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Purdue University - Hydrogen Bonding and the Anomalous Properties of Water
Basic introduction to some of the unique qualities of water.

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Abnormal Psychology


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 aqueous colloidal suspension is the real world context for most biochemical processes with the solubility properties of macromolecules in water being a primary driver of 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 important in life processes.

Although you definitely may see some direct questions about water on the MCAT, beyond those, the aqueous solution context will be omnipresent on the exam. Simply put, aqueous solution is the most important field of play for phenomena both for general chemistry (solutions, acids & bases, and electrochemistry) and biology. Direct questions regarding the properties of water may involve its phase equilibria, for example. The H - O - H bond angle is another favorite, but beyond the direct questions, bear in mind that for many, many questions on the test, water will figure indirectly as the medium in which the phenomena in question are occuring. Just as the chemical behavior of water plays a crucial role in science, especially the science underlying medicine, understanding water is crucial for mastering the MCAT.


Heat and Temperature



Water has played a very important role in the history of measurement. The properties of water were used to develop the original definitions of many physical constants and units, and it's good practice to review the basis of many units in water. For many scientists, this becomes second nature.

The density of water at 4oC was originally taken as a physical standard to be the intersection of the units of length and units of mass in the S.I. system. What this means, in practical terms, is that you should know the density of water using a variety of units.

A cubic meter of water is 1000 liters. This contains 1000 kg of water. Cne cubic centimeter of water contains one gram.

The fact that the measurement of volume and mass agree in the density of water is for the convenience of chemists.

As an additional important example of the role of water in the history of measurement, the unit of heat flow which is second in importance only to the joule, the calorie, was defined as the amount of heat to raise the temperature of 1 gram of water 1 degree Celsius, the Celsius unit itself being defined so that 100 units of Celsius temperature should separate the freezing and boiling points of water at 1 atm.

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