230 likes | 571 Vues
Chapter 3: Water and Life. WATER. Objectives. Importance of H bonds to properties of water 4 unique properties of water Interpreting a pH scale Importance of buffers in biological systems. Structure of Water. Structure key to special properties Structure dictates function Polarity
E N D
Objectives • Importance of H bonds to properties of water • 4 unique properties of water • Interpreting a pH scale • Importance of buffers in biological systems
Structure of Water • Structure key to special properties • Structure dictates function • Polarity • Hydrogen bonding • Each molecule can form max 4
Fig. 3-2 – Hydrogen bond + H —— O – —— + H + – – +
4 Properties of Water • Cohesion • Moderation of temperature • Ice floats on liquid water • Water as a solvent
Properties of Water: Cohesive Behavior • Cohesion • Water linked to water • Responsible for surface tension • Partial charges make water “sticky” • Adhesion • Clinging of one substance to another • Transpiration • Water moves through xylem to open stomata • What roles do cohesion and adhesion play ? • How does polarity of water contribute to its cohesive and adhesive properties?
Fig. 3-3 Adhesion Water-conducting cells Direction of water movement Cohesion 150 µm
Concept Check • How does polarity of water contribute to its cohesive and adhesive properties? • How might Rainex alter the properties of glass to allow it to shed water. • Discuss with a partner then we will discuss as a class.
Properties of Water: Ability to moderate Temperature • 2. Moderation of temperature • Specific heat: amount of heat required to change 1g of substance 1 degree C • Water has very high specific heat • Implications to earths climate • Oceans • Organisms • Heat of vaporization: amount of heat to convert 1g of liquid to gas • Water has high heat of vaporization
Evaporative cooling • Evaporation is transformation of a substance from liquid to gas • As a liquid evaporates, its remaining surface cools, a process called evaporative cooling • Evaporative cooling helps stabilize temperatures in organisms and bodies of water
Specific Heat • Water’s high specific heat can be traced to hydrogen bonding • Heat is absorbed when hydrogen bonds break • Heat is released when hydrogen bonds form • The high specific heat of water minimizes temperature fluctuations to within limits that permit life
Properties of Water: Expansion Upon Freezing • 3. Ice insulates large bodies of water • Ice floats • Moderates temps by not allowing large bodies of water to freeze solid • What are affects on pond life? • 104.5 bond angle
Fig. 3-6a Hydrogen bond Liquid water Hydrogen bonds break and re-form Ice Hydrogen bonds are stable
Properties of Water: Versatility as a Solvent • 4. Water as a solvent • Solvent • Solute • Solution • Hydrophobic substances • Hydrophilic substances • Sphere of hydration
Fig. 3-8bc (b) Lysozyme molecule (purple) in an aqueous environment (c) Ionic and polar regions on the protein’s surface attract water molecules.
Deriving pH equation • 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 pH = –log [H+] • For a neutral aqueous solution [H+] is 10–7 = –(–7) = 7
Fig. 3-UN2 H H H O O O O H H H H H 2H2O Hydroxide ion (OH–) Hydronium ion (H3O+)
Acids & Bases • Acids and bases alter [H+] • pH of pure water is 7 • How does HCl increase the acidity ? • Increase [H] • How does NaOH decrease acidity ? • Decrease [H] • direct bases NH3 gas • Indirect NaOH
Fig. 3-9 pH Scale 0 1 Battery acid Gastric juice, lemon juice 2 H+ H+ H+ Vinegar, beer, wine, cola OH– 3 H+ H+ OH– Increasingly Acidic [H+] > [OH–] H+ H+ H+ 4 Tomato juice Acidic solution Black coffee 5 Rainwater 6 Urine OH– Saliva OH– Neutral [H+] = [OH–] 7 Pure water OH– H+ H+ OH– OH– Human blood, tears H+ H+ H+ 8 Seawater Neutral solution 9 10 Increasingly Basic [H+] < [OH–] Milk of magnesia OH– OH– 11 OH– H+ OH– Household ammonia OH– OH– OH– H+ 12 Basic solution Household bleach 13 Oven cleaner 14
Importance of Buffers to Biological Systems • Carbonic acid and hyperventilation • Rapid breathing • Blood CO2 concentration decreases • Blood carbonic acid levels decrease • Blood pH changes from normal • Adverse physiological effects • Dizziness • Visual impairment • Fainting • Seizures • Death
Acids and Bases • pH scale • pH = –log [H+] • 0-14 • Lower more acidic < 7 • Higher more basic > 7 • Acids: Excess H+ ions • Bases: Excess OH- • Pure water is neutral • Buffers: minimize changes in pH • Can accept or give H+ ions when needed • Carbonic Acid (H2CO3) moderates pH changes in blood plasma and in the ocean
Summary and Review • List and explain the four properties of water that emerge as a result of its ability to form hydrogen bonds • Distinguish between the following sets of terms: hydrophobic and hydrophilic substances; a solute, a solvent, and a solution • Define acid, base, and pH • Explain how buffers work