Properties of water
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Properties of Water. Chapter 2. Water (H 2 O). Most important inorganic molecule in living things. Living organisms = 75-80% H 2 O. Many biological processes require H 2 O Survive 21-24 days without food Survive 3 days without water. Three Physical States of H 2 O. Solid (ice) Liquid

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Properties of Water

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Properties of Water

Chapter 2


Water (H2O)

  • Most important inorganic molecule in living things.

  • Living organisms = 75-80% H2O.

  • Many biological processes require H2O

    • Survive 21-24 days without food

    • Survive 3 days without water


Three Physical States of H2O

  • Solid (ice)

  • Liquid

  • Gas (vapor)


Properties of Water

  • Buoyancy

  • Polarity

  • Cohesion

  • Adhesion

  • Surface Tension

  • High Specific Heat

  • Forms solutions

  • Neutral pH


Heats Slowly & Cools Slowly

  • High Specific Heat- a lot of heat is needed to raise the temperature of 1 gram of H2O by 1°C

  • H2O retains heat & cools slowly.

    • Ex: pool/ocean is warm in the fall.

  • Allows organisms to maintain relatively constant body temperatures.


Polar Molecule

  • Atoms of different elements don’t always share e- equally.

    • More protons (+) in the nucleus means a stronger attraction for electrons (-).


Polar Molecule

  • e- drawn the nucleus with more protons MORE than the others.

    • Charges form  polar molecules or polar regions of large molecules


  • Cohesion- ability of H2O molecules to resist coming apart.

    • Keeps H2O molecules together as they move from roots to leaves.

Giant Sequoia


Cohesion and Surface Tension

  • How droplets of H2O form.

  • Attraction between H2O molecules  surface tension

    • Surface Tension- molecules in the surface layer are H-bonded to H2O molecules below them.

    • Prevents water’s surface from easily breaking.

Water Strider

Droplet Formation


Adhesion

  • Adhesion- attraction between H2O molecules and molecules of other substances (that can form H-Bonds).

    • Due to polarity of H2O

    • Other polar substances get wet (mix with H2O)

    • Nonpolar molecules, like oils, do not.


Adhesion and Capillary Action

  • Attraction of H2O to surfaces with a charge  capillary action

  • Capillary Action- tendency of liquids to rise in tubes of small diameter.

    • Explains movement of H2O from roots  leaves


Forms Solutions

  • Many substances dissolve in H2O.

  • Solution- mixture in which 1+ substances are evenly distributed in another substance.

    • Can be mixtures of liquids, solids, or gases.

    • Substances transported in organisms as solutions of water.

      • Ex: Plasma (liquid part of blood)- made up of various ions and macromolecules, as well as gases, that are dissolved in H2O.


Parts of Solutions

  • Solute- substance being dissolved.

    • Ex: Sugar

  • Solvent- substance in which solute is dissolved.

    • Ex: H2O

      Sugar + H2O  Sugar H2O

      **Sugar & H2O molecules remain unchanged and can be separated again.**


Low Density Solid

  • Ice (solid) is LESS dense than liquid H2O.


Acids and Bases

  • Bonds break between some water molecules as they collide.

    • Forms a H ion (H+) and a hydroxide ion (OH-).

      • Pure H2O ALWAYS has a low concentration of H+ and OH- ions

      • H+ ions = OH- ions


Acids and Bases

  • Compounds that form H+ when dissolved in H2O are acids.

    • Adding acids to pure H2O  H+ level increases above that of pure H2O

  • Bases- compounds that reduce [H+] in a solution.

    • Many bases form OH- when dissolved in H2O.

    • Lower [H+] because OH- reacts with H+ to form H2O.


Acids and Bases

  • pH scale- measures H+ concentration in a solution.


Acids and Bases

  • Each whole # (on pH scale) represents a factor of 10.

    • Solution with pH 5 has 10 times more H+ than a solution with pH 6.

    • Note: Stomach acid pH= 2 Blood pH= 7.5


Questions

  • Lemons have a pH of 2. Are lemons acidic or basic?

  • The strongest bases have a pH of ____.

  • Pure water is a neutral substance. What is the pH of pure water?


Animations/Tutorials/Videos

  • Matter: http://www.teachersdomain.org/asset/lsps07_int_naturematter/

  • Matter Video Review: http://www.teachersdomain.org/asset/psu06-nano_vid_matter/

  • Atomic Structure: http://www.teachersdomain.org/asset/lsps07_int_theatom/

  • Chemical Bonding: http://www.teachersdomain.org/asset/lsps07_int_chembonds/

  • Water Video: http://www.teachersdomain.org/asset/idptv11_vid_d4ksow/

  • NOVA Hunting the Elements Video: http://www.pbs.org/wgbh/nova/physics/hunting-elements.html


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