Period+2+Ch.+3+2011


 * AP Biology**
 * Chapter 3 Guided Reading Assignment**

1. Why is water considered a polar molecule? Water is a polar molecule because it has a positive charge on one side and a negative charge on the other side. This happens when the hydrogen shares it's electrons with oxygen, making the hydrogen side positive and the oxygen side negative.



2. For each of the below listed properties of water – briefly define the property and then explain how water’s polar nature and polar covalent bonds contribute to the water special property. Include an example in nature of each property also. a. Cohesion- The binding together of like molecules often by hydrogen bonds. Because of water's polar properties, it continuously changes bonds with neighboring atoms, allowing hydrogen to hold the substance together. In plants, cohesion is used to transport water and nutrients up the stem.

b. Adhesion Adhesion is the attraction between one substance to another and it is caused by the polarity of molecules (positive to negative). Water is particularly know for it's adhesion to other substances. For example, water will cling to surfaces, such as when it climbs up #|a paper towel or cloth.

c. Surface tension - The difficulty to stretch or break the surface. In the presence of air, water uniquely bonds with the air due to hydrogen bonding to almost form another layer of molecules.

d. High specific heat How much #|heat energy it takes to raise the temperature of a unit mass of a substance one degree celsius

ex. boiling water

e. Heat of vaporization The high amount of high that is required to evaporate water (change from liquid to gaseous state); water's hydrogen bonds make it harder to evaporate due to their strength; ex: water vapors from boiling water Letter D is the enthalpy of vaporization f. #|Evaporative cooling The property of a liquid when the surface becomes cooler during evapotation, causing it to lose highly kinetic molecules to the gaseous state. An example would be evaporating of sweat from human skin, which dissipates body heat and helps prevent overheating on a hot day. This relates to the covalent and polarity of water by causing less bonds to break during the reaction into gas. 3. What is special about water and density? Water is special because it is less dense as a solid than a liquid, causing ice to float. Because of this property, oceans, ponds, and bodies of water do not freeze completely through, therefore the ice insulates the water and keeps life from dying.

4. Define the following terms: a. Solute **The substance dissolved in a solution. **

b. Solvent **The mixture of 2 or more substances in which is homogeneous and the solution that something dissolves in. **

c. Aqueous solution a solution in which water is a solvent

d. Hydrophilic Having an affinity to water e. Hydrophobic Repelling water f. Colloid - Molecules which don’t dissolve in water but don’t repel it, resulting in the molecule to be suspended in water. g. Hydration shell The sphere of water molecules around each dissolved ion.



h. Molarity​ "The number of moles of solute per liter of solution" (Campbell) It is used to measure the concentration of a substance within a solution.

5. Label the diagram below to demonstrate the dissociation of the water molecule and then relate this diagram to pH.

The hydrogen in the second water molecule is being attracted to the oxygen of the first molecule. The oxygen of the first water molecule will attract and pull the hydrogen towards itself due to polarity. The Hydrogen that leaves the second water molecule will not take an electron with it making it a hydrogen ion(1- Charge), forming a hydronium ion (H3O^+) and a hydroxide ion (OH-)

6. What defines an acid and a base? An acid is a substance that increases the hydrogen ion concentration of a solution. A base is a substance that reduces the hydrogen ion concentration of a solution.

7. Why are “apparently” small changes in pH so important in biology? Because the changes can have so many effects on chemical reactions on certain molecules and the pH level helps to determine whether or not the cell is harmful.

8. What is a buffer and write and explain the carbonic acid buffer system in human blood – yes we are back to the equation AGAIN! A buffer is a substance that helps maintain a certain pH level in certain cells. It minimizes changes in concentration of H+ and OH- ions in a solution. The carbonic acid buffer system takes hydrogen ions from a solution when in excess and donates them to a solution that has been depleted of them.

9. What is acid precipitation and why is it important to living organisms?
 * It is rain, snow or fog that has a pH lower or more acidic than pH 5.6. It can damage life in lakes or streams. This can also affect nutrition needed for plant growth. Also, acid precipitation can affect soil, in which forests survive from. **