WATER’S POLARITY and ITS EFFECTS

1. WATER’S POLARITY and ITS EFFECTS

2. PROPERTIES of WATER • 4 valence electrons • Polar molecule • Cohesive behavior • Resists changes in temperature • High heat of vaporization and cools surfaces as it evaporates • Expands when freezes • Universal solvent

3. WATER MOLECULE • Water as a Polar Molecule • Oxygen more electronegative– slightly more (-). • Hydrogen less electronegative– slightly more (+) H+ H+ O-

4. HYDROGEN ATTRACTIONS • Weak attractions between polar ends of different molecules (H+ and O-) like in water • Causes cohesion and adhesion. • NOT A “BOND”

5. COHESION vs. ADHESION • Cohesion – attraction between molecules of the same substance. • i.e. water droplets – “beads up” • Adhesion – attraction between molecules of different substances. • i.e. surface tension – allows for bugs to “walk” on water

6. Figure 3.1 Hydrogen bonds between water molecules 

7. Figure 3.5 The structure of ice (Layer 2)

8. Molecules continuously move

9. Figure 3.3 Walking on water

12. Figure 3.7 A crystal of table salt dissolving in water

13. Like dissolves like!!!!

14. MIXTURES • Two or more elements or compounds that are physically mixed – not chemically mixed. • i.e. salt/pepper, iced tea • Water can form 2 types of mixtures: • Solutions - homogenous • Suspensions - heterogeneous

15. SOLUTION • Homogenous mixture in which molecules are evenly distributed • Solute – substance being dissolved • Solvent – substance doing the dissolving. Cl- Cl- Na+ Na+ Water Water

16. SUSPENSION • Heterogeneous mixture in which materials are not dissolved in water and separate or settle out. • i.e. blood, salad dressing, snow globe

17. DISSOCIATION of WATER • Occasionally, a hydrogen atom is transferred between water molecules that are hydrogen attracted together • H+ (a proton) is transferred • Transferred H+ to a water molecule creates hydronium (H3O+) • Water that lost H+ has a net negative charge and is called a hydroxide ion (OH-) • Ionization of H2O is expressed as the dissociation into H+ and OH- • Reaction is reversible

18. pH • Negative log of the [H+] expressed in moles/L • Water molecules can react and break apart to form ions (H+ and OH-) • pH Scale – used to measure degree of acidity • 0-7 = acids (form H+ ions in water) • 7 = neutral ([H+] ions = [OH-] ions) • 7-14 = bases (form OH- ions in water) • [brackets] represents concentration

19. USEFUL pH EQUATIONS • [H+][OH-] = 10-14 • pH = -log [H+] • -log 10-7 = -(-7) = 7

20. ACIDS • Increase [H+] in solution • H+ donors • i.e. HCl H+ + Cl- • [H+] > [OH-] is acidic • i.e. [H+] = 10-5 M and [OH-] = 10-9 M

21. BASES • Decreases [H+] in solution • H+ acceptors • i.e. NH3 + H+↔ NH4+ • Increases [OH-] by dissociating into ions • i.e. NaOH ↔ Na+ + OH- • [H+] < [OH-] is basic • i.e. [H+] = 10-11 M and [OH-] = 10--3 M

22. NEUTRALS • [H+] = [OH-] is neutral • i.e. [H+] = 107 M and [OH-] = 10-7 M

23. pH SCALE Oven cleaner Bleach Ammonia Solution Oven cleaner Oven cleaner Bleach Bleach Increasing bases Soap Ammonia solution Ammonia solution Increasingly Basic Soap Soap Sea water Sea water Sea water Human Blood Neutral Pure water Human blood Pure water Milk Pure water Milk Normal rainfall Normal rainfall Acid rain Acid Rain Tomato juice Increasing acids Tomato Juice Lemon juice Lemon Juice Stomach acid Stomach Acid

24. WHAT are BUFFERS? • Weak acids/bases that minimize huge fluctuations in pH • It works by accepting H+ from solution when they are in excess • OR by donating H+ to solution if depleted • Help organisms maintain the pH of body fluids within a pH range (usually 6-8)

25. EXAMPLE of BUFFERS • i.e. carbonic acid regulates the pH of blood • pH of blood 7.4 • Blood pH is bad at 7 or 7.8; a person can only survive a few minutes if it fluctuates this low or high • H2CO3↔ HCO3- + H+ • Carbonic acid can yield biocarbonate and a proton (& vice versa)

26. Things in Chemistry you need for AP Biology (or read in your text) • Kinetics • Thermodynamics • Kcal, cal, and joules • Specific Heat • Heat of vaporization