AP Bio Quiz 2: Properties of Water

What is a polar molecule? Why is water considered polar?

The opposite ends have opposite charges.

Explain hydrogen bonding. How many hydrogen bonds can a single water molecule form?

Hydrogen bonds are weak bonds that are formed between electronegative portions of one atom and electropositive portions of another atom. Hydrogen bonds can form from one water molecule.

Cohesion

the attraction of water molecules to each other.

Adhesion

the attraction of water molecules to another substance.

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

Cohesion because the water molecules are attracted to each other and repel.

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

Surface tension- measure of how hard it is to break the surface of a liquid related to cohesion.

The calorie is a unit of heat. Define calorie.

The amount of heat required to raise the temperature of 1 g of water by one degree.

Water has high specific heat. What does this mean?

The heat that must be absorbed for 1g of that substance to change by 1C water's specific heat -

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

Heat is absorbed when hydrogen bonds break and a great deal of heat is required to break the hydrogen bonds in water when compared to alcohol.

How does water's specific heat compare to

alcohol's?

Water's= 1cal/g/C. Alcohol's = .58 cal/g/C/

What is released when hydrogen bonds are formed?

heat

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

It minimizes temperature fluctuations to allow for life on earth.

Define evaporation.

Transformation of water from a liquid to a gas.

Define Heat of vaporization.

heat that must be absorbed for 1g to be converted to a gas.

Explain at least three effects of heat of vaporization on living organisms.

1- Evaporative cooling. 2- stabilizes temperature in organisms. 3- stabilize temperatures of bodies of water.

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, all bodies of water would eventually freeze solid making life on earth impossible.

Now, explain why ice floats. Why is 4oC the critical temperature in this story?

Water is most dense at 4C; ice floats because the molecules become more ordered as a solid and are therefore less dense due to the crystalline structure.

Define solvent.

the dissolving agent of a solution- usually water.

Define solution.

homogenous mixture of substances in liquid form.

Define solute.

the substance that is dissolved in a solution.

Consider coffee to which you have added sugar. Which is the solvent? The solute?

Coffee is the solvent, the solute it the sugar.

Explain why water is such a fine solvent.

Because of its polarity allowing it to form hydrogen bonds easily.

Define hydrophilic.

Substance that does have an affinity for water.

Define hydrophobic.

non- polar- substance that does not have an affinity for water.

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.

Oils have non- polar bonds which do not bond with the polar Hydrogen bonds of water.

Define molarity.

The number of moles of solutes per liter of solution.

What two ions form when water dissociates?

hydronium- H3O+, H+ and hydroxide- OH-

Acid

Any substance that increases the H+ concentration of a solution.

base

Any substance that reduces the H+ concentration of a solution.

Buffer

substances that minimize changes in concentrations of H+ and OH- in solutions.

Explain the buffering system that minimizes blood pH changes.

blood contains a bicarbonate anion and a carbonic acid buffer to maintain a blood pH between 7.35 and 7.45

Acid precipitation is increasing. Explain its sources.

Fossil fuel contaminants combining with water in the air to form acids such as carbonic, nitric, and sulfuric acids.

Discuss how CO2 emissions affect marine life and ecosystems.

Leads to a decrease in the ability of corals to form calcified reefs.