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CHAPTER 3 Water and Life CH 3 Learning Objectives 1 Explain how hydrogen bonding results from polar covalent bonds 2 Identify four properties of water that are important for life and describe how they result from hydrogen bonding 3 Differentiate between an acid and a base define pH and describe how it affects the processes of life I would suggest completing the crossword puzzle to help you understand the terminology and correlate how the terms relate to topics covered in this chapter Figure 3 1b CONCEPT 3 1 Polar covalent bonds in water molecules result in hydrogen bonding In the water molecule the electrons of the polar covalent bonds spend more The water molecule is thus a polar molecule the overall charge Polarity allows water molecules to form CONCEPT 3 2 Four emergent properties of water contribute to Earth s suitability for life Four of water s properties that facilitate an environment for life are 1 2 ability to 3 expansion 4 versatility 1 Cohesion of Water Molecules Collectively hydrogen bonds hold water molecules together a Cohesion results in high surface tension a measure of how difficult it is to stretch or Cohesion contributes to the transport of water and dissolved nutrients against Adhesion is an attraction between different substances for example between This helps to counter the 2 Moderation of Temperature by Water Water absorbs heat from warmer air and releases Water can absorb or release a large amount of heat stored with only a slight Temperature and Heat Kinetic energy is the The kinetic energy associated with random motion of Temperature represents the average kinetic energy atoms or molecules is of the molecules in a matter to another is Thermal energy in transfer from one body of A calorie cal is the amount of heat required to raise or cool the temperature of 1 g of water by 1 C Food Calories are kilocalories kcal or The joule J is another unit of energy 1 J 0 239 cal or 1 cal 4 184 J Water s High Specific Heat The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 C The specific heat of water is 1 cal g C Water resists changing its temperature because of its Water s high specific heat can be traced to Heat is absorbed when Heat is released when The high specific heat of water minimizes temperature fluctuations to A large body of water can absorb and store a huge amount of heat from the sun in daytime and during summer while At night and during the winter the gradually cooling water This serves to moderate Evaporative Cooling Evaporation or vaporization is transformation of a Heat of vaporization is the heat a liquid must As a liquid evaporates its remaining surface cools substance from absorb for 1 g to through a temperatures in Evaporative cooling of water helps stabilize Figure 3 6 3 Floating of Ice on Liquid Water Water is less dense as a At 0 C water molecules are locked into The hydrogen bonds keep the molecules far enough apart to make the ice 10 Water reaches its greatest density at 4 C If ice sank all bodies of water would eventually freeze solid Physical States of Water Water unorganized Ice organized Many scientists are worried that global warming is having a profound effect on The rate at which glaciers and Arctic sea ice are disappearing poses an extreme challenge to animals that 4 Water The Solvent of Life A solution is a liquid that is a The solvent is the The solute is the An aqueous solution is one in which Table salt NaCl dissolving in water Solvent water H2O Solute salt NaCl Solution salty water Water is a versatile When an ionic compound is dissolved in water each ion is surrounded by a sphere of water molecules called Water can also dissolve compounds made of Even large polar molecules such as proteins can dissolve in water if they have Hydrophilic and Hydrophobic Substances A hydrophilic substance is one that has A hydrophobic substance is one that does Oil molecules are hydrophobic because they have Hydrophobic molecules related to oils are the Solute Concentration in Aqueous Solutions Most chemical reactions in organisms involve When carrying out experiments we use mass to calculate the number of solute molecules in Molecular mass is the sum of all masses of Numbers of molecules are usually measured in moles where 1 mole mol 6 02 1023 Avogadro s number and the unit dalton were defined such that 6 02 1023 daltons Molarity M is the number of moles of Possible Evolution of Life on Other Planets Biologists seeking life on other planets have focused their search on More than 800 planets have been found outside our solar system there is evidence that a few of them have In our solar system CONCEPT 3 3 Acidic and basic conditions affect living organisms A hydrogen atom in a hydrogen bond between two water molecules can The hydrogen atom leaves its electron behind and is transferred as a The molecule that lost the proton is The molecule with the extra proton is now a hydronium ion H3O though Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at Note that H does not exist on its own in an aqueous solution It is always associated with another Though statistically rare the dissociation of water molecules has a H and OH are Changes in their concentrations can drastically affect Concentrations of H and OH are Adding certain solutes called acids and bases modifies the Biologists use the pH scale to describe whether a solution is acidic or Here is a good link for pH information Acids and Bases An acid is a substance that increases the H A base is a substance that reduces the H Strong acids and bases Weak acids and bases reversibly release and accept back hydrogen ions but can still shift the balance of H and OH away The pH Scale In any aqueous solution at 25 C the product of H and OH is constant and can be written as H OH 10 14 The pH of a solution is defined by the negative logarithm of H concentration written as For a neutral aqueous solution H is 10 7 so pH log H pH 7 7 The pH scale ranges from In theory values less than 0 and greater than 14 are The pH Scale is Logarithmic 5 6 4 1 How many times MORE acidic more H ions is gastric juice than lemon juice 2 1 3 2 How many times MORE acidic more H ions is apple juice than coffee 3 How many times MORE acidic more H ions is milk than baking soda 4 How many times MORE acidic more H ions is baking soda than concentrated alkalis 5 How many times MORE basic more OH ions


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LSU BIOL 1201 - Water and Life

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