AP Biology : Understanding Essential Properties of Water

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Ap Biology

The property of water that contributes to its ability to stick to certain surfaces is called __________.

Possible Answers:

Adhesion

Polymerization

Parsimony

Cohesion

Gravity

Correct answer:

Adhesion

Explanation:

Water is a polar molecule, and thus can adhere to different surfaces; thus, adhesion is the correct answer here. Cohesion is close, as cohesion describes the ability of water to stick to itself due to its polarity. We want the property that allows water to stick to other surfaces, not to itself. Polymerization involves chains of similar molecules, and does not occur in water. Parsimony is the principle that the simplest explanation is usually the reality of a situation (such as when tracing evolutionary histories). Gravity does not play into the properties of water.

Example Question #1 : Understanding Essential Properties Of Water

Water's ability to create intermolecular hydrogen bonds results in its inability to break up which of the following compounds?

Possible Answers:

Ions

Sugars

Lipids

Amino acids

Correct answer:

Lipids

Explanation:

Nonpolar compounds will not be adequately dissolved in aqueous solutions. Lipids are nonpolar compounds that are mainly insoluble in water. This causes lipids to congregate together, rather than be broken apart in aqueous solutions. Lipids will generally come together to form globs or balls called micelles.

Ions, amino acids, and sugars (carbohydrates) are all polar, and will be adequately dissolved and ionized by water.

Example Question #3 : Understanding Essential Properties Of Water

What property of water allows it to have a very high boiling point?

Possible Answers:

Van der Waals forces

Autoionization

Amphoteric nature

Salt formation

Hydrogen bonding

Correct answer:

Hydrogen bonding

Explanation:

Water has an unusually high boiling point for a liquid. This is related to the intermolecular forces between water molecules; when a liquid has particularly large intermolecular forces, it will have a higher boiling point. Large intermolecular forces between molecules will favor the liquid state over the gaseous state.

Water is made up of oxygen and hydrogen and can form hydrogen bonds, which are particularly strong intermolecular forces. These strong intermolecular forces cause the water molecules to "stick" to one another and resist transition to the gaseous phase.

Example Question #2 : Understanding Essential Properties Of Water

Which of the following intermolecular interactions is easiest to disrupt via a change in temperature?

Possible Answers:

Hydrogen bonds 

Peptide bonds 

Ionic bonds 

Covalent bonds 

Correct answer:

Hydrogen bonds 

Explanation:

Hydrogen bonding can easily be disrupted by changes in temperature. It is important to note that hydrogen bonding is not a true example of a chemical bond, but rather an intermolecular force. Hydrogen bonds are essential for the formation of protein structure and DNA base pairing. When proteins and DNA are exposed to heat, they degrade as these hydrogen bonds are broken.

Covalent bonds, which include peptide bonds, and ionic bonds are examples of real chemical bonds that require high amounts of energy before they can be easily disrupted. These bonds are considered more permanent interactions than other intermolecular forces.

Example Question #2 : Ap Biology

In reference to water, what to do cohesion, surface tension, and adhesion all have in common?

Possible Answers:

All are properties related to hydrogen bonding

All are aspects of a crystalline structure

All are results of the structure of hydrogen atoms

All are produced by covalent bonding

All are produced by ionic bonding

Correct answer:

All are properties related to hydrogen bonding

Explanation:

These properties of water are all a result of hydrogen bonding. Hydrogen bonds result from the electrical attraction between partially positive hydrogen atoms and partially negative oxygen atoms of adjacent water molecules. The differences in electronegativity between hydrogen and oxygen give rise to the hydrogen bonding and associated properties.

Attraction and polarity in water molecules cause them to "stick" to one another. Attraction between water molecules results in cohesion, and attraction between the water molecules and other compounds in the environment results in adhesion. The high surface tension of water is caused by the "sticking" of water molecules to one another, which keep vapor pressure low.

Hydrogen bonding is a temporary intermolecular force, and is different from covalent or ionic bonding. Covalent and ionic bonding result in permanently joined atoms to build molecular structures.

Example Question #6 : Understanding Essential Properties Of Water

It is a hot summer day. When you clutch a cold glass of water, how is heat energy transferred?

Possible Answers:

From your hand to the glass by radiation

From the glass to your hand by conduction

From the air to your hand by convection

From your hand to the glass by conduction

From the glass to your hand by radiation

Correct answer:

From your hand to the glass by conduction

Explanation:

There are three forms of heat transfer: radiation, convection, and conduction. Radiation is the transfer of heat via electromagnetic waves, such as sunlight of microwaves. Convection is the transfer of heat through a fluid medium, such as water or air currents. Conduction is the direct transfer of heat between environments through physical contact. Since your hand is in physical contact with the glass, heat is transferred by conduction.

