Water

1. Water

2. Water • Most abundant compound in living things • Important to understanding the functions of living things • Composed of 2 hydrogens and 1 oxygen • Atoms connected through a covalent bond = sharing electrons; creates some unique properties

3. Water • Polarity – happens because oxygen atom has greater attraction for electrons than the hydrogen atom; creates magnet-like polarity

5. Water • Hydrogen bonding – happens due to polarity; attracts water molecules to each other • Both responsible for many of water’s special properties.

8. Water • Hydrogen bonding pulls water molecules together & creates cohesion • Cohesion – attraction between molecules of same substance • Water = extremely cohesive; allows bugs to “walk” on water • Creates surface tension

9. Water • Adhesion – attraction between molecules of different substances • Makes water stick to sides of containers • Ex. Measuring cup, graduated cylinder • Also makes water rise in a narrow tube = capillary action • Capillary action helps water get pulled up from roots of plants to leaves.

10. Water • Has a high specific heat = amount of energy needed to increase the temperature • In order for temperature to increase, the molecules must move faster • Hydrogen bonds in water make it hard for the molecules to move faster • Means that areas near water stay cooler in summer because the water takes longer to heat and warmer in winter because the water holds a lot of heat.

11. Water • Density anomaly – water is more dense as a liquid than as a solid • Allows ice (solid) to float on surface of lakes & rivers • Permits life to survive in liquid water below the surface • Without this property – aquatic life would all die each winter as bodies of water freeze

12. Water • Universal solvent – water is able to dissolve a lot of compounds • Necessary for chemical reactions to take place in body= metabolism • Without being dissolved, these reactions would not occur

13. Solutions

14. What are solutions? • Solutions are homogeneous mixtures What does THAT mean? • Particles are EVENLY distributed or mixed • May exist as a SOLID, LIQUID or GAS

15. What are solutions? • Particles are SMALL – about 0.1 to 1 nm • Will not separate if left standing • Will not separate by filtration • Do not display Tyndall effect = scattering of light beam that is shone through the mixture

16. Examples • Air • Salt in water • Steel, brass (metal alloys)

17. What is in a solution? • Solutions consist of: • Solvent = the substance that does the dissolving that is present in the GREATER amount • Solute = substance that is placed in solvent, present in SMALLER amount

18. How do solutions form? • Whensolvent particles are attracted to solute particles Hey, I really am attracted to you! Me too!

19. How do solutions form? • If the attractive forces between solvent & solute particles are greater than or stronger than the attractive forces between particles of the SOLUTE, then the solute is called SOLUBLE and WILL DISSOLVE.

20. Ionic Solutes • When an ionic substance dissolves in water, the ions separate and are able to move in the water. • Process is called dissociation

21. The Dissociation Process NaCl (cr) + H2O  Na+(aq) + Cl-(aq) Dissociated ion

22. Ionic Solutes • Because the ions can now move, the resulting solution can conduct electricity • Conductivity requires 2 things: 1. Charged particles 2. Ability of the charged particles to move • Before dissolving, these conditions do not exist

23. Ionic Solutes • This property of conducting electricity when in solution classifies the solute as an electrolyte • Electrolyte = substance that forms ions when it dissolves in water

24. Molecular Solutes • Molecular solutes contain no charged particles • Most do not form ions when dissolved • Molecules tend to stay whole when they go into solution • Process = dispersion • Dispersion = breaking into small pieces that spread throughout the solution

25. Molecular Solutes • After dispersion, some molecular compounds form ionsby reacting with water to gain or lose electrons • Ionization = process by which molecules gain or lose electrons • Allows them to be electrolytes as well • Does not happen to all molecules

26. What affects the speed that something dissolves?

27. Think about it…. • In winter, you make a cup of hot tea and add a spoonful of sugar. When you finish drinking your tea, there is no sugar at the bottom of your cup. • In summer, you have the same size cup of iced tea and add the same amount of sugar. Yet, at the bottom of the cup when you are done, there is some visible sugar “sludge” left. • Why?

28. Temperature • When the temperature of something increases the particles are moving faster • So, if we heat up our solvent, the particles move faster and pull apart the solute faster

29. Surface Area • The smaller the particle, the greater the surface area of that solute that is exposed to the solvent. • Smaller particles = faster dissolving due to increased surface area

30. Surface Area • So – which should dissolve faster: Sugar cube Granulated sugar • Why? • Greater surface area!

31. Stirring • Stirring makes the solute and solvent particles have more contact with each other • More contact = faster dissolving

32. Types of solutions

33. Saturated solution • A solution that contains the maximum amount of solute. • So if I add more solute to this solution, no more will dissolve

34. Unsaturated solutions • A solution that contains less than the maximum amount of solute • So if I add more solute to this solution, it WILL dissolve

35. Supersaturated Solutions • A solution that contains more than the maximumamount of solute for a saturated solution at the same temperature • How is this possible? • Make a saturated solution • Heat and add more solute • Cool slowly and carefully

36. So – how do I identify an unknown solution? • Drop asmall piece of the solute into the solution • If it DISSOLVES RIGHT AWAY – the solution is unsaturated • If it DROPS TO THE BOTTOM – the solution is saturated • If it causes MORE CRYSTALS TO APPEAR – the solution is supersaturated

37. What do all ofthese have in common? APPLE BUTTER MALIC ACID BUTYRIC ACID GRAPEFRUIT CITRIC ACID VINEGAR ACETIC ACID MILK LACTIC ACID ACIDS!!! VOMIT BATTERIES HYDROCHLORIC ACID SULFURIC ACID WINE PEPSI TARTARIC ACID PHOSPHORIC ACID

38. What is an acid? • Acids (defined) A substance which forms a lot of H+ ions in solution with water

39. What is an acid? • Characteristics a) Taste sour b) Conduct electricity when in dissolved in water = electrolyte c) React with bases to form water and a salt = neutralization reaction d) Change indicator colors e) More H+ than water.

40. What is a base? • Base (defined) A substance which forms a lot of OH- ions in water (or very few H+ ions)

41. What is a base? • Characteristics a) Bitter taste b) Have a slippery or soapy feeling c) Are caustic d) React with acids in a neutralization reaction. e) Conduct electricity when dissolved in water f) Change indicator colors g) Less H+ than water

42. What is pH? • A quantitative measure of the strength of acids and bases • Actually measures the amount of H+ (the acid ion) in a solution

43. pH scale [OH--] > [H+] [H+]>[OH--] 0---------------------7--------------------14 BASIC ACIDIC NEUTRAL

44. Why is water neutral? So solution is neutral H+ H+ OH— H+ OH— OH— H+ OH— H+ OH— OH— ions The number of H+ions =

45. pH pH between 1 & 7 = acidic Means a lot of H+ ions in water Created by acids The lower the pH the stronger the acid

46. Acidic Solution So solution is acidic Add HCl (add H+) H+ H+ H+ OH— H+ OH— OH— Acid Ion H+ H+ H+ OH— OH— H+ H+ [OH—] [H+] >

47. pH pH between 7 & 14 = basic/alkaline Means very few H+ ions in water Created by bases The higher the pH, the stronger the base

48. Basic Solution Add NaOH (add OH—) OH— So solution is basic H+ H+ OH— H+ OH— OH— OH— Base Ion H+ OH— H+ OH— [OH—] [H+] <

49. Buffers • Weak acids/bases that prevent sudden changes in pH • Example = blood, sea water

50. Buffers Important to living organisms because pH must be controlled in order for homeostasis to be maintained