Chapter 3

Explain the difference between a pH of 8 and a pH of 12 in terms of H + concentration.

The H+ concentration of a pH 12 is 100,000 times greater than that of a pH of 8.

Explain the buffering system that minimizes blood pH changes

The chemical equilibrium between carbonic acid and bicarbonate acts as a pH regulator, the reaction shifting from left or right as other processes in the solution add or remove hydrogen ions.

Is water polar or nonpolar?

polar

Discuss how CO2 emissions affect marine life and ecosystems.

CO2 dissolves in seawater creating carbonic acid, which lowers the pH of the ocean causing ocean acidification.

How many times more basic is a pH of 12 compared to a pH of 8?

10,000

How many times more acidic is a pH of 3 compared to a pH of 5?

100

How many hydrogen bonds can a single water molecule form?

4

How do buffers moderate pH change?

A buffer is a substance that minimizes changes in the concentration of H+ and OH- in a solution. It does so by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted.

Define a calorie.

A calorie is the amount of heat it takes to raise the temperature of 1 g of water by 1°C, also the amount of heat that 1 g of water releases when it cools by 1°C.

Which property is demonstrated when you see beads of water on a waxed car hood?

Adhesion, water molecules attached to other water molecules to form a bead

Distinguish between hydrophobic and hydrophilic substances. Give an example of each.

Any substance that has an affinity for water is said to be hydrophilic, whereas substances that are nonionic and nonpolar and cannot form hydrogen bonds and therefore seem to repel water and are called hydrophobic.

Explain why ice floats. Why is 4°C the critical temperature?

As a result of hydrogen bonding, water expands as it solidifies. At 4°C water acts like other liquids, expanding as it warms and contracting as it cools. However, below 4°C water begins to freeze as more and more hydrogen molecules are moving to slowly to break the hydrogen bonds. Hydrogen bonds keep the molecules far enough apart to make ice about 10% less dense than water at 4°C; it is this lower density of ice that allows it to float.

Distinguish between cohesion and adhesion.

Cohesion is the hydrogen bonding that holds water molecules together while adhesion is an attraction between different substances

Define evaporation. What is heat of vaporization? Explain at least three effects of this property on living organisms.

Evaporation is the transformation of a liquid to a gas. The heat of vaporization is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state. The heat of vaporization accounts for the severity of steam burns, burns caused by the heat energy released when steam condenses into liquid on the skin.

Explain how hydrogen bonding contributes to water's high specific heat.

Heat is absorbed and released when hydrogen bonds form; therefore, a calorie of heat causes a relatively small change in the temperature of water because much of the heat is used to disrupt hydrogen bonds before water molecules can begin moving faster. Additionally, when the temperature of water drops slightly, many additional hydrogen bonds form, releasing a considerable amount of energy in the form of heat.

Which property explains the ability of a water strider to walk on water?

Surface tension

Consider what would happen if ponds and other bodies of water accumulated ice at the bottom. Describe why this property of water is important.

If ice sank, eventually ponds, lakes, and oceans would freeze solid and only a few inches at the top would thaw during the summer. Because ice floats, the upper frozen layer insulates the liquid water below, keeping it from freezing and allowing life to exist beneath the surface. Additionally, the frozen layer provides a solid habitat for some animals, such as polar bears and seals.

You already know that some materials, such as olive oil, will not dissolve in water. In fact, oil will float on top of water. Explain this property in terms of hydrogen bonding.

Oil molecules cannot form hydrogen bonds with water and thus behave hydrophobically, because there is a prevalence of relatively nonpolar covalent bonds—in this case, bonds between the carbon and hydrogen,which share electrons almost equally.

Explain why water is such a fine solvent.

The fact that water is such a versatile solvent can be traced back to the polarity of the water molecule. Watercan dissolve ionic compounds, many compounds made up of nonionic polar molecules, as well as molecules such as proteins if they have polar and ionic regions on their surface.

Water has high specific heat. What does this mean? How does water's specific heat compare to alcohol's specific heat?

The specific heat of a substance is defined as the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C. Water's specific heat is unusually high at 1 cal/g•°C, whereas alcohol's specific heat is is 0.6 cal/g•°C.

Summarize how water's high specific heat contributes to the moderation of temperature. How is this property important to life?

With a high specific heat, a large body of water can absorb and store a huge amount of heat from the sun in the daytime and during summer while warming up only a few degrees. As this water generally cools during the night and during winter, it warms the air, contributing to milder climates in coastal regions.

What two ions form when water dissociates?

hydronium (H3O+) and hydroxide ions (OH-)