Heat is always transferred from a body of higher temperature to a body of lower temperature. Since your hand is warmer than the glass, heat is transferred from the hand to the glass. It can be easier to think of heat transfer in terms of concentration. Like molecules, heat energy will travel from a region of high concentration (hotter) to a region of low concentration (colder) in order to reach equilibrium.

Example Question #3 : Understanding Essential Properties Of Water

Water often travels between cells and the environment via osmosis, where it diffuses from areas with low solute concentration (where more water is present) to areas with higher solute concentration (where there is relatively less water). Which answer choice is an example of osmosis?

Possible Answers:

A normal cell is placed in pure water; water from the environment flows into the cell and causes it to swell

A normal cell is placed in pure water; water from the cell flows out into the surrounding liquid and causes the cell to shrink

A cell is placed in an isotonic environment and immediately loses a great deal of its water content to its surroundings

A cell is placed in a hypertonic environment; water flows into the cell and causes it to swell

Correct answer:

A normal cell is placed in pure water; water from the environment flows into the cell and causes it to swell

Explanation:

To select the correct answer, you must understand the difference between hypertonic, hypotonic, and isotonic. A hypertonic solution, such as ocean water with a high salt content, contains more solute than a normal cell. Water will flow out of the cell and into the environment in an attempt to equalize the amount of solute in the two "compartments." An isotonic solution has the same relative amount of solute as the cell to which it is being compared, so no concentration gradient exists and no net diffusion will occur. Finally, a hypotonic solution contains less solute than the cell too which it is being compared.

Pure water will always have less solute concentration than a cell, creating a hypotonic relationship. The solution is hypotonic to the cell (less solute) and the cell is hypertonic to the water (more solute). Water will flow from the hypotonic environment to the hypertonic cell, causing it to swell in size.

Example Question #3 : Understanding Essential Properties Of Water

What causes water's high heat capacity?

Possible Answers:

Adhesion

Low boiling point

Low density as a solid

Cohesion

Correct answer:

Cohesion

Explanation:

Cohesion is the result of increased strength of hydrogen bonding between many water molecules. This increased strength requires a great amount of heat in order to break the hydrogen bonds between molecules, in order for these molecules to become vapor. Cohesion and hydrogen bonding are the cause for water's low vapor pressure, high boiling point, and high heat capacity.

Adhesion is water's property to adhere to a surface, and is the cause of capillary action. Water does have low density as a solid, which allows ice to float, but is not the reason for water's high heat capacity. Water has a high boiling point, considering its low mass.

Example Question #4 : Ap Biology

Which phase of water in the most dense?

Possible Answers:

Liquid

Water has the same density in any of its phases

Supercritical fluid

Solid

Gas

Correct answer:

Liquid

Explanation:

Water, unlike many other compounds, has several special properties due to its hydrogen bonding between molecules. The hydrogen bonds are relatively strong, leading water to have very low vapor pressure and high surface tension. A side effect of the hydrogen bonding, however, is that when water crystallizes, the molecules will inevitably align so that the hydrogen bonds are maintained. The solid lattice structure of water molecules is, thus, not very tightly packed. The structure is ideal to optimize intermolecular forces, rather than space and volume. The density of the solid (ice) is thus less than the density of the liquid water.

Water vapor (gas) and supercritical water both have lower densities than ice, making liquid water the most dense.

Example Question #5 : Understanding Essential Properties Of Water

What property of water allows it to have an unusually high boiling point?

Possible Answers:

It contains oxygen

It is a small molecule that can pack tightly

It has a low molecular weight

It is in a bent shape

It can form hydrogen bonds

Correct answer:

It can form hydrogen bonds

Explanation:

Boiling point is generally determined by a few factors that are directly related to molecular weight and intermolecular forces. In general, lighter molecules have lower boiling points and molecules with stronger intermolecular forces have higher boiling points.

Water is relatively light, but has very strong hydrogen bonding. Hydrogen bonding is the strongest intermolecular force and will act to pull water molecules closer to each other. The result is a dense liquid that does not easily transition into a less dense gas. In order for water to boil these intermolecular hydrogen bonds must be broken, which takes energy. A greater energy input means a higher boiling point.

The shape and composition of water are not particularly relevant to its boiling point, and being a small, light molecule would be conducive to a low boiling point rather than a high boiling point.

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