Chapter 3: water!

1. Water’s polarity results in Hydrogen bonding

• H bond: attraction b/t an O (or N) on one molecule, and an H on a DIFFERENT molecule– Weak, temporary

• When they break (e.g.

boiling water): is energy absorbed, or produced?

• What happens to energy when they form (i.e. condensation)

2. H2O can make 4 H bonds

• More than most liquids

• TO DO: diagram a water molecule

• From http://nrich.maths.org/7273

3. Surface tension

• Liquid mountaineering – a method of running ON water but not sinking in.

• From http://www.youtube.com/watch?v=Oe3St1GgoHQ

4. thermal, cohesive and solvent properties of water

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cohesion – H bonds!

Surface tension Ice floats

High heat capacity

High heat of vaporization

5. Cohesion: H2O’s stick together

• b/c water makes MORE H bonds (4) than most liquids

6. Water makes so many H bonds (4). Result: properties….

Property of water

Description & importance to life

How H bonds make it work

Surface tension

High Heat of vapor-ization

High specific heat

Ice floats Oceans don’t freeze solid

7. Water moderates temperature – high specific heat capacity (define – p. 48)

San Diego 72°

40 miles

Pacific Ocean

70s (°F)

80s

90s

100s

Santa Barbara 73°

Los Angeles (Airport) 75°

Burbank90°

San Bernardino100°

Riverside 96°Santa Ana 84° Palm Springs

106°

8. Water is a Solvent, so is a medium for chemical reactions

• Video clip: “water dissolves salt”.

• What part of the water molecule dissolves Na+? What part dissolves CL- ?

9. 3D animation of ice & water• 1. Go to:

http://www.edinformatics.com/interactive_molecules/water.htm

– Go thru the “water” lesson, • Q #1: why is water a good

solvent?• 2. Click on “water molecule”

below the model, scroll to “water is highly cohesive”, and click on “Click here or on the image to your left to view…”

• Q #2: what does the movie show you about H bonds?

– Mac users: for “right click”, hold down Control key & click.

– Click on “style”, then “Scheme”, then “CPK spacefill”, or “Label” etc.

10. ice• Click on “Ice” in the right

column.• Q #3: why does ice float? To

answer this:– Do the “Try this” for ice (“CPK

spacefill” etc.) then for waterQ #4: Write down the differences you see between liquid water and ice.

• Q #5: how many H bonds does a liquid water molecule make? How about an ice water molecule?

• Go back and answer question 3 now.

11. Practice

• In groups, figure out how to model the properties of water, referring to H bonds.

• One narrator, other actors

• Solvent: one NaCl, 3 water molecules, narrator

• Evaporative Cooling: one hot animal, 4 water mol’s, 1 narrator

• Ice formation: 4 waters, 1 narrator

• Transport: wall is plant vessel (xylem), 3 waters, 1 Mg++, 1 narrator. Show movement, adhesion, cohesion, transport of Mg++.

12. Acids & Bases

• ISSUE: pH of living tissue must be close to pH 7 (your blood is between 7.2 and 7.4)

• Acids: hi [H+]– ___ pH (“hi” or “lo”)

• Bases: lo [H+]– ___ pH

Assessment

• 1. explain how the polarity of the water molecule is important in evaporative cooling;

• Key:– 1. 4 H bonds by each H2O– 2. body heat breaks H bonds

of sweat– 3.