1. Water

2. Penny Lab Water has several important water properties that we will explore this week. Title your lab report “Penny Lab” and add it to your table of contents. First observation: How many drops of water can one penny hold?

3. Hypothesis Question: How does soap affect the amount of water one penny can hold? If…then…

4. Materials 2 pennies 2 dropper 1 beaker with water 1 beaker with soapy water

5. Experimental Design We are going to test if the amount of soap makes a difference Each group will have a different amount of soap in their soapy water We will compile class data and see what our results are

6. White Board How much soap did you have in your soapy water? What was your hypothesis? What happened? Was your hypothesis supported or rejected? Draw a bar graph to compare your averages or tap water and soapy water. Answer one post lab question (teacher assigns)

7. Completing the Lab Draw your graph in your notebook. Look at class data. Describe if an increase in soapy water effected surface tension of water. Answer post lab analysis questions in your notebook. Write in complete sentences. Clean up your area

8. Water Race 3 drops of water 1 toothpick Who will be the quickest at each table?

9. Challenge Round! Who will be our classroom champion??

10. Water What were some initial observations about your drop of water? What were some observations you made while you were in the race?

11. Properties of Water Polar molecule Cohesion and adhesion High specific heat Density – greatest at 4 o C Universal solvent of life

12. Polarity of Water Two hydrogen atoms form single polar covalent bonds with an oxygen atom. This gives water more structure than other liquids Because oxygen is more electronegative, the region around oxygen has a partial negative charge. A water molecule is a polar molecule with opposite charges on each end of the molecule. Draw a water molecule with charges.

13. Water has a variety of unusual properties because of attractions between these polar molecules. –The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules –They form a hydrogen bond. –Each water molecule can form hydrogen bonds with up to four neighbors. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.1

14. HYDROGEN BONDS Hold water molecules together Each water molecule can form a maximum of 4 hydrogen bonds The hydrogen bonds joining water molecules are weak –about 1/20 th as strong as covalent bonds. They form, break, and reform with great frequency Extraordinary Properties that are a result of hydrogen bonds. –Cohesive behavior –Resists changes in temperature –High heat of vaporization –Expands when it freezes –Versatile solvent

15. Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion. –Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. –Water behaves as if covered by an invisible film. –Some animals can stand, walk, or run on water without breaking the surface. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.3

16. Cohesion vs. Adhesion

17. Organisms Depend on Cohesion Cohesion is responsible for the transport of the water column in plants Cohesion among water molecules plays a key role in the transport of water against gravity in plants Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels. Hydrogen bonds hold the substance together, a phenomenon called cohesion

18. Exploring pH What do you already know?

19. Exploring pH What is pH measuring? What does the H stand for? Think of the water molecule If we take away an H+, what is left?

20. Data Table SolutionpH[H + ]pOH[OH - ] Tap water Distilled water Milk Salt Sugar PowerAde Soda Lemon Juice Bleach Corn Syrup Vinegar Glass cleaner Dish detergent Hand soap

21. White Board How can you organize these numbers? Draw a solution and put them in order What do you think is happening?

22. Soil at a high pH makes hydrangea flowers pink Soil at a low pH makes hydrangea flowers blue pH Key Concepts

23. p H doesn’t just tell us if a solution is neutral, an acid or a base It also tells us: the concentration of H + ions in the solution in moles/L Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 pH and [H + ] pH Key Concepts

24. p H doesn’t just tell us if a solution is neutral, an acid or a base It also tells us: the concentration of H + ions in the solution in moles/L which is expressed as a p ower of 10 Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 pH and [H + ] pH Key Concepts

25. Power of 10 A negative exponent means the number is less than 1 pH Key Concepts

26. Definition of pH: pH = –log[H + ] Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 Do not forget the “–” sign! logarithm: in base 10, a number A derived from another number B such that 10 B =A. The number 7 is the logarithm of 0.000 000 1 pH and [H + ] pH Key Concepts

27. Dissociation of water: H 2 O(l) H + (aq) + OH – (aq) [H + ] and [OH – ] are related pH for bases [H + ][OH - ] = 1 x 10 -14 Becomes: pH + pOH = 14 pH Key Concepts

28. Household chemical Acid or basepH ammoniabase11 bar soapbase10 baking sodabase8.5 soda wateracid4 vinegaracid3 lemon juiceacid2 pH range pH can be less than 0 for stronger acids greater than 14 for stronger bases pH Key Concepts

29. Measuring pH The color of red cabbage juice at different pH You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH - using a chemical that changes color at different pH values (pH indicators) pH Key Concepts

30. Measuring pH You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH - using a chemical that changes color at different pH values (pH indicators) pH Key Concepts

31. You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH - using a chemical that changes color at different pH values (pH indicators) - measuring the electrical properties of the solution Measuring pH Acids and bases conduct electricity pH and conductivity (flow of electricity) are related a pH meter pH Key Concepts

32. Most biochemical reactions involve solutes dissolved in water. There are two important quantitative proprieties of aqueous solutions. –1. Concentration –2. pH

33. Concentration of a Solution Molecular weight – sum of the weights of all atoms in a molecule (daltons) Mole – amount of a substance that has a mass in grams numerically equivalent to its molecular weight in daltons. Avogadro’s number – 6.02 X 10 23 –A mole of one substance has the same number of molecules as a mole of any other substance.

