Henry Lin
Chapter 3: Water and the Fitness of the Environment
3.1 Polarity of water
A. H ends of water molecules attach themselves to O
of another H2O molecule
B. Hydrogen bond
C. New bonds continuously form, but it keeps the
water molecules together
part
Concept Check
1. What is electronegativity, and how does it affect
interactions between water molecules?
It is how positive or negative an atom is as a cause of being bonded together. Electrons from an
atom with a weaker electronegativity will move into the orbit of an atom with a higher
electronegativity, causing the first atom to become positive. This allows an atom with a negative
charge to easily bond with the positive atom.
2. Why is it unlikely that two neighboring water molecules would be arranged like this?
The 4 hydrogen atoms are positive, causing the two molecules to repel one another.
3. What would be the effect of the properties of the water molecule if oxygen and hydrogen had
equal electronegativity?
The molecules will lose their intramolecular ability to bond.
3.2 Four emergent properties of water contribute to Earth’s fitness for life
A. Cohesion
a. The substance is held together with the hydrogen bonds
b. With cohesion, water from the roots of a tree is “connected” to the water at the
leaves
c. Adhesion allows the water to hold together with another substance
B. Moderation of Temperature
a. A calorie is the amount of heat to raise the temperature of 1 g of water by 1 °C
b. One joule = .0239 calories; One calorie = 4.184 J
c. Specific heat of water allows organisms to retain their temperature
d. Large body of water could absorb heat in the summer but won’t lose it as rapidly
in the winter.
e. Evaporative cooling: When water evaporates on a surface, the surface isn’t as
hot
C. Solvents
a. Liquid that is a completely homogeneous mixture of two or more substances is
called a solution
b. Dissolving agent is solvent
c. Substance dissolved is solute
d. Aqueous solution: water is the solvent
e. When an ionic compound is the solute, the sphere around each dissolved ion is
called the hydration shell
f. Any substance that has an affinity for water: hydrophilic
g. Colloid: Stable suspension of fine particles in a liquid
h. Any substance that repels water: hydrophobic
i. Molarity: Number of moles per liter of solution
Concept Check
1. Describe how properties of water contribute to the upward movement of water in a tree.
The hydrogen bonds allow a “chain” of water molecules to connect together, so the force by the
roots will translate up the chain, up the tree.
2. Explain the saying “It’s not the heat; it’s the humidity.”
Since water has a high specific heat, the water keeps the heat it took for it to evaporate, heating
up the area around it.
3. How can the freezing of water crack boulders?
The water seeps into the rock. When the water freezes, the water expands and breaks the boulder
4. If you were a pharmacist, how would you make a 0.5- molar solution of sodium chloride?
5 A water strider’s legs are coated with a hydrophobic substance. What might be the benefit.
What would happen if the substance were hydrophilic?
It allows its feet to be able to repel the water so it could stand on it. If the legs were hydrophilic,
then the bug will be attracted into the water, not letting it stand.
3.3 pH
A. When a solute is added to a water solvent, either a
H+ or OH- is removed from the solute
B. Solutions with higher concentration of OH- than H+
are basic, and higher H+ are acidic
C. pH goes down = acid, pH goes up = basic
D. The pH scale goes by powers of 10
Concept Questions
1. Compared with a basic solution at pH 9, the same
volume of an acidic solution at pH 4 has 105 times as many
hydrogen ions
2. HCl is a strong acid that dissociates in water:
HCl  H+ + Cl-. What is the pH of 0.01 M HCl?
-log(10-2) = 2
3. Acetic acid (CH3COOH) can be a buffer, similar to
carbonic acid. Write the dissociating reaction, identifying
the acid, base, H+ acceptor, and H+ donor.
CH3COOH   CH3COO- + H+
CH3COOH is the acid, CH3COO- is the H+ acceptor,
CH3COOH is the hydrogen donor, and CH3COO- is the base
4. Given a liter of pure water and a liter solution of acetic acid, what would happen to the pH if
you added 0.01 mol of a strong acid to each? Use the reaction equation to explain the result.
pH of the water will become 7, and more CH3COOH will be made after the base CH3COOreacts with the acid’s hydrogen atoms.