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Chemistry of Life Properties of Water
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POGIL Use your “seed planting groups” Select a:
MANAGER READER 1st and last name (or initial) on sticky note
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Why are we studying water?
More about Water Why are we studying water? All life occurs in water inside & outside the cell
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Chemistry of water H2O molecules form H-bonds with each other
+H attracted to –O creates a sticky molecule APBio/TOPICS/Biochemistry/Movies AP/hydrogenbonds-Thinkwell.swf
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Polarity of H2O O- will bond with H+ on a different molecule of H2O = hydrogen bond H2O can form up to 4 bonds
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Elixir of Life Special properties of water 1. cohesion & adhesion
surface tension, capillary action 2. good solvent many molecules dissolve in H2O hydrophilic vs. hydrophobic 3. lower density as a solid ice floats! 4. high specific heat water stores heat 5. high heat of vaporization heats & cools slowly Ice! I could use more ice!
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Try that with flour… or sugar…
1. Cohesion & Adhesion Cohesion H bonding between “like” molecules water is “sticky” Ex: drinking straw surface tension = measure of how difficult it is to break or stretch surface of liquid Ex: Water strider Try that with flour… or sugar… Cohesion H bonding between H2O molecules water is “sticky” surface tension capillary action drinking straw Adhesion H bonding between H2O & other substances meniscus water climbs up paper towel or cloth
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1. Cohesion & Adhesion Adhesion
H bonding between “unlike” molecules (H2O & other substances) capillary action - Adhesion of H2O to vessel walls counters ↓ pull of gravity Ex: meniscus Ex: water climbs up paper towel or cloth Cohesion H bonding between H2O molecules water is “sticky” surface tension capillary action drinking straw Adhesion H bonding between H2O & other substances meniscus water climbs up paper towel or cloth
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How does H2O get to top of trees?
Transpiration is built on cohesion & adhesion APBio/TOPICS/04Biochemistry/MoviesAP/03_03WaterTransport_A.swf
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H2O clings to each other by cohesion; cling to xylem tubes by adhesion
Transpiration = movement of H2O up plants H2O clings to each other by cohesion; cling to xylem tubes by adhesion
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2. Water is the Solvent of Life
Solution = liquid, homogeneous mixture of 2+ substances Solvent = dissolving agent (liquid) Solute = dissolved substance Water = versatile solvent
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2. Water is the solvent of life
Polarity makes H2O a good solvent polar H2O molecules surround + & – ions solvents dissolve solutes creating solutions 2. Water is a good solvent = the solvent of life Polarity makes H2O a good solvent polar H2O molecules surround + & – ions solvents dissolve solutes creating solutions What dissolves in water easily? polar or non-polar molecules? How about oxygen -- does that dissolve in H2O?
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What dissolves in water?
Hydrophilic substances have attraction to H2O “like” water polar or non-polar? Hydrophilic substances have attraction to H2O
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What doesn’t dissolve in water?
Hydrophobic substances that don’t have an attraction to H2O polar or non-polar? Oh, look hydrocarbons! Hydrophobic substances that don’t have an attraction to H2O fat (triglycerol)
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And this has made all the difference!
3. The special case of ice Most (all?) substances are more dense when they are solid, but not water… Ice floats! H bonds form a crystal Ice! I could use more ice! Most (all?) substances are more dense when they are solid, but not water… Lower density as a solid = Ice floats! H bonds form a crystal And this has made all the difference!
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Why is “ice floats” important?
