AP Biology 2007-2008

Water

The Molecule That Supports All Of Life

AP Biology

The Chemistry Of Water Water is a polar molecule

The atoms of water are held together by polar covalent bonds

Who wins? Oxygen(-)? Hydrogen(+)?

AP Biology

Noodle time!Do hydrogen bonds hold oxygenand hydrogen together IN water?

Pink – YesPurple – NoYellow – I’m not sure

AP Biology

Noodle time!What kind of bonds hold the hydrogen atoms to the oxygen atom in H2O?

Pink – Non-polar covalentPurple – HydrogenYellow – IonicGreen – Covalent

AP Biology

The Chemistry Of Water Molecules of water are held together by

Hydrogen bonds H+ of one water molecule attracted to O- of

another water molecule

AP Biology

The Properties Of Water (Super Powers)

1. Cohesion & Adhesion

2. Good Solvent

3. Low Density As A Solid

4. High Specific Heat

5. Heat Of Vaporization

6. Ionization of Water

I’m pretty super!

AP Biology

1.Cohesion

Try that with flour…or sugar…

Caused by the hydrogen bonds between H2O molecules

Makes water “sticky” Allows for this kid to drink out of his

straw And this guy to walk on water

AP Biology

1. Adhesion Caused by hydrogen bonding between

H20 and OTHER molecules Causes meniscus

AP Biology

Penny Challenge

AP Biology

TranspirationWater defies gravity and travels through plants from the roots up. Caused by COHESION & ADHESION!

AP Biology

2. Universal Solvent Solvents dissolve solutes creating solutions

The polarity of H2O makes it a good solvent

polar H2O molecules surround + & – ions pulling them apart

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Noodle Time Is any kind of liquid a good solvent? Let’s try it! A

B

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What do you notice?

AP Biology

Both A and B are POLAR.

Is C polar?

A

B

C

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What do you notice? A = polar B = polar C = ?

AP Biology

What dissolves in water? Hydrophilic

substances have attraction to H2Opolar or non-polar?

AP Biology

What doesn’t dissolve in water? Hydrophobic

substances that don’t have an attraction to H2O

polar or non-polar?

fat (triglycerol)

AP Biology

3. Low Density as a solid (Ice Ice Baby)

Most substances are more dense when they are solid, but

not water… Ice floats!

H bonds form a crystal

And this hasmade all the difference!

AP Biology

Water vs Ice – Use the Water Kits

AP Biology

Why is “ice floats” important? Oceans & lakes don’t freeze solid

surface ice insulates water below allowing life to survive the winter

if ice sank… ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw

seasonal turnover of lakes sinking cold H2O cycles nutrients in autumn

AP Biology

The Fireproof Balloon NOODLE TIME!

What will explode first?Pink - A balloon with H2OGreen - A balloon without H2O

Why did this happen?

AP Biology

4. High Specific Heat H2O resists changes in temperature

high specific heat takes a lot to heat it up takes a lot to cool it down

H2O moderates temperatures on Earth

AP Biology

5. Heat of vaporizationEvaporative cooling

Organisms rely on heat of vaporization to remove body heat

AP Biology

Alcohol vs. Water IN YO’ BODIES!

AP Biology

6. Ionization of water & pH Water ionizes

H+ splits off from H2O, leaving OH–

if [H+] = [-OH], solution is neutral if [H+] > [-OH], solution is acidic if [H+] < [-OH], solution is basic

pH scalehow acidic or basic a solution is1 7 14

H2O H+ + OH–H2O H+ + OH–

AP Biology

pH Scale10–1

H+ IonConcentration

Examples of Solutions

Stomach acid, Lemon juice

1

pH100 Hydrochloric acid0

10–2 2

10–3 Vinegar, cola, beer3

10–4 Tomatoes4

10–5 Black coffee, Rainwater5

10–6 Urine, Saliva6

10–7 Pure water, Blood7

10–8 Seawater8

10–9 Baking soda9

10–10 Great Salt Lake10

10–11 Household ammonia11

10–12 Household bleach12

10–13 Oven cleaner13

10–14 Sodium hydroxide14

tenfold changein H+ ions

pH1 pH210-1 10-2

10 times less H+

pH8 pH710-8 10-7

10 times more H+

pH10 pH810-10 10-8

100 times more H+

AP Biology

I’m pretty super!

Any questions?