34. Molarity The concentration of a material in solution is called its molarity. A one molar solution has one mole of a substance dissolved in one liter of solvent, typically water. Calculate a one molar solution of sucrose, C 12 H 22 O 16. C = 12 daltons H = 1 dalton O = 16 daltons 12 x12 = 144 1 x 22 = 22 16 x 11 = 176 342 For a 2M solution? For a.05 M solution? For a.2 M solution?

35. Occasionally, a hydrogen atom shared by two water molecules shifts from one molecule to the other. –The hydrogen atom leaves its electron behind and is transferred as a single proton - a hydrogen ion (H + ). –The water molecule that lost a proton is now a hydroxide ion (OH - ). –The water molecule with the extra proton is a hydronium ion (H 3 O + ). Dissociation of Water Molecules Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Unnumbered Fig. 3.47

36. A simpler way to view this process is that a water molecule dissociates into a hydrogen ion and a hydroxide ion: –H 2 O H + + OH - This reaction is reversible. At equilibrium the concentration of water molecules greatly exceeds that of H + and OH -.

37. In pure water only one water molecule in every 554 million is dissociated. –At equilibrium, the concentration of H + or OH - is 10 -7 M (25°C).

38. Acids and Bases An acid is a substance that increases the hydrogen ion concentration in a solution. Any substance that reduces the hydrogen ion concentration in a solution is a base. –Some bases reduce H + directly by accepting hydrogen ions. Strong acids and bases completely dissociate in water. Weak acids and bases dissociate only partially and reversibly.

39. pH Scale The pH scale in any aqueous solution : –[ H + ] [OH - ] = 10 -14 Measures the degree of acidity (0 – 14) Most biologic fluids are in the pH range from 6 – 8 Each pH unit represents a tenfold difference (scale is logarithmic) –A small change in pH actually indicates a substantial change in H + and OH - concentrations.

40. Problem How much greater is the [ H + ] in a solution with pH 2 than in a solution with pH 6? Answer: pH of 2 = [ H + ] of 1.0 x 10 -2 = 1/100 M pH of 6 = [ H + ] of 1.0 x 10 -6 = 1/1,000,000 M 10,000 times greater

41. Buffers A substance that eliminates large sudden changes in pH. Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life. –Are combinations of H + acceptors and donors forms in a solution of weak acids or bases –Work by accepting H + from solutions when they are in excess and by donating H + when they have been depleted.

42. Acid Precipitation Rain, snow or fog with more strongly acidic than pH of 5.6 West Virginia has recorded 1.5 East Tennessee reported 4.2 in 2000 Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphere –Lowers pH of soil which affects mineral solubility – decline of forests –Lower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.

43. Salt Water vs. Fresh Water Boiling Point Freezing Point Gummy Bear Osmosis

44. Freezing Point What happens to salt water after 1 hour in the freezer? Independent variable? Dependent variable? Control? Hypothesis: If… then…

45. Gummy Bear Osmosis Read through handout Define roles for each group member and write them down Measurements and Lab set up Day 2 Friday Day 3 Monday Lab report will be due Tuesday beginning of class

46. Ice Cream Composition

47. Freezing Point What happened to salt water after 1 hour in the freezer? Was it what you expected? Analyze the results Exit Ticket: Draw a sketch of salt water molecules

48. Boiling Point What happens to salt water after 1 hour in the freezer? Independent variable? Dependent variable? Control?

49. Moderates Temperatures on Earth What is kinetic energy? Heat? Temperature? Calorie? What is the difference in cal and Cal? What is specific heat? Celsius Scale at Sea Level 100 o CWater boils 37 o CHuman body temperature 23 o CRoom temperature 0oC0oCWater freezes Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.

50. Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for: 1.Prevention of temperature fluctuations that are outside the range suitable for life. 2.Coastal areas having a mild climate 3.A stable marine environment Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1 o C.

51. Evaporative Cooling The cooling of a surface occurs when the liquid evaporates This is responsible for: –Moderating earth’s climate –Stabilizes temperature in aquatic ecosystems –Preventing organisms from overheating

52. Density of Water Most dense at 4 o C Contracts until 4 o C Expands from 4 o C to 0 o C The density of water: 1.Prevents water from freezing from the bottom up. 2.Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation. 3.Makes transition between season less abrupt.

53. –When water reaches 0 o C, water becomes locked into a crystalline lattice with each molecule bonded to to the maximum of four partners. –As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state. –Ice is about 10% less dense than water at 4 o C. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.5

54. Solvent for Life Solution –Solute –solvent Aqueous solution Hydrophilic –Ionic compounds dissolve in water –Polar molecules (generally) are water soluble Hydrophobic –Nonpolar compounds