Chapter 2 (Water) Flashcards
Water and Life
Water is the…
biological medium on Earth
Reactions, etc. happen in water
Cell weight is…water?
75%
Water has an…charge distribution
unequal
Each water molecule can form up to four hydrogen bonds with other water molecules
What are the three physical states of matter?
Solid
Liquid
Gas
What type of bonds is found in water?
Polar covalent bonds
The uneven distribution of charge on the molecule facilitates Hydrogen Bonding
Hydrogen Bonds in water is about…the strength of a covalent bond
1/20
Four Properties of Water Facilitate Life
- Highly cohesive and adhesive
- Temperature moderation
- Low density of ice
- Ability to dissolve other substances
Cohesion of Water Molecules
Water evaporates from top of tree
Pulls water upward from roots
Special cells transport water up the tree
Xylem
The adhesion of water to the cell wall and cohesion to other water molecules helps resist the pull of gravity
Surface Tension
Measure of how hard it is to break the surface of a liquid
Water has unusually high surface tension due to hydrogen bonding between the molecules at the air-water interface and to the water below
Temperature Moderation
Evaporation is transformation of a substance from liquid to gas
Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas
As a liquid evaporates, its remaining surface cools, a process called evaporative cooling
Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water
Floating of Ice on Water
Ice is less dense than water
Ice floats in liquid water because hydrogen bonds in ice are more “ordered” making ice less dense than water
Water is the…of life
solvent
Water is a polar solvent
Solution
Liquid that is a completely homogeneous mixture of substances
Solvent
The dissolving agent of a solution
Water is a polar solvent
Solute
The substance that is dissolved
Aqueous Solution
One in which water is the solvent
Water is a polar solvent
Unequal charge distribution allows it to dissolve many ionic compounds
Positive region of water molecules surround negative ions
Negative regions surround positive ions
Hydrophilic and Hydrophobic Substances
A hydrophilic substance is one that has an affinity for water
Tend to be polar or have polar covalent bonds
Salt and sugar
A hydrophobic substance is one that does not have an affinity for water
Are non-polar
Oils and fats
Buffers
Substances that minimize changes in concentrations of H+ and OH- in a solution
The internal pH of most living cells must remain close to pH 7
Most buffer solutions contain a weak acid and its corresponding base, which combine reversibly with H+ ions
