WATER ALSO KNOWN AS… THE DEADLY DIHYDROGEN MONOXIDE

WHY SO SERIOUS? Water is vital to life…it’s that simple. All living things contain, use and rely upon water. It’s the properties of water that make it so versatile and an absolute requirement for life. It is found in all cells and tissues – major component of cytoplasm. Aids in thermoregulation. Aids in excretion. Keeps eyeballs moist, lubricates joints and is a shock absorber. Required for various anabolic and catabolic reactions – dehydration synthesis and hydrolysis.

PROPERTIES OF WATER It forms hydrogen bonds with other water molecules – both in liquid and solid form. (The water lattice.) Water is cohesive due to these same hydrogen bonds. Water is adhesive due to the hydrogen bonds as well. Its less dense as a solid than a liquid…which is odd. It has a high specific heat capacity. (The amount of heat required to raise the temperature by 1°C.)

PROPERTIES OF WATER

I LOVE YOU…I HATE YOU From chemistry…remember the phrase, “Like Dissolves Like”. Polar substances will dissolve in other polar substances…and nonpolar substances will not. Water dissolves polar substances because it is polar and small. It surrounds the particles of the other polar substance in what is called a “hydration shell”. The hydration shell prevents the substance being dissolved from reestablishing bonds and reforming. Substances that are polar or charged, are attracted to water, and dissolve readily in water and are called hydrophilic – water loving – molecules. Substances that are non polar will not dissolve in water and are called hydrophobic – water fearing – molecules.

DISSOLVING in WATER Hydration Shell

IONIZATION & pH Water has the ability to dissociate (separate) into ions. Water can even ionize itself – autoionization – which produces equal numbers of hydronium and hydroxide ions. Acids and bases react in water (forming aqueous solutions) that produce predictable outcomes (ions). Acids will produce hydronium ions (H 3 O + ) in water. Bases will produce hydroxide ions (OH - ) in water. The strength of an acid or base depends on the degree to which they ionize in water. Strong acids and bases will fully dissociate when they are placed in water. Weak acids and bases will only partially dissociate in water.

The pH SCALE The pH scale (portenz of hydrogen) measures the strength of an acid or base. It ranges from is the range of acids is the range of bases. 7 is perfectly neutral. Each step on the pH scale represents an increase or decrease of 10x (depending on which way you’re going).

NEUTRALIZATION Rx & BUFFERS Neutralization reactions occur between acids and bases. When the two mix, they form water and a salt. Acid + Base  Water + Salt Living things often require that areas within their bodies maintain an internal pH that they must control in order to maintain homeostasis, and therefore; proper function. To do this, living things will employ buffer systems. Buffers are chemicals that can compensate for pH changes because they can accept or donate protons (H + ). An example of this is the carbonic acid/bicarbonate blood buffer system. (Blood has to be kept at ) H 2 CO 3  HCO H +

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