Emergent properties of water
Hydrogen bonds drive these:
1. Cohesive behavior (helps transportation due to cohesion, adhesion and surface tension)
2. Ability to moderate temperature (water has high specific heat and high heat of vaporization, in addition to evaporative cooling, this
Cohesion
Binding together of like molecules, often by hydrogen bonds.
In water, the fragile hydrogen bonds that form, break and reform constantly hold water molecules together.
Cohesion due to hydrogen bonding contributes to the transport of water and dissolved nu
Adhesion
Attraction between different kinds of molecules.
Water molecules are attracted to charged surfaces and will spread out along the surface, this is why surfaces get wet.
Adhesion of water to cell walls by hydrogen bonds helps counter the downward pull of gr
Surface tension
Measure of how difficult it is to stretch or break the surface of a liquid.
Water has a greater surface tension than most other liquids because of the hydrogen bonding of surface molecules, which explains how some animals can walk on water.
Kinetic energy
Energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other motion.
Atoms and molecules have kinetic energy because they are always moving. The faster they move, the greater their kinetic energy.
Heat
Measure of the matter's total kinetic energy due to motion of its molecules. Depends in part on the matter's volume. Also called thermal energy. Heat is energy in its most random form.
Temperature
Measure of heat intensity that represents the average kinetic energy of the molecules, regardless of volume.
When two objects of different temperature are brought together, heat passes from the warmer to the cooler object until the two are the same temper
Calorie (cal)
Amount of heat energy required to raise the temperature of 1 gram of water by 1 degree centigrade at atmospheric pressure, or the amount of heat that 1 g of water releases when it cools by 1 degree centigrade.
Kilocalorie (kcal)
A thousand calories; amount of heat energy required to raise the temperature of one kilogram of water by one degree at one atmosphere pressure
Joule (J)
Unit of energy equivalent to 0.239 calories. One calorie equals 4.184J.
Specific heat
Heat that must be absorbed or lost for 1g of a substance to change its temperature by 1 degree centigrade.
Water has an unusually high specific heat, it resists changing temperature when it absorbs or releases heat as much of the heat is used to disrupt h
Vaporization
Transformation from a liquid to a gas resulting from the movement of molecules that overcome their attraction to other molecules. Also called evaporation.
Heat of vaporization
Quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.
Water has a high heat of vaporization because the hydrogen bonds must be broken before molecules can be transformed into gas. This accounts for the s
Evaporative cooling
Process in which the surface of an object becomes cooler during evaporation, owing to a change of the molecules with the greatest kinetic energy from the liquid to the gaseous state. As a liquid evaporates, the remaining surface of the liquid cools down.
Colloid
Mixture of a liquid and particles that (because of their large size) remain suspended rather than dissolved in the liquid.
Example: various molecules in the cell.
Hydrophobic
Lacking affinity for water, tending to coalesce and form droplets in water. Common in nonionic, nonpolar and other substances that can't form hydrogen bonds, often because of the prevalence of relatively nonpolar covanelt bonds.
pH
Measure of hydrogen ion concentration equal to -log[H+] and ranging in value from 0 to 14.
Each pH unit represents a tenfold difference in H+ and OH- concentrations.
pH declines as H+ concentration increases (and OH- decreases).
The pH of a neutral aqueou
Base
Substance that increases the concentration of OH- and reduces the hydrogen ion concentration of a solution by forming water.
Some bases reduce the H+ concentration by accepting hydrogen ions (i.e. ammonia, NH3), others reduce the H+ concentration by disso
Buffer
Substance made from a weak acid and its conjugate base in a solution that minimizes changes concentration of H+ and OH- in a solution (changes in pH).
Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions to the s
Acid
Substance that increases the hydrogen ion concentration of a solution and removes hydroxide ions because of the tendency for H+ to combine with OH- forming water.
Example: hydrochloric acid (HCl), when added to water, hydrogen ions dissociate from chlorid
Molarity
Concentration measured by the number of moles of solute per liter of solvent. Often used for aqueous solutions.
Solution
Liquid homogeneous mixture of two or more substances.
Hydrogen ion
Positively charged atom of hydrogen. Single proton with a charge of 1+. Results from the dissociation of water, along with the hydroxide ion.
Hydroxide ion
Anion OH having one oxygen and one hydrogen atom. Water molecule that lost a proton and now has a charge of 1-.
Hydration shell
Sphere of water molecules around each dissolved ion. The oxygen regions of the water molecules are negatively charged and attracted to cations, the hydrogen regions are positively charged and attracted to anions.
Hydrophilic
Having a strong affinity for water. Some substances can be hydrophilic without actually dissolving, they remain suspended as a colloid.
Example: cotton, explaining why a cotton towel dries and doesn't dissolve when washed.
Solvent
The dissolving agent of a solution.
Water is the most versatile solvent known.
Acid precipitation
Rain, snow, or fog that is more acidic than pH 5.2. Results from the reaction of sulfur and nitrogen oxides (from burning fossil fuels) with water in the air. Can damage life in lakes and streams and adversely affect plants by changing soil chemistry.
Solute
Substance that is dissolved in a solution.
Hydronium ion
Hydrogen ion combines with a water molecule to form a hydronium ion, H3O(+). Water that has an extra proton bound to it. Represented by convention as an hydrogen ion H+ which is always associated with another water molecule in the form of H3O(+).
Mole (mol)
Number of grams of a substance that equals its molecular weight in daltons and contains Avogadro's number of molecules.
There are 6.02x10^23 daltons in 1 g.
Molecular mass
Sum of the masses of all the atoms in a molecule; sometimes called molecular weight.
Aqueous solution
Solution in which water is the solvent.
In any aqueous solution at 25 degrees centigrade, the product of the H+ and OH- concentrations is constant at 10^-14:
[H+][OH-] = 10^-14
Molar mass
Mass in grams of 1 mol of a substance.
Water in solid state
When temperature falls to 0 degrees centigrades, water begins to freeze because more and more of its molecules are moving too slowly to break hydrogen bonds. The molecules lock into a crystalline lattice, wach water molecule hydrogen bonded to four partne
Water dissociation
Reversible reaction that occurs when an hydrogen atom participating in a bond between two water molecules shifts from one molecule to the other, leaving its electron behind (H+) and a water molecule that has lost a proton (OH-).
Equilibrium occurs when wa
Ocean acidification
Decreasing pH of ocean waters due to absorption of excess atmospheric CO2 from the burning of fossil fuels. Reduces the carbonate concentration, affecting marine life because carbonate is require for calcification by many marine organisms.