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Published byLetitia Hilary Rodgers Modified over 8 years ago
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Water- A Necessity to Life Chapter 3 – Campbell Reece Tamara Lookabaugh Moore High School AP Biology Lecture
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Structure of Water Where are the electrons? What kind of bond is this molecule making? What kind of bonding does is make with other water molecules? H H Oxygen
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Water is the solvent of life Polarity makes H 2 O a good solvent –polar H 2 O molecules surround + & – ions –solvents dissolve solutes creating solutions
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How does H 2 O get to top of trees? Transpiration built on cohesion & adhesion
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Water Polar~ opposite ends, opposite charges Cohesion~ H+ bonds holding molecules together Adhesion~ H+ bonds holding molecules to another substance Surface tension~ measurement of the difficulty to break or stretch the surface of a liquid Specific heat~ amount of heat absorbed or lost to change temperature by 1oC Heat of vaporization~ quantity of heat required to convert 1g from liquid to gas states Density……….
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Density Less dense as solid than liquid Due to hydrogen bonding Crystalline lattice keeps molecules at a distance
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Acid/Base & pH Dissociation of water into a hydrogen ion and a hydroxide ion Acid: increases the hydrogen concentration of a solution Base: reduces the hydrogen ion concentration of a solution pH: “power of hydrogen” Buffers: substances that minimize H+ and OH- concentrations (accepts or donates H+ ions)
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Do you dissolve in water? Hydrophilic –substances have attraction to H 2 O –polar or non-polar?
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Or don’t you? Hydrophobic –substances that don’t have an attraction to H 2 O –polar or non-polar? fat (triglycerol)
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Water as a Floating Solid is Unique Most (all?) substances are more dense when they are solid, but Not water… Ice floats! –H bonds form a crystal that actually expands –Think about how water freezes –What does it look like in an ice tray?
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Ice floats
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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 –seasonal turnover of lakes cycles nutrients in autumn
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Specific heat H 2 O resists changes in temperature –high specific heat –takes a lot to heat it up –takes a lot to cool it down H 2 O moderates temperatures on Earth
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Specific heat & climate
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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 H 2 O, 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 –1 7 14 H 2 O H + + OH –
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pH Scale 10 –1 H + Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 10 0 Hydrochloric acid0 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 hydroxide14
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10 0 1 2 3 4 5 6 7 8 9 3 Amount of base added Buffering range 452 pH Buffers & cellular regulation pH of cells must be kept ~7 –pH affects shape of molecules –shape of molecules affect function –pH affects cellular function Control pH by buffers –reservoir of H + donate H+ when [H + ] falls absorb H+ when [H + ] rises
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