Chapter Three: Water & The Fitness of the Environment

Question 1

What is a polar molecule? What is its relation with the properties of water?

Answer 1

A molecule with opposite charges on different ends of the molecule. It is the reason for water’s properties.

Question 2

What causes water to be fragile in liquid form? What are its four emergent properties?

Answer 2

Water is constantly re-forming hydrogen bonds with its neighbors. It hydrogen bonds to multiple partners (positive and negative parts attract). Four emergent properties are cohesion, moderation of temperature, expansion upon freezing, and it is the solvent of life.

Question 3

Cohesion v.s. Adhesion

Answer 3

Cohesion is the binding together of like molecules, often by hydrogen bonds. It contributes to the transport of water & dissolved nutrients against gravity in plants. Adhesion is the clinging of one substance to another. It helps counter the downward pull of gravity.

Question 4

Definition of Surface Tension

Answer 4

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a great surface tension.

Question 5

How can water moderate air temperature?

Answer 5

Water can moderate air temperature by absorbing heat from warmer air, & releasing it to cooler air. It absorbs/releases lots of heat with a light change in its temperature (it acts as a heat bank).

Question 6

What is kinetic energy? What is the difference between heat and temperature? What is the Celsius scale?

Answer 6

Kinetic energy is the energy of motion.
Heat is a form of energy; it is a measure of matter’s total kinetic energy and depends on the matter’s volume.
Temperature is a measure of heat intensity that represents the average kinetic energy of the molecules (no volume needed!). The Celsius scale is a temperature scale that measures the freezing & boiling point of water.

Question 7

Calorie v.s. kilocalorie v.s joule

Answer 7

Calorie: the amount of heat it takes to raise the temperature of 1 gram of water by 1 degree C.
Kilocalorie: the amount of heat required to raise the temperature of 1 kilogram of water by 1 degree C; 1 kcal = 1,000 cal
Joule: a unit of energy; 1 cal: 4.184 J 1 J = 0.239 cal

Question 8

What is specific heat?

Answer 8

Specific heat is the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by 1 degree C. Water has a high specific heat of 1 cal/g/C. When heat is released, hydrogen bonds form, when heat is absorbed, hydrogen bonds break. It keeps temperature fluctuations on land and in water within limits that permit life; organisms can resist changes in their temperature.

Question 9

Definition of heat of vaporization

Answer 9

The quantity of heat a liquid must absorb for one gram of it to be converted from liquid to gas. Hydrogen bonds must be broken to get to a gas.

Question 10

Definition of Evaporative Cooling

Answer 10

The process where an object becomes cooler during evaporation, owing to a change of the molecules with the greatest kinetic energy from liquid to gas. It proves stability of temperature in water and a mechanism that prevents terrestrial organisms from overheating.

Question 11

How does water expand instead of contracting when it solidifies?

Answer 11

Water is less dense as a solid than as a liquid. It begins to freeze when its molecules are no longer moving vigorously enough to break their hydrogen bonds. Its greatest density is at 4 degrees C. Hydrogen bonds are stable.

Question 12

What is the difference between a solution and an aqueous solution? Solvent v.s. Solute

Answer 12

Solution: a liquid that’s completely homogeneous mixture of at least two substances.
Aqueous solution: a solution where water is the solute
Solute: thing that’s dissolved
Solvent: dissolving agent

Question 13

Definition of hydration shell and colloid

Answer 13

the sphere of water molecules around a dissolved ion. Compounds both ionic and nonionic can dissolve in water
Colloid: a stable suspension of fine particles in a liquid

Question 14

Hydrophillic vs. hydrophobic

Answer 14

Hydrophillic: Any substance that’s attracted to water; some can’t dissolve
Hydrophobic: nonionic/nonpolar substances unable to form hydrogen bonds and repels water

Question 15

Definition of molecular mass

Answer 15

the sum of the masses of all the atoms in a molecule

Question 16

What is a mole (mol)? How is it related to molarity?

Answer 16

A mole is the number of grams of a substance that equals its molecular weight in daltons and contains Avogadro’s number of molecules. It’s always 6.02x10^23 (daltons in one gram). A mole of one substance has exactly the same number of molecules as a mole of any other substance.
Molarity: The number of moles of solute per liter of solution

Question 17

Explain the difference between an hydrogen ion, a hydroxide ion, and hydronium ion. Are they reactive? Do they have dynamic equilibrium?

Answer 17

Hydrogen atoms in a hydrogen bond can shift from one molecule to the other; it leaves its electrons behind
Hydrogen ion: a single proton with a charge of 1 +
Hydroxide ion: Water molecule that lost a proton (charge of 1 -)
Hydronium ion: H3O+
Yes and Yes

Question 18

Acid v.s. base

Answer 18

Acid: a substance that increases the hydrogen ion concentration of a solution (drops of +)
Base: a substance that reduces the hydrogen ion concentration of a solution (dissociates/accepts the H+)

Question 19

In an aqueous solution is the hydrogen ion concentration is 10^-2, what is the OH concentration?

Answer 19

10^-12

Question 20

Definition of PH

Answer 20

pH: the negative log of the hydrogen ion concentration. It declines as the hydrogen concentration rises

Question 21

What are buffers?

Answer 21

Buffers are substances that minimize changes in the concentrations of H+ and OH- in a solution. It accepts H+ in excess, and donates H+ in depletion.

Question 22

Definition of acid precipitation

Answer 22

Acid precipitation: rain, snow, or fog with a pH of below 5.2. Forests in the U.S. are still alive because of the Clean Air Act.