Ph lab

Páginas: 12 (2788 palabras) Publicado: 1 de abril de 2011
The Marvelous Water Molecule
Water is an important part of all life. The earth’s surface is about 70% water and all living organisms on earth have water in them. Humans are made up of about 66% water and chickens are about 75% water. Lettuce is about 90% water. While the amount of water needed changes from one organism to another, water is one of the basic requirements for life onearth.
A water molecule is made up of three atoms: two hydrogen atoms and one oxygen atom. This is why the formula or short-hand for water is written as H2O (two hydrogens or H2 and one oxygen or O). Hydrogen atoms are smaller than the oxygen and have a positive charge while the oxygen atom is bigger and has a negative charge. Because of the shape of the molecule, water has a positive endand a negative end causing the molecule to act like a magnet! +
Oxygen _
These magnet-like positive and negative charges give water special abilities. Molecules of water can actually stick or bond to each other to form chains just like magnets can stick to each other. These chains of water molecules createa type of surface film which allows this water strider to float on water.
Photo by:
George I. Bernard/Animals Animals
Another quality of water is called dissociation. This property of water is responsible for the formation of acids and bases. In water dissociation, a hydrogen atom breaks away from the oxygen atom. Here is an example of what happens+

The chemical reaction is written like this:
H2O ↔ H+ + OH-
Water equals one hydrogen ion plus one hydroxide ion

In pure water there are an equal number of H+ ions and OH- ions. The amount or number of H+ ions to OH- ions determines the pH of a substance or whether the substance is acid, base or neutral. This brings us to the pHscale. [pic]

The pH scale is a measure of the strengths of acids and bases.
Søren Sørensen visting Cornell University in 1924: Courtesy Edgar Fahs Smith Memorial Collection, Department of Special Collections, University of Pennsylvania Library.
The pH scale was developed by Dr. Sorenson (above) in the early 1900’s. It is believed that he developed the pH scale to aid the brewingindustry. He published his information about pH in 1920. The letters pH stand for "pondus hydrogenii" or the potential for hydrogen (H+). The pH scale ranges from 0 to 14, where 0 is the pH of very strong acids and 14 is the pH of very strong bases. Pure water has a pH of 7 and is a neutral solution, which means it is neither acidic nor basic and has an equal number of H+ ions and OH- ions.
Acids• Acids are substances that have hydrogen ions (H+).
• The more H+ the stronger the acid.
• Acids taste sour.
• Vinegar, Citrus Fruits & Coca-Cola are examples of acids.
• Any substance with a pH less than 7 is considered an acid.

• Bases are substances that have hydroxide ions (OH-)
• The more OH- the stronger the base.
• Bases taste bitter and feelslippery, almost soapy (soaps are actually basic!).
• Bleach, Ammonia & most cleaning products are examples of bases.
• Any substance with a pH greater than 7 is considered a base.

The lower the pH of a solution the more acidic it is and the higher the pH of a solution the more basic it is. A solution of lemon juice or Coca-cola that has a pH of 2 is more acidic than Seven-up which hasa pH of 4. However, lemon juice is not twice as acidic as Coca-Cola! The lemon juice with a pH of 2 is actually one hundred times more acidic than the Seven-up with a pH of 4 and has one hundred times more H+ ions! The pH scale is based on an increase or decrease by a power of ten. Root beer is ten times more acidic than pure water! Pure water has a pH of 7 and root beer has a pH of 6,...
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