Biology Homework Chapter 2: Water Properties
Reading Assignment in Textbook
Textbook assignment: Chapter 2: The Chemical Basis of Life, sections 10-16. Review your understanding of the whole chapter by reading through the chapter view on p. 30 and do a mental self-test with the multiple choice questions on p. 31. Identify those which you cannot confidently answer and check the chapter sections for the information you need. If it still doesn't make sense, be sure to raise your questions in class.
- 2.10 Hydrogen bonds are still weak bonds (compared with strong ionic bonds and still stronger covalent bonds), but if there are lots of them, the amount of energy required to break them grows. Hydrogen bonds are responsible for some of the peculiar properties of water, for the folded structure of proteins, and for the reproducibility of DNA, so be sure that you understand this concept.
- 2.11 Water has a high boiling point (boils at a high temperature) because the hydrogen bonds between its molecules must be broken. Alcohol has a low boiling point; it is a covalent molecule with no hydrogen bonds to hold its molecules together. Water can thus absorb a lot of heat without evaporating, so large bodies of water become "heat sinks".
- 2.12 Density is a measure of the amount of matter you can pack into a given volume. When water becomes ice, the structure of the ice crystals takes up more room than the same molecules in liquid form, so ice, being less dense than liquid water, floats on its surface. Ice can then serve as an insulation barrier for water below it—preventing lakes from freezing solid even when the temperatures of the air are far below zero.
- 2.13 Be sure that you understand the terms here. A solution is (usually) composed of a liquid solvent in which a solid solute dissolves (but not always: you can have solutions where both components are liquids or even solids—brass is a solution of tin and bronze— so you pick one to call the solvent). Polar molecules like water are good solvents for other polar molecules or atoms held together by ionic bonds, but don't work as good solvents for non-polar molecules like gasoline—which is why water and gas don't mix.
- 2.14 This section introduces another basic concept for all life processes. Most life processes occur in cells filled with various chemicals dissolved in water, in particular, and many of these involve the exchange of protons between acids and bases. My weblecture covers the definition of the log scale in more detail.
- 2.15 Carbon dioxide dissolved in water makes it more acidic (pH goes from neutral 7 to acid 1 or 2, depending on the concentration). Acids can dissolve calcium carbonate and destroy organic structures that depend on this compound, including coral reefs.
- 2.16 Our definition of life, especially the formation of cellular structure and the metabolic processes underlying growth and inheritance, require the presence of liquid water. For this reason, the discovery of water in any form on a planet is important: it is a pre-requisite to finding extraterrestrial life.
Read the following weblecture before chat: The Chemical Basis of Life: The Special Properties of Water
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Use the pH scale interactive below to gain a better understanding for how pH is used to measure acidity.
- Use the Macro exercise to make the following observations.
- Use the dropdown menu to select orange juice as the additional component. The tank will fill with 0.5L of orange juice. What is the pH of this solution? Is it an acid or a base?
- Add water until you have a 1.0L volume. What happened to the pH of the solution?
- Experiment with other solutions. What happens if you start with a smaller amount of acid or base and add a large amount of water?
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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