Ch. 3 Water and the Fitness of the Environment

3.1 The polarity of water molecules results in hydrogen bonding

Unequal sharingdue to

difference in electronegativity

Polar covalentbonds due to

unequal sharingof electrons

Polar nature ofwater due to polar

covalent bonds

H bonding due to polarnature of water

Hydrogen bonds between water molecules

3.2 Four emergent properties of water contribute to Earth’s fitness for life

1. Cohesion – water to water

- contributes to transport of water and dissolved nutrients against the force of gravity(benefit to life)

- surface tension(btl)

http://www.marcelapineros.com/_portfolio/surface/media/en_tension.swf

Transpiration

Figure 3.4

Adhesion

- Water clinging to a substance other than water

2. Moderation of Temperature

A) Heat and Temperature

• Ability to resist changes in temperature

• Heat vs temperature – measure of the matter’s total kinetic energy vs the average kinetic energy of the molecules

• Coffee pot vs swimming pool – same temperature….which has more heat???

• Calorie, kilocalorie, joule – see p. 48

B) High Specific Heat

• Amount of heat required to raise 1g of a substance 1degree Celsius

Ex) water = 1cal

ethyl alcohol = 0.6 cal

- can be traced to hydrogen bonding

- Absorb heat bonds break

- Bonds form heat is released

Benefit to life

• Limits fluctuation of temperature on land and in water

• Organisms able to resist changes in their own temperature

C) Evaporative Cooling

• vaporization/evaporation• Heat of vaporization – amount of heat a liquid

must absorb for 1 g of it to go from liquid to gas• Contributes to stability of temperature in lakes

and ponds• Prevents over heating in terrestrial organisms• Properties of Water

Is this molecule hydrophilic or hydrophobic?

pH

1. The H+ ion concentration of a solution can be represented as its pH value. The pH of a solution is defined as the negative log10 of the hydrogen ion concentration. What is the pH of pure water?

2. The COOH group in the acetic acid molecule from the previous slide can ionize to release a H+ ion into solution. If you add acetic acid to water and raise the concentration of H+ ions to 10-4, what is the pH of this solution?

Properties of water review

1. During the winter, air temperatures in the northern United States can remain below Oo C for months; however, the fish and other animals living in the lakes survive.

2. Many substances – for example, salt(NaCl) and sucrose – dissolve quickly in water.

3. When you pour water into a 25-ml graduated cylinder, a meniscus forms at the top of the water column.

4. Sweating and the evaporation of sweat from the body surface help reduce a human’s body temperature.

Properties of water review(con’t)

5. A bottle contains a liquid mixture of equal parts water and mineral oil. You shake the bottle vigorously and then set it on the table. Although the law of entropy favors randomness, this mixture separates into layers of oil over water.

6. Water drops that fall on a surface tend to form rounded drops or beads.

7. Water drops that fall on your car tend to bead or round up more after you polish(or wax) the car than before you polished it.

8. If you touch the edge of a paper towel to a drop of colored water, the water will move up into(or be absorbed by) the towel