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Water (H 2 O)

Water (H 2 O). Why water exists and why is it important Water’s unusual properties Hydrogen bonding and polarity Liquid state Cohesion Solvent Water and solutions Hierarchy theory and the emergent properties of water. Take Home Message.

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Water (H 2 O)

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  1. Water (H2O) • Why water exists and why is it important • Water’s unusual properties • Hydrogen bonding and polarity • Liquid state • Cohesion • Solvent • Water and solutions • Hierarchy theory and the emergent properties of water

  2. Take Home Message • Water is unique among all liquids and the uniqueness plays a major role in life on Earth and elsewhere in the solar system • Water’s unusual and unique properties give it a place “all its own” among compounds and molecules • Water solutions and pH are critical concepts in chemistry and biology • Emergent properties of H2O are a special case study of the significance of hierarchy theory

  3. Elements of the Solar System: Role in Living Systems • 25 of 92 natural elements are known to be essential to life on Earth • Four of the above make up 96% • Carbon (C), Oxygen (O),Hydrogen(H) and Nitrogen (N) • Compare to solar abundance and discuss relative to origin/evolution of life

  4. Elements of the Periodic Table

  5. Water and Its Properties: Composition • Elemental composition of H2O • Hydrogen is the most abundant element in universe • Oxygen is the 3rd most abundant element • Hypothesis: H2O is common throughout the universe

  6. Liquid Solution for Living Systems • Introduction • Life on Earth in water ~4 billion years ago • First 3 billions years of life in water alone • All life tied to watery medium (plants, animals and microbes) • Simplicity and complexity of the nature of the water molecule • Deceptively simple in structure • Exquisite in function

  7. Water and Its Properties: Polarity • Composition and structure: a polar molecule • Features • Attraction is electrical • Hydrogen bonding among two or more molecules of H2O • Exquisite properties of H2O arise from chemical attractions among molecules because H2O is a polar molecule

  8. Water and Its Properties: Polarity

  9. Water and Its Properties: Phase Diagram

  10. Water and Its Properties: Liquid State • Water is liquid over broad range of temperatures 0oC to 100oC • Comparison with other compounds CompoundChemical FormulaFreeze VaporRange(oC) (oC) (oC) Water H2O 0 100 100 Ammonia NH3 -78 -33 45 Methane CH4 -182 -164 18

  11. Water and Its Properties: Liquid State • Significance of broad range of temperatures for water to exist as a liquid • Water in a liquid state is not too cold to slow reactions and not too hot to break bonds • Could life evolve in another phase (i.e., gas, solid)?

  12. Water and Its Properties: Cohesion of Molecules • Cohesion: H2O molecules are “sticky” • Each hydrogen bond last 1 x 10-12 seconds • Constant formation and breakage of bonds: any moment, a substantial number of H2O molecules are bonded to its neighbors • Consequence: more structure than other liquids

  13. Water and Its Properties: Freezing • Water is unusual in that H2O is less dense as a solid than a liquid (it floats) • Mechanism • H2O expands when it solidifies • Due to hydrogen bonding • Consequence • Ponds, lakes and ocean freeze from the top down • Consequence for living system?

  14. Water and Its Properties: Freezing

  15. Water and Its Properties: Solvent of Life • Water is versatile solvent, due to its polarity and dissociation H2O H+ + OH- H2O + H+ H3O+ (hydronium ion) • In pure water, 1 molecule in every 554 million is dissociated (10-7 molar concentration)…pH scale • Statistically very rare BUT exceedingly important in chemistry of life (e.g., proteins, macromolecules) • H+ and OH- are very reactive and affect much of the chemistry of living systems (e.g., membranes, metabolism)

  16. Water and pH

  17. Water and Solutions • Solutions: mixture of ions or molecules of 2 or more substances • Air as a mixture (O2 in N2) • Tea as a mixture (aqueous if water)) • Coffee as a mixture (aqueous) • Solvent (majority) and solute (minority)

  18. Water and Solutions: Concentrations • Concentrations of solutes and solvents • Parts per million (ppm) or billion (ppb) • Atmosphere and carbon dioxide (370 ppm) • Percentage by mass • Salinity of ocean water - mass of salts in 1,000 grams of water (35 g in 1000 g water) • Chemistry: molarity of solution • # moles of solute dissolved in 1 liter of solvent (H2O)

  19. Water and Solutions: Concentrations • Moles • Little furry critters with no eyes that live in tunnels in the ground; 3 moles per acre is a 1 molar solution • Moles to a chemist are not furry animals • 1 mole is 1 gram molecular weight of a substance (atom, molecule), and it always contains the exact same number of atoms or molecules • 6.02 x 1023 atoms – Avogadro’s Number (not avocado) • 1 mole of C is 12 grams and it contains 6.02 x 1023 atoms • 1 mole of Na is 23 grams and it contains 6.02 x 1023 atoms • 1 mole of H2O is 18 grams and it contains 6.02 x 1023 molecules of H20 • Very precise way of measuring concentration

  20. Hierarchy Theory and Emergent Properties of H2O • Principle of hierarchy theory • Principle of emergent properties • Example of H2O in Periodic Table • a priori: combine one atom of O with two atoms of H • Emergent properties • Liquid • Hydrogen bonding and polarity • H+ and OH- in solution • Solvent • Range of temperature at which liquid • Three phases (gas, liquid and solid)

  21. Question Substance A has a pH of 2 and Substance B has a pH of 3. This means that ____. A. Substance A is more basic than Substance B B. Substance B is more acidic than Substance A C. Substance A is 10 times more acidic than substance B D. Substance B is 10 times more acidic than substance A

  22. Questions A deep lake in Minnesota is covered with ice. What is the water temperature at the bottom of the lake? In the summer in Virginia, pond water temperature is very warm (~30 0C). In the fall, the drop in night time air temperature results in surface water temperature falling (e.g., 20 0C). What would you expect to happen in small ponds as the surface water temperature is cooler than the water temperature at the bottom of the pond (~30 0C)?

  23. Question How does ocean water in proximity to continents affect the climate of the adjoining land mass? Explain your analysis based on the physical and chemical properties of water.

  24. Question In the search for life on other planets and in other solar systems, why is the presence and/or absence of water regarded as one of the cardinal indicators of the possibility of life?

  25. Take Home Message • Water is unique among all liquids and the uniqueness plays a major role in life on Earth and elsewhere in the solar system • Water’s unusual and unique properties gives it a place “all its own” among compounds and molecules • Water solutions and pH are critical concepts in chemistry and biology • Emergent properties of H2O are a special case study of the significance of hierarchy theory in the natural sciences

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