Summarizing Water

Summary of Lessons So Far

Water has many properties that are critical to maintaining life. Generally, it is a polar molecule, allowing for the formation of hydrogen bonds. Hydrogen bonds allow ions and other polar molecules to dissolve in water. Therefore, water is an excellent solvent.

The hydrogen bonds between water molecules cause the water to have a high heat capacity. This means it takes a lot of added heat to raise its temperature. As the temperature rises, the hydrogen bonds between water continually break and form anew. Thus, this allows for the overall temperature to remain stable, although the system gets additional energy.

Water also exhibits a high heat of vaporization. As a matter of fact, this is key to how organisms cool themselves by the evaporation of sweat. Water’s cohesive forces allow for the property of surface tension, whereas its adhesive properties are seen as water rises inside capillary tubes.

The pH value is a measure of hydrogen ion concentration in a solution. It is one of many chemical characteristics that is highly regulated in living organisms through homeostasis. Acids and bases can change pH values, but buffers tend to moderate the changes they cause. These properties of water are intimately connected to the biochemical and physical processes performed by living organisms, and life would be very different if these properties were altered, if it could exist at all.

Glossary of Words

Acid

molecule that donates hydrogen ions and increases the concentration of hydrogen ions in a solution

Adhesion

attraction between water molecules and other molecules

Base

molecule that donates hydroxide ions or otherwise binds excess hydrogen ions and decreases the concentration of hydrogen ions in a solution

Buffer

substance that prevents a change in pH by absorbing or releasing hydrogen or hydroxide ions

Calorie

amount of heat required to change the temperature of one gram of water by one degree Celsius

Capillary action

occurs because water molecules are attracted to charges on the inner surfaces of narrow tubular structures such as glass tubes, drawing the water molecules to the sides of the tubes

Cohesion

intermolecular forces between water molecules caused by the polar nature of water; responsible for surface tension

Dissociation

release of an ion from a molecule such that the original molecule now consists of an ion and the charged remains of the original, such as when water dissociates into H+ and OH

Evaporation

separation of individual molecules from the surface of a body of water, leaves of a plant, or the skin of an organism

Heat of vaporization of water

high amount of energy required for liquid water to turn into water vapor

Hydrophilic

describes ions or polar molecules that interact well with other polar molecules such as water

Hydrophobic

describes uncharged non-polar molecules that do not interact well with polar molecules such as water

Litmus paper

(also, pH paper) filter paper that has been treated with a natural water-soluble dye that changes its color as the pH of the environment changes so it can be used as a pH indicator

pH paper

see litmus paper

pH scale

scale ranging from zero to 14 that is inversely proportional to the concentration of hydrogen ions in a solution

Solvent

substance capable of dissolving another substance

Specific heat capacity

the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius

Sphere of hydration

when a polar water molecule surrounds charged or polar molecules thus keeping them dissolved and in solution

Surface tension

tension at the surface of a body of liquid that prevents the molecules from separating; created by the attractive cohesive forces between the molecules of the liquid

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