10/8/14 Objective: What are the properties of water? Do Now: Take out your HW Chapter 4: The Chemical Basis of Life

Polar Molecule: -A molecule in which opposite ends have opposite electric charges -Oxygen end of the molecule has a slight negative charge, while 2 Hydrogen atoms have a slightly positive charge

Hydrogen Bond - Hydrogen Bond: -The slightly negative oxygen end attracts slightly positive hydrogen end of other water molecules

Where does water enter this tree? Where does evaporation of water occur? How does water travel 300 feet against the forces of gravity?

Cohesion: -Tendency of molecules of the same kind to stick to one another Adhesion: -Attraction between unlike molecules -Adhesion between water molecules and walls of tubes in tree resist pull of gravity.

Surface Tension: water molecules “stick” together

2. Temperature Moderation energy associated with the random movement of atoms in a sample of matter Think: when molecules are moving fast, what effect does it have? Thermal Energy Temperature: measure of the average energy of random motion of the particles in a substance Heating=breaks H bonds Cooling= forms H bonds

Think: Pasta in a pot. Turn on the burner. After 2 minutes, can you touch the pot? Can you stick your finger in the water? Why? Water has H bonds, but pot does not, all of initial heat-energy goes to breaking H bonds, once broken then the water molecules can start moving to heat up.

Water has a high specific heat (amount of heat needed to raise temp 1 degree Celsius) Water takes a long time to heat up/cool down so it is much more steady than the temperature of air.

Water has a high specific heat- important for life Specific heat: amount of heat a substance needs for a given increase in temperature. (H-bonding restricts movement) –takes a lot to heat it up and retains heat longer than surroundings, must break h-bonds –takes a lot to cool it down H 2 O moderates temperatures on Earth

Why does this lake not freeze from bottom up, but only at the top?

Hydrogen bonds in water Hydrogen bonds in ice

3. Low Density of Ice density: amount of matter in a given volume Ice is less dense than liquid water WHY? Hydrogen bonds keep molecules spaced evenly making ice less dense than water (producing a crystal lattice)

4. Dissolve Substances solution: uniform mixture of two or more substances –Salt water solvent: the substance that dissolves the other substance (ex: water) solute: the substance being dissolved (salt) –aqueous solution (aq): water is the solvent

5. Acids, Bases, and pH In some aqueous solutions, some water molecules break into ions –H + and OH - acid: a compound that donates H + to a solution –HCl = H + and Cl - base: a compound that removes H + ions pH scale: describes how acidic or basic a solution is –0 = most acidic –7 = neutral (pure water) –14 = most basic buffers: substances that cause a solution to resist changes in pH –Blood pH