Integrated SequencePhysics Chemistry Organic Biology

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Module 8 in the Syllabus

Water Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Water
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Overview of Water
The only common substance found naturally in all three states of matter, the liquid form of water is the most abundant substance on the Earth's surface. The solid phase of water, ice, is actually less dense than the liquid phase. What are some of the other physical and chemical properties of water that make it so vital for life? The solvent properties of water are essential for life processes as we understand them. Aqueous solution or suspension is the real context of biochemistry with the solubility properties of macromolecules in water being a primary driver of their biochemical behavior. The ability of water to form strong hydrogen bonds is at the heart of its solvency. The surface tension, dielectric properties, and amphoteric nature of water are all unique and necessary for life.

Water on the MCAT
Although you will only see a few direct questions about water on the MCAT, the aqueous solution context is simply the most important field of phenomena for both general chemistry (solutions, acids & bases, and electrochemistry) and biology. Direct questions regarding the properties of water entail things like its phase equilibria. The H - O - H bond angle is a favorite, but for many, many questions on the test, water will figure directly as the medium of the system. Just as the chemical behavior of water plays a crucial role in science, especially a view of general science leading to medicine, water is crucial for the test.

Conceptual Vocabulary
WaterWater is a common chemical substance that is essential to all known forms of life, typically referred to in its liquid form or state, but also having a solid state, ice, and a gaseous state, which are commonly encountered.
Water vaporWater vapor is the gas phase of water.
IceIce is the name given to any one of the 14 known solid phases of water.
HydroniumHydronium is the common name for the cation derived from protonation of water.
HydroxideHydroxide is the most common name for the diatomic anion, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base.
FogFog is a cloud in contact with the ground.
DehydrationDehydration (hypohydration) is the removal of water from a substance.
Hydrogen bondA hydrogen bond is a special type of dipole-dipole bond that exists between an electronegative atom and a hydrogen atom bonded to another electronegative atom.
HydrophilicityHydrophilicity refers to a physical property of a molecule that can transiently bond with water through hydrogen bonding.
HydrophobicityHydrophobicity refers to the physical property of a moleculethat is repelled from a mass of water
OsmosisOsmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient.
AquiferAn aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well.
GroundwaterGroundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations.
PrecipitationPrecipitation is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface.
Dew pointDew is water in the form of droplets that appears on thin, exposed objects in the morning or evening.
SteamIn physical chemistry, and in engineering, steam refers to vaporized water.
Self-ionization of waterThe self-ionization of water is the chemical reaction in which two water molecules react to produce a hydronium and a hydroxide ion.
AmphiphileAn amphiphile is a chemical compound possessing both hydrophilic and hydrophobic properties.
Water cycleThe Earth's water is always in movement, and the hydrologic or water cycle describes the continuous movement of water on, above, and below the surface of the Earth.
Heavy waterHeavy water is water which contains a higher proportion than normal of the isotope deuterium, as deuterium oxide, or as deuterium protium oxide.
HydrologyHydrology is the study of the movement, distribution, and quality of water throughout the Earth.
Hard waterHard water is water that has a high mineral content, in contrast with soft water.
Reverse osmosisReverse osmosis the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.
Tritiated waterTritiated water is a form of water where the usual hydrogen atoms are replaced with tritium.
Water dimerThe water dimer consists of two water molecules loosely bound by a hydrogen bond. It is the smallest water cluster.
Advanced terms that may appear in context in MCAT passages
Amorphous iceAmorphous ice is an amorphous solid form of water, meaning it consists of water molecules that are randomly arranged like the atoms of common glass.
Clathrate hydrateClathrate hydrates are a class of solids in which gas molecules occupy cages made up of hydrogen-bonded water molecules.
Super hydrophilicitySuper hydrophilicity describes the effect where under light irradiation, water dropped onto titanium dioxide forms no contact angle (almost 0 degrees).
Mpemba effectThe Mpemba effect is the observation that, in some specific, fairly common circumstances, hotter water freezes faster than colder water.

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