1. Chapter 3 Water

2. 1. Overview

3. H2OH2O Exists as a solid, liquid, or vapor required by living things cells surrounded by water cells 70-90% water Earth is ~75% water

4. 2. Polar Polar: opposite ends of molecule have different charges Oxygen more electronegative than Hydrogen Oxygen has partial negative charge; electrons are pulled toward it Hydrogen: partial positive charge

5. What is electronegativity? How does it affect interactions between water molecules? one atom’s attraction for electrons in covalent bond. O more electronegative than H O has a partial (-) charge and H (+) Atoms with opposite charges are attracted to polar H 2 O molecules forming Hydrogen bonds

6. 3. Hydrogen Bonding (+) charge on hydrogen of H 2 O is attracted to the (-) charge on the oxygen of another H 2 O molecule forms weak hydrogen bond each water molecule can form up to 4 H-bonds Hydrogen bonds + + H H + +  – –  – –  – –  – –

7. 4. Emergent properties of water that provide stability for life.

8. Cohesion: H 2 O molecules stick together; H – bonds allows water & nutrient transport in plants from roots to leaves; against gravity H 2 O “pulls” up when it evaporates through the leaves of a plant What is this evaporation called?

9. 4. Emergent properties of water that provide stability for life. Surface Tension: “thin skin” that forms on water Water has higher surface tension than other liquids Invisible film Related to cohesion Many animals walk or run on water

10. 4. Emergent properties of water that provide stability for life. Adhesion: clinging of one substance to another Water sticks to cell walls in plants Water sticks to glass, forms meniscus Capillary Action: water is drawn up against the pull of gravity Related to cohesion & adhesion

12. 4. Emergent properties of water that provide stability for life. Water moderates temperature Specific Heat: amount of energy that must be absorbed or lost to change 1g by 1 o C Water has high specific heat compared to other substances (1calorie per 1gram per 1 o C) Absorbs heat from the air when it is hot, and releases heat into the air it is cold out Requires lots of energy to make the temp of water change, because MANY H - bonds must be broken Water minimizes temp. fluctuations Sweating, release of water from plants cools terrestrial organisms

13. 4. Emergent properties of water that provide stability for life. Vaporization: evaporation Transformation of liquid to a gas Molecules move fast enough to “escape” liquid Heating liquid = faster molecule movement Heat of vaporization = amount of heat liquid must absorb for 1g to change from liquid to gas Evaporative Cooling: As water turns to gas and evaporates, heat is taken with it, what’s left behind is cooled

14. Explain the saying, “It’s not the heat; it’s the humidity.” High humidity hampers cooling by suppressing the evaporation of sweat.

15. 4. Emergent properties of water that provide stability for life. Density of H 2 O Ice less dense than water; expands when below 4 O C Oceans & lakes don’t freeze because ice floats and insulates life below

16. Ice Hydrogen bonds are stable Liquid water Hydrogen bonds break and re-form Hydrogen bond

17. 4. Emergent properties of water that provide stability for life. Water is the universal solvent.

18. 4. Emergent properties of water that provide stability for life. Water, the solvent of life: dissolves substances  aqueous solutions dissolves ionic & polar substances salt water Water: solvent: does the dissolving NaCl: solute: gets dissolved Hydrophilic: “water loving” Ionic bonds or polar molecules Hydrophobic: “water fearing” Covalent bonds & non-polar molecules

19. 5. Dissociation  Acids + Bases hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other: H 2 O  H + (H 3 O + ) + OH - Increase in H + = acid Increase in OH - = base (decrease in H + ) H H H H H H H H O O OO 2H 2 OHydronium ion (H 3 O + ) Hydroxide ion (OH – )

20. Calculate How many grams of lactic acid (C 3 H 6 O 3) are in 1 liter of a 0.5M solution of lactic acid? 45 grams

21. 6. pH acidic0-6.999 – acidic neutral7 - neutral basic7.0001-14 – basic Living cells require an internal pH ~ 7 pH = - log [H+] [H+] = 10 –4  pH = 4

22. 7. Buffers Maintain pH of a solution in the presence of an acid or base. Blood = pH 7.4 Bicarbonate buffer is found in blood plasma Organisms use buffers to maintain homeostasis Accept H+ when they are in excess Donate H+ when they are depleted

23. Calculate The carbonic acid/bicarbonate system is an important biological buffer. Label the molecule and ions in this equation, and indicate which is the H + donor and which is the acceptor. H 2 CO 3  HCO 3 - + H + In which direction will this reaction proceed a)when the pH of the solution falls? b)when the pH of the solution rises above normal level? carbonic acid bicarbonate hydrogen ion H + donor H + acceptor a)To the left, bicarbonate acts as a base b)To the right, carbonic acid donates H +

24. CO 2 CO 2 + H 2 OH 2 CO 3 H + + CO 3 2  H + + HCO 3  HCO 3  CO 3 2  +Ca 2+ CaCO 3 CO 2 reacts with water in the ocean to form carbonic acid (H 2 CO 3 ) Carbonic acid dissociates into H+ ions and bicarbonate ions HCO 3 - The added H+ combines with carbonate ions (CO 3 2- ) forming more HCO 3 - Less CO 3 2- is available for formation of CaCO 3 by marine organisms. Ocean Acidification

25. Explain how increasing amounts of CO 2 dissolving in the ocean leads to ocean acidification. How does this change in pH affect carbonate ion concentration and the rate of calcification? CO 2 reacts with H 2 O to form carbonic acid H 2 CO 3 which dissociates into H + and bicarbonate HCO 3 -. Although the carbonic acid – bicarbonate reaction is a buffering system, adding CO 2 drives the reaction to the right, releasing more H + and lowering the pH. The excess protons combine with CO 3 2- to form bicarbonate, lowering the amount of carbonate available for the formation of CaCO 3 by corals.

27. Water Transport in Plants StructureFunction Roots Root hairs Waxy barrier in the root Xylem Small pores in the leaves: stomata

29. Water Transport in Plants What is transpiration? What is the difference between adhesion and cohesion? Give examples of each in water transport. What is the transpiration-cohesion-surface tension mechanism? How does this mechanism explain how water and soil nutrients move from the roots of a plant to its leaves?