Chapter 3: What’s so great about water? Copyright 2010 Scott A. Bowling Life as we know it requires water: all organisms mostly liquid water most metabolism requires aqueous (water) medium many organisms live in liquid water or in an environment dominated by water in its various states (solid, liquid, or gas) . Chapter 3: What’s so great about water? Copyright 2010 Scott A. Bowling Some numbers: cells are typically 70% or more water by mass about 75% of the Earth’s surface is covered by liquid water . Chapter 3: What’s so great about water? Copyright 2010 Scott A. Bowling Some numbers: cells are typically 70% or more water by mass about 75% of the Earth’s surface is covered by liquid water But then, just being common on the Earth doesn’t make something essential for life. A large percentage of the Earth’s crust is sand, but we don’t consider sand a requirement for life. . Chapter 3: What’s so great about water? Copyright 2010 Scott A. Bowling Some numbers: cells are typically 70% or more water by mass about 75% of the Earth’s surface is covered by liquid water But then, just being common on Earth doesn’t make something essential for life. A large percentage of the Earth’s crust is sand, but we don’t consider sand a requirement for life. What is it about water that makes it so special? . Copyright 2010 Scott A. Bowling Chapter 3: What’s so great about water? polar nature of water molecules What properties of water are important for life? Acids and Bases Some useful definitions . Copyright 2010 Scott A. Bowling Chapter 3: What’s so great about water? polar nature of water molecules What properties of water are important for life? Acids and Bases Some useful definitions . Copyright 2010 Scott A. Bowling • Draw a water molecule (structural formula) • Then draw in four more around it that are connected to it by hydrogen bonds. . polar nature of water molecules oxygen atoms are electron seeking (electronegative), especially compared to hydrogen; thus for an oxygen-hydrogen bond: Copyright 2010 Scott A. Bowling the oxygen atom has a partial (-) charge the hydrogen atoms have a partial (+) charge . Copyright 2010 Scott A. Bowling polar nature of water molecules the polar character of water allows water molecules to form up to 4 hydrogen bonds . Copyright 2010 Scott A. Bowling • Draw a water molecule (structural formula) • Then draw in four more around it that are connected to it by hydrogen bonds. . Copyright 2010 Scott A. Bowling Chapter 3: What’s so great about water? polar nature of water molecules What properties of water are important for life? Acids and Bases Some useful definitions . Copyright 2010 Scott A. Bowling • List and describe at least four properties of water that result from its polar nature/hydrogen bonds. • Describe how water acts as a temperature buffer (creates temperature stability). . What properties of water are important for life? all of this come in some way from water’s polar nature hydrogen bonds and similar interactions Copyright 2010 Scott A. Bowling water is the principal solvent in living things water exhibits both cohesive and adhesive forces water helps maintain a stable temperature ice (solid water) floats in liquid water . water is the principal solvent in living things Copyright 2010 Scott A. Bowling highly polar = excellent solvent for other polar substances, and for ionic compounds . Copyright 2010 Scott A. Bowling water is the principal solvent in living things hydrophilic substances – interact readily with water hydrophobic substances – do not interact readily with water nonpolar substances good components for membranes . Copyright 2010 Scott A. Bowling water exhibits both cohesive and adhesive forces cohesive forces: attraction of water molecules each other give water a high surface tension . water exhibits both cohesive and adhesive forces adhesive forces: water molecules to be attracted to other kinds of molecules Copyright 2010 Scott A. Bowling how things are made wet capillary action: water moving through narrow tubes even against gravity results from cohesion and adhesion living organisms take advantage of this . water helps maintain a stable temperature high specific heat of water temp. stability Copyright 2010 Scott A. Bowling specific heat – energy to raise the temp. of 1 gram of something 1ºC h-bonds make water specific heat high 1 calorie / gram ºC comparatively, takes more energy gain/loss to change water temp. . water helps maintain a stable temperature high specific heat of water temp. stability Copyright 2010 Scott A. Bowling much of the ecosphere is water most biological organisms >70% water temperature stability is critical for most life . water helps maintain a stable temperature high heat of vaporization of water helps cool the ecosphere and biological organisms Copyright 2010 Scott A. Bowling heat of vaporization: energy to move 1 gram from liquid to gas . water helps maintain a stable temperature high heat of vaporization of water helps cool the ecosphere and biological organisms Copyright 2010 Scott A. Bowling heat of vaporization: energy to move 1 gram from liquid to gas h-bonds make water specific heat high 540 calories / gram . water helps maintain a stable temperature high heat of vaporization of water helps cool the ecosphere and biological organisms Copyright 2010 Scott A. Bowling heat of vaporization: energy to move 1 gram from liquid to gas h-bonds make water specific heat high 540 calories / gram organisms use this for cooling examples: sweating; evaporative cooling of a leaf . Describe how water acts as a temperature buffer (creates temperature stability). Copyright 2010 Scott A. Bowling • . . Copyright 2010 Scott A. Bowling ice floats Copyright 2010 Scott A. Bowling liquid water becomes denser as it cools – but only up to a point . ice floats Copyright 2010 Scott A. Bowling liquid water becomes denser as it cools – but only up to a point at 4ºC: water begins to expand as it cools further – that is, it gets less dense from then on – due to hydrogen bonds becoming locked in place . Copyright 2010 Scott A. Bowling