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WATER & pH. 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.
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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
Water transport in plants COHESION & ADHESION
Walking on water HIGH SURFACE TENSION: RESULT OF H-BONDS
The structure of ice ICE FLOATS BECAUSE IT IS LESS DENSE
Ice, water, and steam Ice Water Steam WATER IS MOST DENSE AT 4 DEGREES C
A crystal of table salt dissolving in water WATER DISSOLVES POLAR AND CHARGED MOLECULES
Dissociation • Dissociation of water: • H2O H+ + OH- • Dissociation of other things: • Ex: HCl H+ + Cl- • Acids yield H+ions • Bases yield OH- ions
pH • Aqueous solutions @ 25o C • [H+][OH-] = 10-14 • [ ] = molar concentration • pH = -log [H+] • pOH = -log [OH-] • Ex: neutral solution, [H+] = 10-7 • pH = -log [10-7] = -(-7) = 7
Buffers • Minimize changes in pH • Accepts H+ in excess • donates H+ when depleted • Weak acid and corresponding base • Example: • H2CO3 HCO3- + H+ Rise in pH 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 membrane
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? • Water’s change in density when it condenses • Water’s ability to dissolve molecules in the air • The release of heat by the formation of hydrogen bonds • The absorption of heat by the breaking of hydrogen bonds • Water’s high surface tension
Question 2 The bonds that are broken when water vaporizes are • Ionic bonds • Bonds between water molecules • Bonds between atoms within individual water molecules • Polar covalent bonds • Nonpolar covalent bonds
Question 3 Which of the following is an example of a hydrophobic material? • Paper • Table salt • Wax • Sugar • 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? • 4.0 M • 10-10 M • 10-4 M • 104 M • 4%
Question 5 What is the hydroxide ion concentration of the lake described above? • 10-7 M • 10-4 M • 10-10 M • 10-14 M • 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