Chapter 3. Water: Supports All Life. Hydrogen Bonding of water. Slide 1 / 44. Slide 2 / 44. Slide 3 / 44. Slide 4 / 44. Slide 6 / 44.

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1 hapter 3 Slide 1 / 44 Slide 2 / 44 Water: Supports ll Life Water and the Fitness of the nvironment Water is the biological medium on arth ll living organisms require water more than any other substance Most cells are surrounded by water, and cells consist of about 70-95% water Slide 3 / 44 Slide 4 / 44 Water and arth ydrogen onding of water The polarity of water molecules results in hydrogen bonding Three-quarters of the arth s surface is submerged in water - The water molecule is a polar molecule due to uneven distribution of electrons. The opposite ends of a water molecule have opposite charges. The abundance of water is the main reason the arth is habitable + + Slide 5 / 44 Slide 6 / 44 Polarity The polarity of water molecules allows them to form hydrogen bonds with each other and contributes to the various properties water exhibits 1 In a single molecule of water, the two hydrogen atoms are bonded to a single oxygen atom by hydrogen bonds. nonpolar covalent bonds. polar covalent bonds. ionic bonds. van der Waals interactions. click here for an animation about water

2 Slide 7 / 44 Slide 8 / 44 2 The slight negative charge at one end of one water molecule is attracted to the slight positive charge of another water molecule. What is this attraction called? a covalent bond a hydrogen bond an ionic bond a hydrophilic bond a hydrophobic bond Four properties of water ll contribute to arth s fitness for life ohesive behavior bility to moderate temperature xpansion upon freezing Versatility as a solvent Water molecules exhibit cohesion ohesion is the bonding of a high percentage of the molecules to neighboring molecules ohesion is due to hydrogen bonding Slide 9 / 44 ohesion ohesion helps pull water up through the microscopic vessels of plants dhesion of water to plant cell walls also helps counteract the force of gravity Slide 10 / 44 ohesion and dhesion Water conducting cells 100 µm click here for a video on cohesion and adhesion 100 mm Slide 11 / 44 Slide 12 / 44 Surface Tension 3 What determines the cohesiveness of water molecules? Surface tension is related to cohesion It is a measurement of how hard it is to break the surface of a liquid hydrophobic interactions nonpolar covalent bonds ionic bonds hydrogen bonds both and

3 Slide 13 / 44 4 Which of the following is possible due to the high surface tension of water? Slide 14 / 44 5 What do cohesion, surface tension, and adhesion have in common with reference to water? Lakes don't freeze solid in winter, despite low temperatures. water strider can walk across the surface of a small pond. Organisms resist temperature changes, although they give off heat due to chemical reactions. Water can act as a solvent. ll increase when temperature increases. ll are produced by ionic bonding. ll are properties related to hydrogen bonding. ll have to do with nonpolar covalent bonds. and only The p of water remains exactly neutral. Slide 15 / 44 Moderation of Temperature Slide 16 / 44 Review: eat and Temperature Water moderates air temperature by absorbing heat from warmer air and releasing the stored heat to cooler air. Kinetic energy is the energy of motion eat is a measure of the total amount of kinetic energy due to molecular motion Temperature measures the intensity of heat due to average K of molecules Water can absorb or release a large amount to heat with only a slight change in its own temperature. Slide 17 / 44 Water s igh Specific eat Slide 18 / 44 ydrogen onding and Specific eat Water has a high specific heat, which allows it to minimize temperature fluctuations to within limits that permit life The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1º. eat must be absorbed in order to break hydrogen bonds eat is released when hydrogen bonds form

4 vaporation is the transformation of a substance from a liquid to a gas eat of vaporization is the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas Slide 19 / 44 vaporation vaporative cooling is a process in which as liquid evaporates, its remaining surface cools vaporative cooling is due to water s high heat of vaporization vaporative cooling of water helps stabilize temperatures in living things and in bodies of water Slide 20 / 44 vaporative ooling Slide 21 / 44 6 Water's high specific heat is mainly a consequence of the small size of the water molecules. high specific heat of oxygen and hydrogen atoms. absorption and release of heat when hydrogen bonds break and form. fact that water is a poor heat conductor. inability of water to dissipate heat into dry air. The hydrogen bonds in ice are more ordered than in liquid water, making ice less dense, and able to float. Slide 22 / 44 Floating Ice Slide 23 / 44 Slide 24 / 44 The Solvent of Life Water can also interact with large polar molecules such as proteins. Ionic and polar regions on the protein s surface attract water molecules. Lysozyme molecule in a nonaqueous environment. Lysozyme molecule in an aqueous environment such as tears or saliva.

