Water and Buffers

Amazing Water!!!

• Cohesion

• Surface Tension

• Adhesion

• High Specific Heat

• High Heat of Vaporization

• Density

• Universal Solvent

Interaction Between Water Molecules

Negative Oxygen end of one water molecule is attracted to the Positive Hydrogen end of another water molecule to form a

HYDROGEN BOND

Cohesion

• Water molecules sticking to each other

• Hydrogen bonding between individual water molecules

• Constantly forming and breaking

• Transpiration in plants, surface tension,…

Surface Tension

• Measure of how difficult it is to stretch or break the surface of a liquid

• Important to “water striders”

• Important in your lungs

Adhesion

• The clinging of one substance to another

• Water sticking to glass• water clinging to the

sides of the xylem in plants helps to counter gravity

Adhesion Causes Capillary Action

• Gives water the ability to “climb” structures

• Diameter of tube vs. height?• Combined with cohesion =

High Specific Heat

• The amount of heat required to change 1g of a substance 1oc.

• Water will change its temp less when absorbing or losing a given amount of heat

• Land near large water bodies have milder climates than inland regions

• Water resists dramatic changes

• Internal body temps remain constant

High Heat of Vaporization

Heat of Vaporization

• 580 cal for 1g of H2O• Evaporation from leaves

keeps plant tissues from overheating

• A panting wolf rids its body of 540 calories of heat energy with each gram of water vapor exhaled.

• H2O’s high heat of vaporization helps moderate Earth’s temp.

Quantity of heat a liquid must absorb for 1g of it to be converted from liquid to gas

Santa Barbara 73°

Los Angeles(Airport) 75°

Pacific Ocean 68°

Santa Ana 84°

Burbank90°

San Bernardino100°

Palm Springs106°

Riverside 96°

San Diego 72° 40 miles

70s (°F)

80s

90s

100s

Density of Water

• At “normal” temps, water acts like anything else

• Kinetic Theory of Matter

• Gets interesting around 4°C

Density of Water

• As H2O cools the molecules slip closer together down to 40C

• At 0oC water becomes locked in a crystalline lattice

• The H-bonds keep the molecules farther apart than expected

• Ice floats, insulates the water below

Fall/Spring Overturns

Water is Less Dense as a Solid•Which is ice and which is water?Which is ice and which is water?

Water, the Universal Solvent

• Due to the polar nature of H2O

• Dissolves– Polar substances—

alcohol, sugar

– Ionic substances—salt, baking soda

pH Scale

• A measure of the H+ concentration in solution, defined as pH = - log H+

• Each pH unit is a tenfold difference in H+ or OH-.

• Biological systems between 6 – 8

• Blood 7.4

Buffers

• Substances that resist changes in pH when acids or bases are added.

• Produced naturally by the body to maintain homeostasis

• Bicarbonate buffer in human body maintains blood pH around 7.4

Quick Quiz

Quick Quiz1.Draw a water molecule with labeled atoms and charges.

2.What is the property called that describes water sticking to itself?

3.What makes a solution acidic?

4.What has a higher pH, ammonia or lemon juice?

5.Why do we sweat?

Quick Quiz1.Draw a water molecule with labeled atoms and charges.

Quick Quiz1.Draw a water molecule with labeled atoms and charges.

2.What is the property called that describes water sticking to itself?

Quick Quiz1.Draw a water molecule with labeled atoms and charges.

2.What is the property called that describes water sticking to itself?

3.What makes a solution acidic?

Quick Quiz1.Draw a water molecule with labeled atoms and charges.

2.What is the property called that describes water sticking to itself?

3.What makes a solution acidic?

4.What has a higher pH, bleach or lemon juice?

Quick Quiz1.Draw a water molecule with labeled atoms and charges.

2.What is the property called that describes water sticking to itself?

3.What makes a solution acidic?

4.What has a higher pH, bleach or lemon juice?

5.Why do we sweat?