Biology Test I - Water

Front 1

Properties of Water

Back 1

1. Water is polar
2. Hydrogen bonds

Front 2

Why is water polar?

Back 2

- Oxygen is more electronegative than hydrogen
- Shared electrons spend more time around the oxygen (O slightly negative and H slightly positive)

Front 3

Properties of Water's hydrogen bonds

Back 3

- Charge attraction (H+ attracted to O-)
- Each water molecule can form a maximum of 4 hydrogen bonds

Front 4

Consequences of Water's Polarity

Back 4

A. Strong cohesive and adhesive properties
B. Moderates the temperature of the Earth
C. Oceans and lakes don't freeze from the bottom-up
D. Solvent properties

Front 5

Cohesion

Back 5

- H-bonds cause water molecules to stick together
- Upward transport of water in plants

Front 6

Adhesion

Back 6

H-bonds to vessel walls counteracts gravity
- Water has a high surface tension

Front 7

Ways Water moderates the temperature of the Earth

Back 7

1. Water stabilizes air temperatures
2. Evaporative cooling

Front 8

How does water stabilize air temperatures?

Back 8

- Absorbs heat from warmer air
- Releases heat to cooler air

Due to high specific heat: water can absorb or release relatively large amounts of heat with only a slight change in its own temperature

Front 9

Water resists changes in temperature (Yes/No)

Back 9

Yes.

Front 10

How does water have high specific heat?

Back 10

Hydrogen bonds:
- Heat must be absorbed to break hydrogen bonds
- Heat is released when hydrogen bonds form

Front 11

What is the result of water's high specific heat?

Back 11

A large body of water acts as a heat sink.
- it absorbs heat from the sun and releases it at night and during winter

Front 12

What is evaporative cooling?

Back 12

Liquid -> Gas
vaporization or evaporization

Front 13

Evaporative cooling is due to?

Back 13

High heat of vaporization (caused by H-bonds)

Front 14

Evaporative cooling moderates climate by:

Back 14

- absorbing heat in the tropics
- releasing heat when it rains

Front 15

Evaporative cooling moderates the temperature of animals:

Back 15

Liquid evaporates at the skin
- most energetic molecules leave
- lower kinetic molecules remain
- surface is cooler

Front 16

Why don't oceans and lakes freeze from the bottom-up?

Back 16

Water is less dense as a solid than as a liquid.

Front 17

Why is water less dense as a solid than as a liquid?

Back 17

Liquid water: H-bonds are continually breaking and forming (water molecules can get close together)
Ice: H-bonds no longer break and reform (water molecules are locked at a fixed distance)

Front 18

Ice is about how much lighter than liquid water?

Back 18

10% less dense

Front 19

Ice floats in liquid water (Yes/No)
Conclusion?

Back 19

Yes. This prevents deep bodies of water from freezing bottom-up.

Front 20

Solvent properties of water (define)

Back 20

Water is a versatile solvent
- due to its polarity
- forms hydrogen bonds with polar and charged covalent molecules (e.g. NaCl)
Water surrounds individual ions, separates and shields them from one another

Front 21

Hydrophilic (define)

Back 21

has an affinity for water
e.g. ionic and polar substances

Front 22

Hydrophobic (define)

Back 22

has no affinity for water
e.g. non-ionic and nonpolar

Thus, water cannot form H-bonds