ice floats at 0ºC: ice freezes into a crystal . Copyright 2010 Scott A. Bowling ice floats at 0ºC: ice freezes into a crystal based on the hydrogen bonds . Copyright 2010 Scott A. Bowling ice floats at 0ºC: ice freezes into a crystal based on the hydrogen bonds floating ice keeps lakes, etc., from freezing solid and is important for temperature cycling on the planet . List and describe at least four properties of water that result from its polar nature/hydrogen bonds. Copyright 2010 Scott A. Bowling • . Copyright 2010 Scott A. Bowling Chapter 3: What’s so great about water? polar nature of water molecules What properties of water are important for life? Acids and Bases Some useful definitions . Copyright 2010 Scott A. Bowling • Define acids and bases. . Acids and Bases acids are proton donors Copyright 2010 Scott A. Bowling . Acids and Bases acids are proton donors Copyright 2010 Scott A. Bowling dissociates to yield hydrogen ions (H+) in solution HA (an acid) H+ + A- (an anion) . Acids and Bases acids are proton donors Copyright 2010 Scott A. Bowling dissociates to yield hydrogen ions (H+) in solution HA (an acid) H+ + A- (an anion) H+ = one proton (mostly) . Acids and Bases acids are proton donors Copyright 2010 Scott A. Bowling dissociates to yield hydrogen ions (H+) in solution HA (an acid) H+ + A- (an anion) H+ = one proton (mostly) when the atom loses its electron to become a hydrogen ion, all that remains is the nucleus . Acids and Bases acids are proton donors Copyright 2010 Scott A. Bowling dissociates to yield hydrogen ions (H+) in solution HA (an acid) H+ + A- (an anion) H+ = one proton (mostly) when the atom loses its electron to become a hydrogen ion, all that remains is the nucleus thus, hydrogen ions are sometimes referred to as protons . Acids and Bases acids are proton donors Copyright 2010 Scott A. Bowling dissociates to yield hydrogen ions (H+) in solution HA (an acid) H+ + A- (an anion) H+ = one proton (mostly) when the atom loses its electron to become a hydrogen ion, all that remains is the nucleus thus, hydrogen ions are sometimes referred to as protons therefore, any substance that yields a proton is an acid, or an acid is a proton donor . Acids and Bases bases are proton acceptors Copyright 2010 Scott A. Bowling a base is a substance that can accept a proton . Acids and Bases bases are proton acceptors Copyright 2010 Scott A. Bowling a base is a substance that can accept a proton bases either dissociate in water to produce hydroxide ions and a cation, or split water to form a cation and hydroxide ion: Na+ + OH- NaOH or B (a base) + HOH BH+ + OH- . Acids and Bases Copyright 2010 Scott A. Bowling water tends to slightly dissociate into hydrogen and hydroxide ions (H+ and OH-) HOH H+ + OH- . Acids and Bases water tends to slightly dissociate into hydrogen and hydroxide ions (H+ and OH-) Copyright 2010 Scott A. Bowling HOH H+ + OH- in pure water, the concentrations of these ions are equal: [H+] = [OH-] = 10-7 M (note that the designation M stands for molar, the moles of a substance per liter of solution) the product of these remains constant: [H+] x [OH-] = 10-14 acidic solutions have an elevated [H+], and thus reduced [OH-] basic solutions have an elevated [OH-], and thus reduced [H+] . Copyright 2010 Scott A. Bowling • Define acids and bases. . What does pH stand for, and how does the pH scale work? Copyright 2010 Scott A. Bowling • . Acids and Bases pH scale shorthand notation for proton concentration of a solution Copyright 2010 Scott A. Bowling the pH is -log[H+] pure water ( [H+]= 10-7 M ) has pH = 7 pH < 7 is acidic; pH > 7 is basic pH of most living cells is usually ~ 7.2 to 7.4 . What does pH stand for, and how does the pH scale work? Copyright 2010 Scott A. Bowling • . Copyright 2010 Scott A. Bowling • How do pH buffers work? . Acids and Bases buffers minimize pH changes Copyright 2010 Scott A. Bowling weak acids and weak bases serve as buffers living things use buffers to prevent dramatic changes in pH, which can kill them . Acids and Bases buffers minimize pH changes Copyright 2010 Scott A. Bowling weak acids and weak bases serve as buffers living things use buffers to prevent dramatic changes in pH, which can kill them . 02.20 Buffer Formation Slide number: 2 + H2O Water CO2 Carbon dioxide Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 02.20 Buffer Formation Slide number: 3 + H2O Water CO2 Carbon dioxide H2CO3 Carbonic acid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 02.20 Buffer Formation Slide number: 4 – + + H2O Water CO2 Carbon dioxide H2CO3 Carbonic acid HCO3– Bicarbonate ion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + H+ Hydrogen ion Fig. 2.19 Copyright 2010 Scott A. Bowling • How do pH buffers work? . Copyright 2010 Scott A. Bowling Chapter 3: What’s so great about water? polar nature of water molecules What properties of water are important for life? Acids and Bases Some useful definitions . Copyright 2010 Scott A. Bowling Some useful definitions solvent – a liquid into which a substance dissolves solute – the dissolved substance solution = solvent + solute salts – form from acids and bases water is formed the cation of the base and the anion of the acid form the salt HCl + NaOH NaCl + HOH . Some useful definitions electrolytes are salts, acids, or bases that form ions in water and thus can conduct an electrical current when dissolved in water (pure water is a poor conductor of electricity, but put in a salt and it becomes an excellent conductor) nonelectrolytes are substances like sugar that dissolve in water but do not become ionic mixtures - a mixture of 2 or more elements and/or compounds; they can be broken down into elements and compounds by simple physical means. There are two types: Copyright 2010 Scott A. Bowling heterogeneous mixtures - mixtures that are not of uniform composition throughout - a living organism is a good example homogeneous mixtures - mixtures that are completely uniform throughout - a salt water solution is a good example .
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