Slide 1 / 44 Chapter 3 Water and the Fitness of the Environment
Slide 2 / 44 Water: Supports All Life Water is the biological medium on Earth All 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 Water and Earth Three-quarters of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable
Slide 4 / 44 Hydrogen Bonding of water The polarity of water molecules results in hydrogen bonding - The water molecule is a polar molecule due to uneven distribution of electrons. The opposite ends of a water molecule have opposite charges. + +
Slide 5 / 44 Polarity The polarity of water molecules allows them to form hydrogen bonds with each other and contributes to the various properties water exhibits click here for an animation about water
Slide 6 / 44 1 In a single molecule of water, the two hydrogen atoms are bonded to a single oxygen atom by A hydrogen bonds. B nonpolar covalent bonds. C polar covalent bonds. D ionic bonds. E van der Waals interactions.
Slide 7 / 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 a covalent bond B a hydrogen bond C an ionic bond D a hydrophilic bond E a hydrophobic bond
Slide 8 / 44 Four properties of water All contribute to Earth’s fitness for life Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent
Slide 9 / 44 Cohesion Water molecules exhibit cohesion Cohesion is the bonding of a high percentage of the molecules to neighboring molecules Cohesion is due to hydrogen bonding
Slide 10 / 44 Cohesion and Adhesion Cohesion helps pull water up through the Water conducting cells microscopic vessels of plants Adhesion of water to plant cell walls also helps counteract the force of gravity 100 µ m 100 m m click here for a video on cohesion and adhesion
Slide 11 / 44 Surface Tension Surface tension is related to cohesion It is a measurement of how hard it is to break the surface of a liquid
Slide 12 / 44 3 What determines the cohesiveness of water molecules? A hydrophobic interactions B nonpolar covalent bonds C ionic bonds D hydrogen bonds E both A and C
Slide 13 / 44 4 Which of the following is possible due to the high surface tension of water? A Lakes don't freeze solid in winter, despite low temperatures. B A water strider can walk across the surface of a small pond. C Organisms resist temperature changes, although they give off heat due to chemical reactions. D Water can act as a solvent. E The pH of water remains exactly neutral.
Slide 14 / 44 5 What do cohesion, surface tension, and adhesion have in common with reference to water? A All increase when temperature increases. B All are produced by ionic bonding. C All are properties related to hydrogen bonding. D All have to do with nonpolar covalent bonds. E C and D only
Slide 15 / 44 Moderation of Temperature Water moderates air temperature by absorbing heat from warmer air and releasing the stored heat to cooler air. Water can absorb or release a large amount to heat with only a slight change in its own temperature.
Slide 16 / 44 Review: Heat and Temperature Kinetic energy is the energy of motion Heat is a measure of the total amount of kinetic energy due to molecular motion Temperature measures the intensity of heat due to average KE of molecules
Slide 17 / 44 Water’s High Specific Heat 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 1ºC.
Slide 18 / 44 Hydrogen Bonding and Specific Heat Water has a high specific heat, which allows it to minimize temperature fluctuations to within limits that permit life Heat must be absorbed in order to break hydrogen bonds Heat is released when hydrogen bonds form
Slide 19 / 44 Evaporation Evaporation is the transformation of a substance from a liquid to a gas Heat 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 20 / 44 Evaporative Cooling Evaporative cooling is a process in which as liquid evaporates, its remaining surface cools Evaporative cooling is due to water’s high heat of vaporization Evaporative cooling of water helps stabilize temperatures in living things and in bodies of water
Slide 21 / 44 6 Water's high specific heat is mainly a consequence of the A small size of the water molecules. B high specific heat of oxygen and hydrogen atoms. absorption and release of heat when hydrogen bonds C break and form. D fact that water is a poor heat conductor. E inability of water to dissipate heat into dry air.
Slide 22 / 44 Floating Ice The hydrogen bonds in ice are more “ordered” than in liquid water, making ice less dense, and able to float.
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 Lysozyme molecule in an nonaqueous environment. aqueous environment such as tears or saliva.
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? A ionic B hydrogen C covalent D A and C only E A, B, and C
Slide 26 / 44 Hydrophilic and Hydrophobic Substances A hydrophobic substance A hydrophilic substance does not have an affinity for has an affinity for water water
Slide 27 / 44 Solute Concentration in Aqueous Solutions Most biochemical reactions occur in water Therefore, it is important to learn to calculate the concentration of solutes in an aqueous solution
Slide 28 / 44 Aqueous Solutions Calculations A mole represents an exact number of molecules of a substance, 6.02 x 1023 Molarity is the number of moles of solute per liter of solution Concentrations of aqueous solutions may also be measured in mass percent, e.g. 10% salt solution
Slide 29 / 44 Dissociation of water Dissociation of water molecules leads to acidic and basic conditions that affect living organisms Water can dissociate into hydronium ions and hydroxide ions Changes in the concentration of these ions can have a great affect on living organisms
Slide 30 / 44 – + H H O H O H H H Hydronium Hydroxide ion (H 3 O + ) ion (OH – ) click here for an animation about hydrogen bonding
Slide 31 / 44 Effects of Changes in pH Concentrations of H + and OH - are equal in pure water Adding certain solutes, called acids and bases, modifies the concentrations of H + and OH - Biologists use the pH scale to describe how acidic or basic (or alkaline) a solution is
Slide 32 / 44 Acids and Bases H+ An acid is any substance that increases the hydrogen ion concentration of a solution. A base is any substance that OH- reduces the hydrogen ion concentration of a solution
Slide 33 / 44 The pH Scale The pH of a solution is determined by the relative concentration of hydrogen ions The pH of acids are low, below 7 The pH of bases are above 7 up to 14 Most biological fluids have pH values around 6-8
Slide 34 / 44 The pH Scale Increasingly [H+] > [OH–] Acidic The pH scale and pH values of various aqueous solutions Neutral [H+] = [OH–] Increasingly [H+] < [OH–] Basic
Slide 35 / 44 Buffers The internal pH of most living cells must remain close to pH 7 Buffers are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution They consist of an acid-base pair that reversibly combines with hydrogen ions
Slide 36 / 44 Acid Precipitation Acid precipitation refers to rain, snow, or fog with a pH lower than pH 5.6 Caused primarily by the mixing of different pollutants with water in the air
Slide 37 / 44 Acid Precipitation 0 More 1 acidic Acid precipitation 2 3 Acid can damage life in rain 4 Earth’s water and 5 Normal rain soil ecosystems, 6 7 such as lakes, streams and 8 9 forests 10 11 More 12 basic 13 14
Slide 38 / 44 8 A given solution contains 0.0001(10 -4 ) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution? A acidic: H+ acceptor B basic: H+ acceptor C acidic: H+ donor D basic: H+ donor E neutral
Slide 39 / 44 9 What would be the pH of a solution with a hydrogen ion [H + ] concentration of 10 -8 M? pH = - log [H + ] A pH 2 B pH 4 C pH 6 D pH 8 E pH 10
Slide 40 / 44 10 What would be the pH of a solution with a hydroxide ion [OH - ] concentration of 10 -12 M? K w = 10 -14 A pH 2 B pH 4 C pH 10 D pH 12 E pH 14
Slide 41 / 44 11 Which of the following solutions has the greatest concentration of hydrogen ions [H + ]? A gastric juice at pH 2 B vinegar at pH 3 C tomato juice at pH 4 D black coffee at pH 5 E household bleach at pH 12
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