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Water and life

Water and life. A primer in emergent properties. Forms of water. Properties of water: polarity. Hydrogen bonds hold water molecules together Can form hydrogen binds with other polar molecules Bonds are weak and short-lived, but there are lots of them “hold” water in liquid form

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Water and life

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  1. Water and life A primer in emergent properties

  2. Forms of water

  3. Properties of water: polarity • Hydrogen bonds hold water molecules together • Can form hydrogen binds with other polar molecules • Bonds are weak and short-lived, but there are lots of them • “hold” water in liquid form • Contribute to surface tension

  4. Properties of water: cohesion • Water molecules are attracted to other polar molecules • Held together by hydrogen bonds • Water is drawn to charged surfaces (adhesion) • Surface tension makes water surface more difficult to break

  5. Properties of water: moderation of temperature • High specific heat • Property of polar substances • Water has more specific heat than most substances • Remains liquid within a wide range of temperatures • High heat of vaporization • Much energy required to break hydrogen bonds • Evaporation of water has cooling effect

  6. Heat, specific heat, and temperature • Heat-total kinetic energy of molecules; is volume dependent • Temperature: average kinetic energy • Heat passes from warmer to cooler environment • Calorie: amount of heat to raise the temperature of 1 gram of water 1oC Specific heat: amount of heat absorbed or lost when temperature of 1 g of water is changed by 1oC

  7. The moderating effect of the high specific heat of water

  8. Evaporative cooling • High specific heat: water can store a lot of heat • Heat of vaporization: 580 cal of heat required to vaporize 1 gram of water at 25oC • Evaporative cooling: energy “escapes” water in the form of vapor (gas)

  9. Water expands upon freezing • Ice is less dense than water • Bodies of water don’t freeze solid • Good news for organisms living in it!

  10. Water is the solvent of life • Water molecules form hydration spheres around polar or charged molecules • Water is the solvent • The substance is the solute • Polar molecules are hydrophilic • Nonpolar molecules are hydrophobic

  11. What is an aqueous solution? • Cell is an aqueous environment (solutes are dissolved in water) • Concentration of solutes can be calculated • Molecular mass of a molecule • 6.02 X 1023 molecules per mole • Mole of NaCl is 59.5 g; mole of glucose is 180 g • Overall solute concentration in cells is approx. 0.3 M

  12. Water can form ions • Water molecules can form ions: H3O+ and OH- • In pure water, [10-7M] of each • Acids increase [H+] • Bases decrease [H+] • Strong acids and bases dissociate completely in water • Weak acids and bases form reversible reactions

  13. The pH scale and its significance

  14. Buffers minimize pH changes • No matter the environment, pH inside cells is near neutral • Internal environment is constantly changing • Buffers act by adjusting pH changes back to neutral (how?) • Carbonic acid and bicarbonate acid act as a biological buffer system H2CO3 HCO3- + H+

  15. Fossil fuels, acidification, and the environment • Acidification of ocean reduces available CO32- for formation of calcium carbonate • “Acid rain” can be formed from emissions from fossil fuels

  16. Summary: water is essential for life on Earth • Hydrogen bonding between water molecules is the basis for water’s properties • Cohesion; specific heat; structure of ice; solvent function • The formation of acids and bases affects living things (which have ways to modulate those reactions)

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