2. Chemistry of Life Properties of Water Chapter 3

3. Pre Assessment 1.What causes water to travel up the roots of a plant? 2.What allows bugs to walk on top of water? 3.Why does ice float in water if they are both the same compounds? 4.Draw a pH scale and label-acids, bases, and neutral substances. 5.Why is water known as the universal solvent?

4. Pre Assessment Answers

5. Water Why are we studying water? All life occurs in water  inside & outside the cell All life occurs in water  inside & outside the cell Makes up 70-90% of all living things. 75% of the earth’s surface is covered with water Makes up 70-90% of all living things. 75% of the earth’s surface is covered with water

6. Figure 3.x1 Water

7. Chemistry of water H 2 O molecules form H-bonds with each other – +H attracted to –O – creates a sticky molecule

8. Water Molecules Hydrogen bonds~ relatively weak bonds last only 1/billionth of a second in liquid water, but are constantly broken and reformed. Polar —shared electrons of the covalent bonds spend more time around the oxygen atom than they do around the hydrogen nuclei. water animation

9. Elixir of Life Special properties of water 1.cohesion & adhesion surface tension, capillary action 2.Good solvent many molecules dissolve in H 2 O hydrophilic vs. hydrophobic 3.Lower density as a solid ice floats! 4.High specific heat water stores heat 5.High heat of vaporization heats & cools slowly Ice! I could use more ice!

10. 1. Cohesion & Adhesion Walking on water Cohesion – H bonding between H 2 O molecules – water is “sticky” surface tension drinking straw Adhesion – H bonding between H 2 O & other substances capillary action meniscus water climbs up paper towel or cloth

11. Water molecules are cohesive and adhesive. Cohesion— water molecules cling to other water molecules because of hydrogen bonding. Adhesion— water molecules adhere to polar surfaces because they have positive and negative poles (polarity).

12. How does H 2 O get to top of trees? Transpiration is built on cohesion & adhesion That’s cool!!

13. 2. 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

14. What dissolves in water? Hydrophilic – substances have attraction to H 2 O – Philic=affinity – polar or non-polar?

15. Figure 3.7 A crystal of table salt dissolving in water

16. Figure 3.8 A water-soluble protein

17. What doesn’t dissolve in water? Hydrophobic – substances that have an attraction to H 2 O – Phobic= fear – polar or non-polar? fat (triglycerol) Oh, look hydrocarbons!

18. 3. The special case of ice Most (all?) substances are more dense when they are solid, but not water… Ice floats! – H bonds form a crystal And this has made all the difference!

19. Ice floats

20. Figure 3.5x1 Ice, water, and steam

21. 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 sinking cold H 2 O cycles nutrients in autumn

22. 4. 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

23. Water has a high heat capacity. specific heat—the amount of heat a given amount of a substance requires for an increase in temperature. Examples: water = 1 ethyl alcohol = 0.6 sucrose = 0.3 liquid ammonia = 1.23 calorie —the amount of heat that will raise the temperature of 1 g (1 mL or 1 cc) of water 1 o Celsius.

24. 5. Heat of vaporization Evaporative cooling Organisms rely on heat of vaporization to remove body heat

25. Water has a high heat of vaporization. It requires 540 calories of heat energy to convert 1 g of the hottest water to a gas. – This is 60 X as much as for ether and 2X as much as for ammonia. Why does water have this high heat of vaporization? Hydrogen bonds must be broken before water boils and water molecules vaporize.

26. Why does water have a high heat capacity? The many hydrogen bonds that link water molecules help it to absorb heat without a great change in temperature. What are the consequences of this property to living things? Because the temperature of water rises and falls slowly, organisms are better able to maintain their normal internal temperatures and are protected from rapid temperature changes (Homeostasis)

27. Evaporative cooling I feel the evaporative cooling

28. 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 –

29. 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 tenfold change in H+ ions pH1  pH2 10 -1  10 -2 10 times less H + pH8  pH7 10 -8  10 -7 10 times more H + pH10  pH8 10 -10  10 -8 100 times more H +

30. Check Point Acid –Base-or Neutral??? 1.pH of 8.4 2.A solution with more H+ ions the OH- ions 3.A solution with an equal amount of H+ ions and OH- ions 4.A pH of 7 5.A base and an acid combined

31. Check Point Acid –Base-or Neutral???

32. 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

33. Solutions Solvent— the substance that does the dissolving Solute— the substance that is dissolved Solution— a homogeneous mixture that will not separate upon standing

34. Aqueous Solutions Mole— the number of grams of a substance that equals its molecular weight in daltons. Example: sucrose, C 12 H 22 O 11 12 carbons = 144 22 hydrogens =22 11 oxygens = 176 One mole is equal to 342 grams. To make a 0.5 M solution, add water to 171 grams to make 1 Liter of solution.

35. He’s gonna earn a Darin Award! Any Questions?

36. Post Assesment 1.Name a benefit of cohesion and adhesion to animals and plants. 2.Name a solution-identify the solute and the solvent. 3.Name an example of a neutral substance in our bodies. 4.Name an a solution in our bodies that is acidic? How does it get neutralized? 5.How many times more acidic is a solution with a pH of 1 than a solution with a pH of 2?

37. Post Assessment Answers