Understanding Essential Properties of Water - AP Biology

Hydrogen bonds are the intermolecular forces that allow it to engage in cohesion. Ionic bonds are strong bonds within a molecule between a cation and anion. Polar covalent bonds are bonds within a molecule in which there is a slight charge on the elements. Nonpolar covalent bonds are bonds within a molecule in which there is no charge on the elements.

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.

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.

The properties of water make it essential to life. Cohesion refers to its ability to form hydrogen bonds, attracting the molecules together and contributing to its high surface tension. Adhesion refers to water's attractive properties to other substances, and helps processes like absorption through the xylem. Solid ice is less dense than liquid water, allowing life to exist below the frozen surfaces of lakes and ponds. The polarity of water is essential for numerous biological processes and makes it a good solvent for most biological molecules. Finally, the high specific heat of water makes it resistant to temperature change, allowing life forms to maintain relatively constant internal temperatures.

The high specific heat and surface tension of water contribute to its high boiling point, helping to keep it in liquid form for most biological processes.

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.

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.

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.

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.

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.

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.

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.

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.

Adhesion refers to the attraction between water molecules and foreign particles or surfaces. Cohesion refers to the attraction between one water molecule and another.

Adhesion of water to the cell walls of the xylem vessels and cohesion of water molecules to one another allow for water transport in plants. This is also known as capillary action.

The high heat capacity, low solid density, and polarity of water, as well as its use as a solvent, are all essential to the role of water in supporting life in other ways.

The high specific heat of water means that it requires a large amount of heat to raise the temperature of water. This helps the temperature of the environment from becoming too hot or too cold. Also, humans are about 66% water, thus this property of water helps us regulate our body temperature too. Evaporative cooling helps prevent bodies from overheating. We have evolved to take advantage of this property of water, perspiring through our skin to cool it down during exercise. The fact that ice floats protects lakes from further cooling by cold wind. The fact that water is such a good solvent for polar molecules allows the chemistry of life to occur. Recall that life uses four main biomolecules, and dehydration synthesis and hydrolysis reactions occur constantly.

In osmosis, water diffuses through selectively permeable membranes to regions where the concentration of solute is higher (hypertonic). Osmosis is not the movement of the solute particles.

A hypertonic solution has a higher concentration of solute than the solute in the cell. Water diffuses to the higher concentration of solute, so water diffuses out of the cell, and the cell shrivels up. One way to think of this is that water follows "salt," as salt is the most common biological solute.

When the solution is hypotonic to the cell, the concentration of solute outside the cell is less. The water diffuses to the higher concentration inside the cell and causes the cell to swell with water, at it may burst.

The bond between oxygen and hydrogen in water molecules involves the sharing of electrons in which the oxygen atom pulls the electrons towards it more than the hydrogen pulls the electron. This results in a slight negative charge on the oxygen and a slight positive charge on the hydrogen. The bond is not ionic because electrons are not totally transferred, rather they are shared.

Acidic compounds and solutions release hydrogen () ions. Basic compounds and solutions release ions and take up hydrogen ions. Because of their charge acidic compounds and solutions do not mix well with oil, which is nonpolar.