Biology Chapter 2 HW

Which property of water allows a water strider to walk on water?

water's high surface tension; Water's high surface tension, related to its cohesion, makes water behave as though coated with an invisible film.

Which of the following is a hydrophobic material?

wax

Why doesn't oil mix with water?

(c) Polar molecules attract one another. Water molecules cling to one another and won't part to make room for uncharged (nonpolar) molecules. There's no repulsion.

The amount of energy that must be absorbed or lost to raise or lower the temperature of 1 g of liquid water by 1°C _____.

is 1 calorie; The specific heat of liquid water is 1 cal/g/°C.

A pH of 6 is how many times more acidic than a pH of 9?

1,000; A pH of 6 is 10 times more acidic than 7, which is 10 times more acidic than 8, which is 10 times more acidic than 9. 10 x 10 x 10 = 1,000.

Select the statement that best describes a buffer.

A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added; In this fashion, buffers minimize the change in the pH of a solution.

Why isn't this insect drowning?

Surface tension; The high surface tension of water allows the insect to remain on the surface.

In this molecule, what type of bond is found between the oxygen and hydrogens?

polar covalent; While oxygen shares electrons with hydrogen, the electrons spend more time with the oxygen than with the hydrogens.

Electronegativity is

the attraction of an atom for the electrons in a covalent bond; If you had trouble with this question, review the following material: Atoms in a molecule attract shared bonding electrons to varying degrees, depending on the element. The more electronegative an atom is, the more strongly it pulls shared electrons toward itself.

Which of the following helps most to explain why water has a high specific heat?

(a) A water molecule can make 4 hydrogen bonds; Good job! When you heat water, much of the heat is used to break hydrogen bonds. Only the remaining heat can increase molecular motion, raising the temperature.

The open spaces in water's crystal structure make it possible for ...

(a) aquatic life to exist at the North Pole; Good thinking! The openings in the lattice make ice less dense than liquid water, so it floats. That causes water to freeze from the top down, so there's always liquid in which organisms can live.

Which statement is true of water's tensile strength?

(a), (b), and (c): (a) It results from hydrogen bonding, (b) It helps to pull water through plants, (c) It involves both cohesion and adhesion; Right! Because of hydrogen bonding, water coheres to itself and adheres to cell walls. That makes it possible to pull water through plants without breaking the water column.

The table shown here lists the specific heat of several substances. Substance | Specific heatJ/g/∘CJ/g/∘C water: 4.18 ethyl alcohol: 2.44 benzene: 1.80 sulfuric acid: 1.40 Based on the information in the table, which of the following statements are true?

- Water has a high specific heat due to the hydrogen bonding between water molecules. - Benzene is more resistant to temperature change than sulfuric acid. - More heat is required to raise the temperature of 1 g of water 1 ∘C∘C than to raise the temperature of 1 g of ethyl alcohol 1 ∘C∘C. - Sulfuric acid is less resistant to temperature change than water. Water has a high specific heat relative to other substances due to the hydrogen bonding that occurs between water molecules. Water is very resistant to temperature increases because the hydrogen bonds between the water molecules must be disrupted to raise the temperature of the water. By the same token, water must lose a large amount of heat and form many additional hydrogen bonds for its temperature to decrease. Water's high specific heat has some important consequences for life on Earth. For example, coastal areas generally have milder climates than inland areas due to the oceans' high specific heat. Oceans are able to absorb a large amount of heat during the daytime and summer, keeping air temperatures relatively cool. At night and during the winter, the oceans cool gradually, releasing heat and warming the air. Water's high specific heat also stabilizes ocean temperatures, resulting in a favorable environment for marine life.

Classify each statement as an example of adhesion, cohesion, or surface tension. Drag each statement to the appropriate bin.

Adhesion: Water molecules cling to the side of a beaker, Water molecules cling to plant cell walls. Cohesion: Water molecules are attracted to each other, A drop of water spilled on a table forms a drop on the table, rather than spreading out over the surface Surface Tension: A water strider runs across a pond without breaking the surface, A sewing needle floats when itis placed gently on top of the water in a bucket; Water exhibits several different properties due to its ability to form hydrogen bonds, including adhesion, cohesion, and surface tension. An example of adhesion is the hydrogen bonding between water and another type of molecule, such as the molecules composing the side of a water glass or beaker. Cohesion, on the other hand, is the attraction between like molecules. Water forms drops on a table because the water molecules are more strongly attracted to each other through hydrogen bonding than they are to the molecules composing the table's surface. Both adhesion and cohesion enable plants to transport water from the roots to the leaves against the force of gravity. Surface tension is the resistance of the surface of a liquid to stretching or breaking. Water's surface tension results from the hydrogen bonds formed between the water molecules at the surface and between those surface molecules and the ones below. Water's high surface tension is evident when certain insects are able to walk on the water's surface.

Which statement helps to explain why ice is less dense than liquid water?

Both (a) and (b): (a) Water molecules make hydrogen bonds at definite angles and (b) Cold molecules move less than warm molecules.

Water is a source of ______________ for chemical reactions in cells.

