Pogil Properties of Water - Answer Key

Properties of Water What Makes Water So Special? Directions: Remember to answer the following questions using a different color font. Why? _________________________________________________________________________________ When you hear that NASA’s space probes are looking for “evidence of life” on other planets, do you know what that means? They are looking for evidence of liquid water. Water is fundamental for all life; without it every living thing would die. Water covers about 70% of Earth’s surface and it makes up 65–75% of our bodies (82% of our blood is water). Even if water might seem boring to you—no color, taste, or smell—it has amazing properties that make it necessary for supporting life. _________________________________________________________________________________ Model 1 - The Molecular Structure of Water 1. How many hydrogen atoms are in a molecule of water? There are 2 hydrogen 2. How many oxygen atoms are in a molecule of water? There is 1 oxygen 3. What holds the hydrogen atoms to the oxygen atom? The covalent bonds 4. The shading around the molecule represents the relative density of electrons shared by the atoms. What does this indicate about the density of electrons around the oxygen atom as compared to the density of electrons around the hydrogen atoms? The bond around the oxygen is stronger than the bond around the hydrogen 5. Where is the majority of negative charge on the water molecule? It is the oxygen atom Model 2 - Attraction of Water Molecules 6. Looking at your answers to Questions 1 and 2 from Model 1, tell what atoms are represented by: a. The small, unshaded circles in Model 2. They are hydrogen atoms b. The larger gray shaded circles in Model 2. They are oxygen atoms 7. What do the solid lines between the small and large circles represent? The covalent bonds is the solid lines 8. According to Model 2, what is represented by the dotted lines? The weak attractions is the dotted lines 9. Remember that electrons in a water molecule are more dense around the oxygen atom and less dense around the hydrogen atoms. a. What kind of charge would the oxygen atom have compared to the hydrogen atoms? They have Negative charges b. What kind of charge would the hydrogen atoms have compared to the oxygen? They have Positive charge 10. Describe the arrangement of the water molecules in Model 2 with one another. Between the water molecule the hydrogen atom is connect to the oxygen atom 11. Describe the cause of the attractions between molecules of water. Oxygen has higher electronegativity so the hydrogen bonds will connect more towards the oxygen atom 12. If another water molecule was added to the group in Model 2 at the upper right side, which of its atoms would be connected to the existing molecule with a dotted line? Describe your group’s reasoning. The hydrogen atom of the new molecule will connect to the closest existing oxygen atoms because we observe that the other hydrogen atoms are connected to the oxygen atom. The oxygen has a negative charge while hydrogen has a positive charge. Read This! _________________________________________________________________________________ The bonding electrons in some molecules are not equally shared between the atoms. These neutral molecules with a difference of charge across the molecule are called polar molecules. Because of the arrangement of the atoms and electrons in a water molecule, there are two differently charged areas of the molecule even though the molecule is neutral overall. The hydrogen molecules are slightly positive, while the oxygen is slightly negative. The positive area charge (hydrogen) of one water molecule is attracted to the negative area (oxygen) of a different water molecule. This weak attraction is often referred to as hydrogen bonding. _________________________________________________________________________________ 13. In the space below, copy, then paste 10 water molecules to create a cluster. SKIP Extension Questions 14. Other polar molecules include nucleic acids and some proteins. Look at the DNA sketch provided and predict how the two strands are attracted to one another. One strand has a slightly negative area and one strand has a slightly positive area. 15. Some molecules that are covalently bonded do not have a difference in charge across the molecule. These molecules are referred to as nonpolar. What arrangement of electrons would result in a nonpolar molecule? There would be no positive strand area and negative strand area 16. Some examples of nonpolar molecules include fats, oils, and waxes. How do these substances interact with water? They don't mix with each other 17. What prediction would you make about why oil and water interact in the way described above? Oil is more dense than water