WATER & pH

1. WATER & pH

2. 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

3. 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

4. Hydrogen bonds between water molecules 

5. Water transport in plants COHESION & ADHESION

6. Walking on water HIGH SURFACE TENSION: RESULT OF H-BONDS

7. Evaporative cooling

8. The structure of ice

9. The structure of ice ICE FLOATS BECAUSE IT IS LESS DENSE

10. Ice, water, and steam Ice Water Steam WATER IS MOST DENSE AT 4 DEGREES C

11. Ice floats and frozen benzene sinks

12. Floating ice and the fitness of the environment

13. A crystal of table salt dissolving in water WATER DISSOLVES POLAR AND CHARGED MOLECULES

14. A water-soluble protein

15. Dissociation • Dissociation of water: • H2O H+ + OH- • Dissociation of other things: • Ex: HCl H+ + Cl- • Acids yield H+ions • Bases yield OH- ions

16. Chemical reaction: hydrogen bond shift

17. 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

18. Each step in pH scale is an order of magnitude (x10) pH

19. The effects of acid precipitation on a forest

20. Pulp mill

21. Acid rain damage to statuary, 1908 & 1968

22. 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

23. 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

24. Water Movement Water moves across a selectively permeable membrane

25. 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

26. 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

27. Question 3 Which of the following is an example of a hydrophobic material? • Paper • Table salt • Wax • Sugar • Pasta

28. 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%

29. 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

30. 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