Both (a) and (b): (a) hydrogen atoms and (b) oxygen atoms; Good answer! Many reactions incorporate O and H from water into biological molecules. This happens when you digest starch and protein, for example.

Which factor is important in making it possible to cool yourself by sweating? Think carefully!

Both (a) and (b); (a) Molecules collide with varied angles and speeds and (b) Hydrogen bonds are relatively weak.; Good choice! Random collisions allow some molecules to accumulate more energy than other molecules. The weakness of hydrogen bonds lets those molecules escape, leaving the cooler molecules behind.

Explain the pattern of temperatures shown in the diagram.

During the summer, the coastal areas are cooler than the inland areas because the ocean moderates the climate near the coast by absorbing and releasing heat; Because of water's high specific heat, a large body of water can absorb and release large amounts of heat, moderating climates in coastal areas. During the summer, the coolest temperatures are found along the coast, with temperatures becoming warmer further inland.

Which of these bonds is weakest?

Hydrogen Bonds are weaker than covalent bonds because they do not involve sharing of electrons, and they are weaker than ionic bonds because they involve the attraction of partial (not full) opposite charges.

Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _____.

Hydrogen Bonds. The polarity of a water molecule allows the oxygen of one water molecule to bond weakly to the hydrogen of another water molecule.

Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?

Polar groups attract one another; Good thinking! Polar water molecules pull together, holding the polar parts of the amphipathic molecules and squeezing out the nonpolar parts. That leaves the nonpolar parts waving in the air.

Label the following diagram of water molecules, indicating the location of bonds and the partial charges on the atoms. Drag the labels to their appropriate locations on the diagram of the water molecules below. Labels can be used once, more than once, or not at all.

The image on the left shows the unequal sharing of electrons in a water molecule. Notice that the electrons are pulled toward the oxygen atom, which is more electronegative than a hydrogen atom, resulting in a partial negative charge (δ−δ−) on the oxygen atom and a partial positive charge (δ+δ+) on each hydrogen atom. The image on the right shows hydrogen bonding between two water molecules: the partially negative oxygen atom of one water molecule is attracted to the partially positive hydrogen atom of another water molecule. Hydrogen bonds are much weaker than covalent bonds. In liquid water, hydrogen bonds last only a fraction of a second, breaking and re-forming with great frequency. In a given instant, one water molecule can be hydrogen bonded to up to four other water molecules.

How does the pH of the solution on the right compare with that of the solution on the left?

The solution on the right is basic relative to the solution on the left; The solution on the right has a lower concentration of hydrogen ions relative to hydroxide ions than does the solution on the left.

Dissolving is best described as ...

a mingling of molecules and/or ions; Good! When sugar dissolves in water, the sugar molecules remain intact but mingle with water molecules. When salt (NaCl) dissolves, its Na+ and Cl- ions separately mingle with water.

Which property of water allows a paper towel to pick up a puddle of water?

adhesion of water molecules to other kinds of molecules; Water adheres to the cellulose molecules in a paper towel, allowing the towel to pick up a puddle of water. This is similar to the adhesion between water molecules and cellulose in cell walls responsible for water transport in plants.

Many of water's emergent properties, such as its cohesion, its high specific heat, and its high heat of vaporization, result from the fact that water molecules _____.

are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively; The formation of hydrogen bonds between the positive and negative regions of different water molecules accounts for most of water's unique properties.

The tendency of an atom to pull electrons toward itself is referred to as its _____.

electronegativity; The question defines electronegativity.

What process exerts the pull on water molecules that is relayed from leaf to root via cohesion?

evaporation; The evaporation of water from leaves moves water up from the roots via cohesion.

A water molecule can bond to up to _____ other water molecules by ____ bonds.

four ... hydrogen; As can be seen in the illustration on page 1 of the activity titled "The Polarity of Water" a water molecule is joined to four other water molecules by hydrogen bonds.

Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____.

high specific heat; Water has a high specific heat, meaning that a relatively large amount of heat must be added or removed in order to get the temperature of the water to change significantly.

Water has surface tension because ...

hydrogen bonds between surface water molecules resist being stretched; Good choice! The hydrogen bonds between surface water molecules are normally slightly stretched. Like a stretched sheet of rubber, the surface tends to contract and resists being penetrated.

What is the arrow pointing to?

hydrogen ion; The arrow is indicating a single proton, a hydrogen ion (H+)

In a neutral solution the concentration of _____.

hydrogen ions is equal to the concentration of hydroxide ions; This is the definition of a neutral solution.

What is the arrow pointing to?

hydroxide ion; The arrow is indicating a hydroxide ion (OH-)

Though you add heat, the temperature of boiling water remains constant because ...

it takes energy to break hydrogen bonds; Correct! At boiling, all the added heat is used to break hydrogen bonds. Free of the water mass, the departing steam carries away all the added energy, with none left over to raise the temperature.

The unequal sharing of electrons within a water molecule makes the water molecule _____.

polar; The electrons spend more time with the oxygen of the water molecule than with the hydrogens of water. Thus, the oxygen has a net negative charge and the hydrogens have a net positive charge.