AP Chapter 3 Study Guide: Water
(Rob Hamilton © 2011)
Teacher’s Note: Chapter 3 contains some simple concepts concerning the importance of water to living things. You will probably remember most of this stuff from biology I, but don’t be careless. Free response questions concerning water have been found on the AP biology exam. The chapter also includes material concerning molar concentration and acids & bases. This stuff is of secondary importance and we will treat it that way. Don’t panics if you haven’t had chemistry and molar concentration and acids & bases give you trouble! The bald man & the nice lady across the hall will do a lot better job (and spend much more time) teaching you these concepts. So read pgs 46-52(it is a relatively quick and easy read) and answer the following questions:
1. Water is a polar molecule. What does this mean? (You must use the word electronegativity in your answer.)
______
______
2. What is a hydrogen bond? (You must use the word electrostatic in your answer). ______
______
3. How does cohesion differ from adhesion? ______
______
4. In a plant, the leaves which need water for photosynthesis may be meters away from the roots which absorb
water from the ground. Explain how water’s properties enable it to move against gravity from roots to leaves.
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______
______
5. What is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by
1oC?______.
6. Water has a high specific heat? How does hydrogen bonding produce this property?______
______
7. When you get hot, you sweat. However, sweat on human skin does NOT (in and of itself) produce a cooling
affect. Describe specifically how sweating cools the body. (a molecular level explanation is required)
______
______
8. When you place an ice cube in a glass of water, does it sink or float? ______
Why? ______
9. What would happen to aquatic life if ice sank when it froze? ______
______
Many molecules that are important to living things easily dissolve in water. Plasma transports these compounds in many animals and sap transports them in plant. Read pgs 50-52 and we will define a few terms and then introduce molarity.
10. What do we call a substance (like water) that can dissolve another substance? ______
11. What do we call the substance that gets dissolved? ______
12. What do we call a mixture in which a solute (such as salt) is dissolved in a solvent (such as water?)
______
13. What is a hydration shell? ______
14. Why will a hydration shell form around salt or sugar, but not around fat or oil? ______
______
15. What term do we use to represent substances that are polar or ionic that will easily dissolvein water?
______(Hint: it means water loving in Greek)
16. What term do we use to represent substances that are non- polar and will not dissolve in water?
______(Hint: it means water fearing in Greek)
17. Your cells contain a lot of water. Therefore, your body which is made of cells contains a lot of water.
Would you predict that your cell membranes and skin are composed of hydrophilic or hydrophobic
molecules? ______
Okey Dokey….here is where the excrement hits the bladed cooling appliance. The authors provide a fairly straight forward description of molarity on pgs 51-52, but they never explain why this is done. I will do my best to provide a quickie reason why. Here we go………Imagine that we must determine the mass of a marble, but we only have a bathroom scale. I place a marble on the scale and it reads 0. We know that this cannotbetrue because obviously our marble has some mass, but unfortunately our instrument is not calibrated precisely enough to measure it. The solution to this problem is to keep adding marbles until the scale can measure it and then divide by the number of marbles on the scale. The same problem occurs when we try to measure the mass of a single atom or molecule on a gram balance! A guy named Avogadro determined that if he placed 6.02 x 1023 atoms of hydrogen on his balance, it would weigh 1g. It turns out that 6.02 x 1023 atoms or molecules of a substance is the number needed to be the molecular weight in gramsof that substance and we call 6.02 x 1023 atoms or molecules a mole!
I will hold your hand through the problem below:
18. Glucose has the molecular formula of C6H12O6. First we must figure the molecular weight of glucose in Daltons. Do the math
The atomic mass of carbon is ______X 6 carbons = ______
The atomic mass of hydrogen is ______X 12 hydrogens = ______
The atomic mass of oxygen is ______X 6 oxygens = ______
The molecular weight of glucose is ______Daltons
A mole equals 6.02 x 1023 molecules so 1 mole of glucose weighs ______grams
If we want a 1 molar solution of glucose, we would dissolve 180g of glucose in water and bring the total volume to a liter.
19. Now it is your turn to fly on your own. Describe how you would make a 1 molar salt (NaCl) solution below:
Every now and then, a hydrogen participating in a hydrogen bond between two water molecules will be pulled to the oxygen atom of the other water molecule, leaving its electron behind. This reversible reaction can be written as follows: H2O ↔ H+ + OH-. Read about acids and bases on pgs 52-56
20. A single proton, H+, with a positive charge is called ______
21. The water molecule that lost the proton, OH-, has a negative charge and is called a
______.
This is a rare occurrence, only one molecule of water is disassociated per 554 million water molecules. Thus, at 25oC, the number of hydrogen ions (H+) and hydroxide ions (OH-) is equal at 10-7 M. The concentrations of hydrogen ions and hydroxide ions are exactly inverse! Increase one and you will decrease the other.
22. How do acids effect the hydrogen ion concentration of a solution? ______
23. How do acids effect the hydroxide ion concentration of a solution? ______
24. How do bases effect the hydrogen ion concentration of a solution? ______
25. How do bases effect the hydroxide ion concentration of a solution? ______
In any aqueous solution, at 25oC, the product of hydrogen ions (H+) and hydroxide ions (OH-) is equal at 10-14 .This can be written [H+] + [OH-]= 10-14
26. If an acid was added to water to increase the hydrogen ion concentration to 10-5, what would
be the hydroxide ion concentration? ______What would be the pH? ______
27. If base was added to a solution until the hydroxide ion concentration was 10-3, what would
be the hydrogen ion concentration? ______. What would be the pH? ______
If you cannot do the above problems, go back and actually read pages 53-54. Now do three more problems to prove that you know what you are doing.
28. If the pH of a solution is 6, what is the hydrogen ion concentration? ______.
What is the hydroxide ion concentration? ______
29. If the hydrogen ion concentration to 10-10, what would be the hydroxide ion concentration?
______. What would be the pH? ______. Is this an acid or base? ______
30. If the hydroxide ion concentration was 10-4, what would be the hydrogen ion concentration?
______. What would be the pH? ______. Is this an acid or base? ______
31. What do we call substances that can act as either weak acids or bases and therefore minimize
changes in pH? ______
If you don’t understand...... please ask during class! Otherwise Governor Daniels will replace me with a robot! .