5 Slide 25 / 44 7 Ice is lighter and floats in water because it is a crystalline structure in which each water molecule is bonded to a maximum of four other water molecules by which kind of bond? ionic hydrogen covalent and only,, and Slide 26 / 44 ydrophilic and ydrophobic Substances hydrophobic substance does not have an affinity for water hydrophilic substance has an affinity for water Slide 27 / 44 Solute oncentration in queous Solutions Slide 28 / 44 queous Solutions alculations Most biochemical reactions occur in water Therefore, it is important to learn to calculate the concentration of solutes in an aqueous solution mole represents an exact number of molecules of a substance, 6.02 x Molarity is the number of moles of solute per liter of solution oncentrations of aqueous solutions may also be measured in mass percent, e.g. 10% salt solution Slide 29 / 44 Slide 30 / 44 issociation of water issociation of water molecules leads to acidic and basic conditions that affect living organisms Water can dissociate into hydronium ions and hydroxide ions hanges in the concentration of these ions can have a great affect on living organisms + O O ydronium ion (3O + ) click here for an animation about hydrogen bonding ydroxide ion (O )

6 Slide 31 / 44 ffects of hanges in p oncentrations of + and O - are equal in pure water dding certain solutes, called acids and bases, modifies the concentrations of + and O - iologists use the p scale to describe how acidic or basic (or alkaline) a solution is + base is any substance that reduces the hydrogen ion concentration of a solution Slide 32 / 44 cids and ases n acid is any substance that increases the hydrogen ion concentration of a solution. O- Slide 33 / 44 Slide 34 / 44 The p Scale The p of a solution is determined by the relative concentration of hydrogen ions The p of acids are low, below 7 The p of bases are above 7 up to 14 Most biological fluids have p values around 6-8 The p Scale The p scale and p values of various aqueous solutions Increasingly cidic [+] > [O ] Neutral [+] = [O ] Increasingly asic [+] < [O ] Slide 35 / 44 uffers Slide 36 / 44 cid Precipitation The internal p of most living cells must remain close to p 7 uffers are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution cid precipitation refers to rain, snow, or fog with a p lower than p 5.6 They consist of an acid-base pair that reversibly combines with hydrogen ions aused primarily by the mixing of different pollutants with water in the air

7 Slide 37 / 44 cid Precipitation Slide 38 / 44 8 given solution contains (10-4 ) moles of hydrogen ions [+] per liter. Which of the following best describes this solution? cid precipitation can damage life in arth s water and soil ecosystems, such as lakes, streams and forests More 12 basic More acidic cid rain Normal rain acidic: + acceptor basic: + acceptor acidic: + donor basic: + donor neutral Slide 39 / 44 Slide 40 / 44 9 What would be the p of a solution with a hydrogen ion [ + ] concentration of 10-8 M? p = - log [ + ] 10 What would be the p of a solution with a hydroxide ion [O - ] concentration of M? K w = p 2 p 4 p 6 p 8 p 10 p 2 p 4 p 10 p 12 p 14 Slide 41 / Which of the following solutions has the greatest concentration of hydrogen ions [ + ]? Slide 42 / Which of the following statements is true about buffer solutions? They maintain a constant p when bases are added to them but not when acids are added to them. gastric juice at p 2 vinegar at p 3 tomato juice at p 4 black coffee at p 5 household bleach at p 12 They maintain a constant p when acids are added to them but not when bases are added to them. They maintain a constant p of exactly 7 in all living cells and biological fluids. They maintain a relatively constant p. They are found only in living systems and biological fluids.

8 Slide 43 / 44 Slide 44 / uffers are substances that help resist shifts in p by releasing + in acidic solutions. donating + to a solution when they have been depleted. releasing O- in basic solutions. accepting + when they are in excess. both and