Oceans & lakes don’t freeze solid surface ice insulates water below allowing life to survive the winter if ice sank… ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw Oceans & lakes don’t freeze solid surface ice insulates water below allowing life to survive the winter if ice sank… ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw seasonal turnover of lakes sinking cold H2O cycles nutrients in autumn
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Floating Ice is important…
seasonal turnover of lakes sinking cold H2O cycles nutrients in autumn Ice = solid habitat (polar bears)
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Specific heat & climate
H2O resists changes in temperature high specific heat takes a lot to heat it up takes a lot to cool it down H2O moderates temperatures on Earth Specific heat H2O resists changes in temperature high specific heat = heats & cools slowly takes a lot to heat it up takes a lot to cool it down H2O moderates temperatures on Earth Specific heat & climate
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Water’s high specific heat is important
Change temp less when absorbs/loses heat Large bodies of water absorb and store more heat warmer coastal areas Create stable marine/land environment Humans ~65% H2O stable temp, resist temp. change
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5. High Heat of Vaporization
is the amount of energy (enthalpy) that must be added to a liquid substance, to transform a quantity of that substance into a gas
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High Heat of Vaporization is important because it provides…
Evaporative Cooling Water has high heat of vaporization Molecules with greatest KE leave as gas Stable temp in lakes & ponds Cool plants Human sweat
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5. Heat of vaporization Evaporative cooling
Organisms rely on heat of vaporization to remove body heat
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Ionization of water & pH
Water ionizes H+ splits off from H2O, leaving OH– if [H+] = [-OH], water is neutral if [H+] > [-OH], water is acidic if [H+] < [-OH], water is basic pH scale how acid or basic solution is 0 7 14 Water ionizes H+ splits off from H2O, leaving OH– H2O H+ + OH– if [H+] = [-OH], water is neutral if [H+] > [-OH], water is acidic if [H+] < [-OH], water is basic pH scale how acid or basic solution is 1 7 14 H2O H+ + OH–
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pH Scale The pH scale runs between 0 and 14 and measures the relative acidity and alkalinity of aqueous solutions. Acids have an excess of H+ ions, and a pH below 7.0. Bases have an excess of OH- ions, and a pH above 7.0
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Acids and Bases H2O H+ + OH-
(gains proton) H+ + H2O H3O+ (hydronium ion) (loses proton) H2O – H+ OH- (hydroxide ion)
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7 14 Basic Acidic Acids and Bases pH Scale
Acid = increases H+ concentration (HCl) [H+] > [OH-] Base = reduces H+ concentration (NaOH) [H+] < [OH-] Most biological fluids are pH 6-8 7 14 Basic Acidic pH Scale
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Figure 3.10 The pH scale and pH values of some aqueous solutions
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tenfold change in H+ ions
10–1 H+ Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 100 Hydrochloric acid 10–2 2 10–3 Vinegar, cola, beer 3 10–4 Tomatoes 4 10–5 Black coffee, Rainwater 5 10–6 Urine, Saliva 6 10–7 Pure water, Blood 7 10–8 Seawater 8 10–9 Baking soda 9 10–10 Great Salt Lake 10 10–11 Household ammonia 11 10–12 Household bleach 12 10–13 Oven cleaner 13 10–14 Sodium hydroxide 14 pH Scale tenfold change in H+ ions pH1 pH2 10-1 10-2 10 times less H+ pH8 pH7 10-8 10-7 10 times more H+ pH10 pH8 10-10 10-8 100 times more H+ In pure water only 1 water molecule in every 554 million is dissociated tenfold change in H+ ions pH1 pH2 10-1 10-2 10 times less H+ pH8 pH7 10-8 10-7 10 times more H+ pH10 pH8 10-10 10-8 100 times more H+
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Buffers & cellular regulation
pH of cells must be kept ~7 pH affects shape of molecules shape of molecules affect function therefore pH affects cellular function Control pH by buffers reservoir of H+ donate H+ when [H+] falls absorb H+ when [H+] rises Buffers resist big changes in pH 1 2 3 4 5 6 7 8 9 Amount of base added Buffering range pH Exercise = acidic in muscles CO2 = carbonic acid lactic acid body uses buffers to counter act this
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Ocean acidification threatens coral reef ecosystems
CO2 mixed with seawater Carbonic acid (lowers ocean pH)
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The effects of acid precipitation on a forest
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Examples of Benefits to Life
H2O Property Chemical Explanation Examples of Benefits to Life Cohesion polar H-bond like-like ↑gravity plants, trees Adhesion unlike-unlike plants xylem bloodveins Surface Tension diff. in stretch break surface bugswater Specific Heat Absorbs & retains E oceanmod temp protect marine life Evaporation liquidgas KE Cooling Homeostasis Universal Substance Polarityionic Good dissolver solvent
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Any Questions? Do one brave thing today…then run like hell!
He’s gonna earn a Darwin Award! Any Questions? Do one brave thing today…then run like hell!
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Ice Fishing in Barrow, Alaska
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More Chemistry Support
Chemtutor.com Chemspider.com Chemistry.about.com Bozeman Science
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Bozeman Science Water - A Polar Molecule
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Lab: Properties of Water
Rotate through 12 stations (1A, 1B, 2A, 2B, etc) Formal Lab Grade Answer station-specific questions at each station during class. Summaries should be written at home!!!
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