Fun Facts• 50-95% of weight of living things• Only common substance that exists in solid, liquid and gas forms• If earth was smooth, depth of water would be 2.5m• 98% of water is in liquid form – 2% polar, glacial, soil, atmosphere, organisms – Most evaporation is from oceans
Special Properties• Cohesion/ Adhesion• High surface tension• High specific heat – required to heat 1g of water 1 degree C• High boiling point• High heat of vaporization – Heat required to convert 1 g of water to water vapor – 580 cal• Ice floats• Versatile Solvent
Buffers• Minimize changes in pH – Accepts H+ in excess – donates H+ when depleted• Weak acid and corresponding base• Example: Rise in pH• H2CO3 HCO3- + H+ Drop in pH
Water Movement• Water potential – – Potential energy of water molecules • gravity, pressure, conc. of solutes, etc. – Movement from a region of greater potential to a region of lower water potential• Osmotic potential – – Movement across a selectively permeable membrane – Determined by measuring the pressure required to stop the osmotic movement of water in the solution
Water Movement Water moves across a selectively permeable membraneFrom a region of: To a region of:Higher water potential Lower water potentialLower solute conc. Higher solute conc.Hypotonic soln. (less Hypertonic soln. (moresolute) solute)Lower osmotic potential Higher osmotic potential
Question 1 Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability of sweat to lower body temperature?A. Water’s change in density when it condensesB. Water’s ability to dissolve molecules in the airC. The release of heat by the formation of hydrogen bondsD. The absorption of heat by the breaking of hydrogen bondsE. Water’s high surface tension
Question 2 The bonds that are broken when water vaporizes areA. Ionic bondsB. Bonds between water moleculesC. Bonds between atoms within individual water moleculesD. Polar covalent bondsE. Nonpolar covalent bonds
Question 3 Which of the following is an example of a hydrophobic material?A. PaperB. Table saltC. WaxD. SugarE. Pasta
Question 4 Acid precipitation has lowered the pH of a particular lake to 4.0. What is the hydrogen ion concentration of the lake?A. 4.0 MB. 10-10 MC. 10-4 MD. 104 ME. 4%
Question 5 What is the hydroxide ion concentration of the lake described above?A. 10-7 MB. 10-4 MC. 10-10 MD. 10-14 ME. 10 M
Summary• Polarity of water results in H-bonding – Water’s special properties• Organisms depend on cohesion of water – Pull water up plant vessels – Surface tension• Water moderates temperatures on earth – High specific heat – Evaporative cooling/ high heat of vaporization• Ice floats – Lakes and oceans don’t freeze, life goes on under ice• Water is the solvent of life – Dissolves charged/ polar substances
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