Chapter 3 Notes Water and the Fitness of the Environment

Concept 3.1 Water is a polar molecule, opposite ends have opposite charges. A slightly positive hydrogen is attracted to a slightly negative oxygen of a nearby molecule. The two molecules are held together by a hydrogen bond

Concept 3.1 Hydrogen bond  – – H  + + H O — —  + +  + +  + +  – –  – –  – –

Concept 3.2 Water will stick to each other with hydrogen bonds (1/20 th as strong as covalent bonds). Results of Hydrogen bonds 1) Cohesion: when a substance (water) is held together by hydrogen bonds 2) Adhesion: the clinging of one substance to another

Concept 3.2 Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement

Concept 3.2 3) Surface tension: measure of how difficult it is to stretch or break the surface of a liquid. - arrangement of hydrogen bonds between water molecules on surface and below

Concept 3.2

4) Water stabilizes temperatures because of its high specific heat. Specific heat: amt. of heat that must be absorbed or lost for 1g of a substance to change its temp. by 1 o C. - ex. hot pot of warm water

Concept 3.2 San Diego 72° 40 miles Pacific Ocean 70s (°F ) 80s 90s 100s Santa Barbara 73° Los Angeles (Airport) 75° Burbank 90° San Bernardino 100° Riverside 96° Santa Ana 84° Palm Springs 106°

Concept 3.2 Kinetic energy: energy of motion. Atoms have kinetic energy because they are always moving. Heat: measure of the total quantity of kinetic energy due to molecular motion. Temperature: intensity of heat due to the average kinetic energy of the molecules

Concept 3.2 Celsius scale( o C): water freezes at 0 o C and boils at 100 o C. Calorie (cal): the amount of heat energy it takes to raise the temp. of 1g of water by 1 o C. Kilocalorie (kcal): 1 “food” calorie Joule (J): another unit of energy. 1 J = cal; 1 cal = J

Concept 3.2 Molecules of a liquid will stay together because of attraction. If they move fast enough they will overcome the attraction and can enter the air as gas. Heat of vaporization: quantity of heat a liquid must absorb for 1g of it to be converted to gas

Concept 3.2 5) Water is the solvent of life. Solution: homogeneous mixture of two or more substances Solvent (dissolving agent) + solute (substance that is dissolved) = solution Aqueous solution: water is the solvent

Concept 3.2 Cl – Na + Cl – – – – – – – – – Na + – – – +

Hydration shell: sphere of water molecules around each dissolved ion Hydrophilic (hydro=water, philios=love): any substance that has an affinity to water. ionic or polar molecules Hydrophobic (phobos=fearing): any substance that repels water. Nonpolar or non-ionic Concept 3.2

(c) Ionic and polar regions on the protein’s surface attract water molecules. (b) Lysozyme molecule (purple) in an aqueous environment

Concept 3.2 Mole (mol): molecular weight of a substance Molarity: number of moles of solute per liter of solution

Concept 3.3 A hydrogen atom shared by two water molecules in a hydrogen bond can shift from one molecule to another. Hydrogen ion (H + ), charge is +1 Hydroxide ion (OH - ), charge is -1 The proton binds to another water molecule making H 3 O +.

Concept 3.3 Hydronium ion (H 3 O + ) Hydroxide ion (OH – ) 2H 2 O H H H H H H H H O O O O

Concept 3.3 Acid: substance that increases the [H + ] of a sln. - ex. HCl -> H + + Cl - Base: substance that reduces the [H + ] of a sln. Also, increase the [OH - ]. - ex. NH 3 + H + -> NH 4 + NaOH -> Na + + OH -

Concept 3.3 The pH of a sln. is the negative logarithm of the [H + ] - pH = -log[H + ] - neutral sln. [H + ] is log = -(-7)= 7 - If acid is added and [H + ] is 10 -5, the [OH - ] is

Concept 3.3

More acidic 0 Acid rain Normal rain More basic

Buffers: substances that minimize changes in the concentration of H + and OH - in a sln. - buffers accept H + from a sln. when they are in excess and donate H + when they have been depleted. - use of carbonic acid in blood Concept 3.3