1. Chapter 2 The Chemistry of Life Sec. 2-2 Properties of Water

2. The Water molecule - polarity H 2 O Water is a polar molecule A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.  Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap

3. The Water Molecule - Polarity 2 H atoms and 1 O atom are covalently bonded –O end has partial negative charge (-) –H end has partial positive charge (+)  Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap

4. The Water Molecule - Polarity The larger nucleus of the oxygen atom with its 8 protons (8 positive charges) has a greater attraction for hydrogen’s electrons than does hydrogen’s one proton nucleus (1 positive charge).  Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap

5. Weak Bonds between H 2 O molecules The partial negative charge (-) of the O end of one H 2 O molecule and the partial positive charge (+) of the H end of another H 2 O molecule are attracted to one another (like magnets). Water molecule  Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

7. Partial Positive end of H 2 0 molecule Partial Negative end of H 2 0 molecule Hydrogen bonds     

8. Hydrogen Bonds between H 2 O molecules These between molecule attractions are known as hydrogen bonds. Water molecule  Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

9. Hydrogen Bonds between H 2 O molecules Hydrogen bonds (between H 2 O molecules) are not as strong as covalent or ionic bonds. Water molecule  Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

10. Results of Hydrogen Bonding - Cohesion Cohesion is an attraction between molecules of the same substance (co- means common). Because of its hydrogen bonding, H 2 O is extremely cohesive. Water molecule Hydrogen bonds  Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

11. Results of Hydrogen Bonding - Cohesion One result of the cohesion of H 2 O molecules is surface tension –The tight film that forms on the surface of water that allows some spiders and insects to walk on a pond’s surface. Water molecule Hydrogen bonds  Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

12. Results of Hydrogen Bonding - Adhesion Adhesion is an attraction between molecules of different substances. (ad- means toward) Water molecule Hydrogen bonds Cohesion  Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

13. Adhesion

14. Results of Hydrogen Bonding - Adhesion Capillary action, the tendency of H 2 O to be drawn up narrow tubes, results from the strong adhesive force of H 2 O. Water molecule Hydrogen bonds Cohesion  Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

15. Capillary Action

16. Another Result of Hydrogen Bonding is that… Before molecules of water gain or lose thermal energy (i.e. the temperature goes up or down)… H-bonds must be broken or formed. This makes water resistant to temperature increases or decreases. Water molecule Hydrogen bonds Cohesion Adhesion  Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

17. Which will make larger droplets, hot or cold water? Which will stick to your windshield longer, hot or cold water? Are you pondering what I’m pondering?

18. Water in combination A mixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change  Water in combination Acids, bases, and pH Buffers Recap 

19. Water in combination Water forms two types of mixtures: –Solutions –Suspensions Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change  Water in combination Acids, bases, and pH Buffers Recap 

20. Water in combination A solution is a mixture in which all of the components are evenly distributed throughout. A solute (sol’ yoot) is the substance that is dissolved in a solution. (ex. table salt in a saltwater solution) A solvent is the substance in which the solute dissolves. (ex. the water in which salt dissolves to make a saltwater solution). Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change  Water in combination Acids, bases, and pH Buffers Recap 

21. Solution Cl - Water Cl - Na + Water Na + Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change  Water in combination Acids, bases, and pH Buffers Recap  Fig. 2-9, pg. 42

22. Water in combination Water forms two types of mixtures: –Solutions –Suspensions Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change  Water in combination Acids, bases, and pH Buffers Recap 

23. Water in combination (suspension) A suspension is a mixture of water and nondissolved material. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change  Water in combination Acids, bases, and pH Buffers Recap  Flour in water

24. Acids, Bases, and pH Acidity and Alkalinity (better than having to say “basicity”) are determined by the relative number of H + (hydrogen) ions compared to the number of OH - (hydroxide) ions in a solution. Acids have more H + than OH - Bases have more OH - than H + Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

25. Acids, Bases, and pH Chemists devised a scale to measure acidity called the pH scale. The pH scale ranges between 0 and 14 with values below 7 indicating acids and values above 7 indicating bases. At pH 7, a solution is neutral (neither acid nor base). This is the point at which a solution has the same number of H + and OH - ions. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

26. 01234567891011121314 pH scale acid neutralbase

27. Acids, Bases, and pH Pure H 2 O has a pH of 7 because when H 2 O dissociates (which is quite rarely)… H 2 O H + + OH - –Water hydrogen ion + hydroxide ion Equal numbers of H + and OH - are formed Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

28. Acids, Bases, and pH Oven cleaner Bleach Ammonia solution Soap Sea water Human blood Pure water Milk Normal rainfall Acid rain Tomato juice Lemon juice Stomach acid Neutral Increasingly Basic Increasingly Acidic

29. Acids, Bases, and pH When strong acids are placed in H 2 O, they dissociate almost completely. HCl H + + Cl - The concentration of H + increases greatly and there are now many more H + ions than OH - ions. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

30. Acids, Bases, and pH pH is below 7 Acids have a sharp or sour taste. ex. Lemons, vinegar, tomatoes, coffee Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

31. Acids, Bases, and pH When strong bases are placed in H 2 O, they also dissociate almost completely. NaOH Na + + OH - The concentration of OH - increases greatly and there are now many more OH - ions than H + ions. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

32. Acids, Bases, and pH pH is above 7. Bases have a bitter taste and feel slippery when in water. Ex. ammonia Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap  Al Kaline (get it?)

33. Acids, Bases, and pH - Recap Acidic solutions contain higher concentrations of H + ions than pure water and have pH values below 7. Basic, or alkaline, solutions contain lower concentrations of H + ions than pure water and have pH values above 7. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination  Acids, bases, and pH Buffers Recap 

34. Buffers The chemical reactions that keep living things alive only operate within a narrow pH range –This involves the process of HOMEOSTASIS. Buffers keep the pH within this range. Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH  Buffers Recap 

35. Buffers A buffer is a weak acid or base that reacts with strong acids or bases to prevent sharp, sudden changes in pH. Buffers do this by taking up excess H + and OH - ions. Example – buffered aspirin (Bufferin) Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH  Buffers Recap 

36. Recap – The Properties of Water waterH2OH2O polar H-bonding cohesionadhesion Capillary action Attraction between H 2 O molecules Uneven distribution of electrons Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers  Recap 

37. End of 2-2  

38. Recap Water molecule Hydrogen bonds Cohesion Adhesion Resistance to temperature change Water in combination Acids, bases, and pH Buffers  Recap 

39. pH SCALE

40. Water is resistant to temperature change Do you think water makes larger droplets when it is cold or hot? Do you think water will stick to your windshield better when it is cold or hot? Water molecule Hydrogen bonds Cohesion Adhesion  Resistance to temperature change Water in combination Acids, bases, and pH Buffers Recap 

41. δ

42. Partial negative charge ++ -- ++ ++ -- ++ ++ -- ++ ++ -- ++

44. Acids, Bases, and pH When strong acids are placed in H 2 O, they dissociate almost completely. HCl  H + + Cl - The concentration of H + increases greatly and there are now many more H + ions than OH - ions. pH is below 7 Acids have a sharp or sour taste. ex. Lemons, vinegar, tomatoes, coffee Water molecule Hydrogen bonds Cohesion Adhesion Water in combination  Acids, bases, and pH Buffers Recap 