Period+2+Chem+ch+3


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

1. Why is water considered a polar molecule? It has two hydrogen to the oxygen atom by single covalent bonds. Oxygen is more electronegative than hydrogen, the electrons of the polar bonds spend more time closer to the oxygen atom.

beal. . . OK, period 3 has a better explanation.

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
 * Cohesion is the binding together of like molecules, often by hydrogen bonds. Negative oxygen in one water molecule binds cohesively to the positive hydrogen of another. Water droplets are held together by cohesive forces. Another example is water traveling up the root systems of plants. **

beal. . . good!

b. Adhesion
 * Adhesion is the attraction between differenct kinds of molecules. The polarity of water allows the negative oxygen to be attracted to positive ions and the positive hydrogen to be attracted to negative ions. Adhesion helps water resist the downward pull of gravity and travel up the root systems of plants. **

beal. . . hmm. . . you used this example twice. . . how can it be both and why?

c. Surface tension **Surface tension is a measure of how difficult it is to stretch or break the surface of a liquid. Water has surface tension because of the hydrogen bonding of surface molcules and hydrogen bonds happen because of the polarity. Many insects can walk across water because of surface tension.**

beal. . . good!

d. High specific heat
 * Specific heat is defined as the amount of heat that must be absorbed or lost for one gram of that substance to change its temp by 1 degree Celsius. The high specific heat of water is because of hydrogen bonding. Heat must be absorbed for hydrogen bonds to break and heat is released when hydrogen bonds form. A calorie of heat causes a relatively small change in temperature of water because a lot of the heat is used to disrupt hydrogen bonds before the molcules can begin moving faster. When the temperature drops slightly it creates more hydrogen bonds and releases a considerable amount of heat. Because organisms are made mostly of water, they are more able to resist changes in their own temperatures than if they were made of a liquid with a lower specific heat. **

beal. . . good!

e. Heat of vaporization
 * Heat of vaporization is the quantity of heat a liquid must absorb for one gram of it to be converted from a liquid to a gas. For the same reason that water has a high specific heat, it also has a high heat of evaporization. Water's high heat of vaporization helps to moderate the Earth's climate. Solar heat absorbed by tropical seas is consumed during the evaporation of surface water. **

f. Evaporative cooling beal. . . good!
 * Evaporative cooling is the property of a liquid wherby the surface becomes cooler during evaporization, owing to a loss of highly kinetic molcules to the gaseous state. For this to happen, the hydrogen bonds that occur because of water's polarity have to be broken, which requires heat energy. An example is how humans sweat. **

3. What is special about water and density?
 * Water is abnormally more dense as a liquid than it is a solid. **

beal. . . good!

4. Define the following terms: a. Solute- a substance that is dissolved in a solution. For example, in hot chocolate the chocolate mix is the solute.

beal. . . good!

b. Solvent- The dissolving agent of a solution.Water is the most versatile solvent known. For exaple in hot chocolate mix the water is the solvent.

beal. . . good!

c. Aqueous solution- A solution in which water is the solvent.

beal. . . good!

d. Hydrophilic- Having an affinity for water.

beal. . . good!

e. Hydrophobic- Having an aversion to water; tending to coalesce and form droplets in water.

beal. . . good!

f. Colloid- A mixture made up of a liquid and particles that (because of thier large size) remain suspended in that liquid.

beal. . . good!

g. Hydration shell- The sphere of water molecules around each dissolved ion.

beal. . . good!

h. Molarity- A common measure of solute concentration, referring to the number of moles of solute per liter of solution.

beal. . . good!

5. Label the diagram below to demonstrate the dissociation of the water molecule and then relate this diagram to pH. H2O + H2O > H30+ + OH- White = Hydrogen Red = Oxygen

Concentrations of H+ and OH- are equal in pure water until an acid or base is added. pH determines how acidic or basic a solution is. A high concentration of H+ will result in an acidic solution with a pH less that seven, while a high concentration of OH- molecules will result in a basic solution with a pH greater than seven.

beal. . . good!

6. What defines an acid and a base? **it is the dissociation of water molecules. acids are a substance that increase the hydrogen ion concentration of solution. It has more h+ than OH-. Bases reduce H+ concentration. If something is from 6-0 on the pH scale it is acidic. It is a base if it is from 8-14 on the pH scale.**



beal. . . good!

7. Why are “apparently” small changes in pH so important in biology? ** because chemical processes of the cell are very sensitive to the concentrations of hydrogen and hyroxide ions. Also, the changes can have so many effects on chemical reactions on certain molecules. ** media type="youtube" key="KTox9wu07JM" height="344" width="425"

beal. . . good! weird video.

8. What is a buffer and write and explain the carbonic acid buffer system in human blood. **__Buffer__: substances that minimize changes in the concentrations of H+ and OH- in a solution (Or help maintain the pH). If there is too many hydrogen ions, the buffer takes or accepts some hydrogen ions. When there is too few hydrogen ions, the buffer donates some.** Human blood needs to remain neutral so maintaining a constant pH is very important. An example of a buffer for human blood is:

// ((Note that the "donor" is an acid, and the "taker (or acceptor)" is a base)) //

If pH begins to rise (H+ concentration decreases) the formula goes from left to right and the carbonic acid dissociates and releases hydrogen ions. If the pH begins to fall (H+ concentration increases) the formula goes from right to left and HCO3- removes the hydrogen ion and becomes H2CO3.

beal. . . good!

9. What is acid precipitation and why is it important to living organisms?

It is rain, snow or fog with a ph lower or more acidic ph 5.6, it is the most important environmental problems that an environment can face. The aicd rain pollutes every part of the environment and slows the growth of everything, eventually leading to injuries or deaths among the environment. The water becomes to acidiic to be used and the fish that live in it die, and the species that depend on it also slowly start to die off. It also harms the trees, it seeps into the the tree. Instead of the water turning from gas into water, it remains in the gas form and kills the trees.

beal. . . good!