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Water

Water. essential for life (as we know it!) any other chemical with this low of a molecular weight = GAS (but it’s a liquid at room temp!) b/c of it’s polarity, it tends to stick to itself COHESION b/c of it’s polarity, it tends to stick to other stuff ADHESION. Temperature.

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Water

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  1. Water • essential for life (as we know it!) • any other chemical with this low of a molecular weight = GAS (but it’s a liquid at room temp!) • b/c of it’s polarity, it tends to stick to itself COHESION b/c of it’s polarity, it tends to stick to other stuff ADHESION

  2. Temperature • b/c H2O molecules are so strongly attracted to each other, it requires quite a bit of heat to disrupt those bonds •  H2O can absorb a lot of heat and the temperature doesn’t change too much • converse is true as well • moderates temperature on land • moderates temperature in your body • sweating fever

  3. Cohesion • b/c of H+ bonds, H20 has a HIGH surface tension • water striders

  4. Adhesion • b/c of H+ bonds, H20 has a HIGH surface tension • meniscus in glass containers http://www.chemistryland.com/CHM151W/04-Solutions/liquids/meniscus.jpg

  5. States of Matter • solid: electrons moving slowly • liquid: electrons moving faster • gas: electrons moving FAST!! • usually when a substance solidifies, it shrinks: the atoms move more closely together • NOT H2O: expands b/c H bonds form rigid structure holding each molecule apart

  6. so? • b/c of this, solid H2O (aka. ice) is less dense than liquid H2O • so? • floats on top of body of water (prevents them from freezing solid-insulation) • pop can explodes in freezer (you’re in trouble now!)

  7. Like dissolves Like • polar substances dissolve in polar solvents means they get shells of hydration! • Solution = solute + solution • in us, solution = H2O • non-polar substances DO NOT dissolve in polar solvents

  8. Forms shells of hydration! http://web.virginia.edu/Heidi/chapter2/chp2.htm

  9. pH • water is constantly moving; a certain percentage of those molecules break up • ions are formed: • H+ • OH- • have equal amounts of each type of ion • some compounds release only H+ • some compounds release only ions that can accept H+ (negatively charged)

  10. pH • ACID: compound that releases H+ • strong: throw it in H2O and it dissolves completely • weak: throw it in H2O, some dissolves, some doesn’t • BASE: compound that accepts H+ • strong: throw it in H2O and it dissolves completely • weak: throw it in H2O, some dissolves, some doesn’t • p = -log of • H = hydrogen

  11. pH • pH scale tells you number of H+ ions present • pH = 0 (pure H+) • pH = 1 (10 x fewer H+) • pH = 2 (10 x fewer H+) • b/c pH = -log, you get stronger (more H+ ions) as the number gets lower

  12. Figure 2.14_1 pH scale Battery acid Lemon juice,gastric juice Vinegar, cola Increasingly ACIDIC(Higher H concentration) Tomato juice Rainwater Human urine Saliva NEUTRAL[H][OH] Pure water

  13. pH • pH gets higher = fewer and fewer H+ • so pH of 14 = safe, right? • NO!! • 7 is neutral: = number of H+ and ion that can accept H+ • as you go up the scale, the amount of ions that can accept H+ increases (becomes basic or alkaline) (10 x diff. between each #)

  14. Figure 2.14_2 pH scale NEUTRAL[H][OH] Pure water Human blood,tears Seawater Increasingly BASIC(Higher OH concentration) Milk of magnesia Household ammonia Household bleach Oven cleaner

  15. Figure 2.14_3 Basicsolution Neutralsolution Acidicsolution

  16. Buffer: minimizes Δs in pH • buffers accept H+ when it is high • buffers donate H+ when it is low • keeps pH in a stable position • buffers in your blood keep you from dying when your body produces a lot of acids

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