 5. Explore: Select Water . Use the Tube diameter slider to adjust the width of the tube. A. How do you think the width of the tube might affect how high the fluid rises? Larger openings have less surface area and more molecules, making it moredifficult for molecules to remain in place. B. Adjust the width of the tube. Why do you think width affects capillary rise? Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

There is less surface for the molecule. 6. Summarize: Use the arrows beneath the data table to adjust the columns so the polar substances are grouped together and the nonpolar substances are grouped together. A. What do the polar substances have in common? They can adhere to surfaces more readily because they have a stronger intermolecularforce of attraction. B. What do the nonpolar substances have in common? They do not adhere to surfaces readily because they have weak intermolecular forcesof attraction. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved