# PH and Buffers. Water Characteristics  The covalent bonds within the water molecule, like the hydrogen bonds between the molecules, can also break spontaneously.

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pH and Buffers

Water Characteristics  The covalent bonds within the water molecule, like the hydrogen bonds between the molecules, can also break spontaneously. This is known as water dissociation. H2O  H+ + OH- Water Hydrogen Ion Hydroxide Ion  This doesn’t happen often, but enough. If you have a beaker of pure water, 1/10,000,000 molecules are hydrogen ions.

pH  If you want to mathematically express the concentration of the hydrogen ions found in a solution, you would refer to the solution’s “pH”.

Key Features of pH Scale  Acid, Base, Neutral Range  Acids are molecules that donate hydrogen ions to a solution.  In a chemical formula, acids start with “H”. Ex. HCl, HF (hydrochloric acid, hydrofluoric acid)  Bases are molecules that combine with hydrogen ions to remove them from a solution  In a chemical formula, end with “OH”. Ex. NaOH, KOH (sodium hydroxide, potassium hydroxide)  Scale is Logarithmic

Calculating pH: A couple key formulas:  [H + ] + [OH - ] = 1 x 10 -14  pH + pOH = 14  If given the concentration, pH or pOH is simply the exponent on the 10.  Ex. [H + ] = 1 x 10 -2 the pH would be 2.  If given the pH, the [H + ] would be calculated by making the pH value the negative exponent of the 10.  Ex pH = 9, [H + ] = 1 x 10 -9.

Why is pH important to living organisms?  Key molecules, known as enzymes, function at set pH values.  All our cells function within a certain pH range.  If the fluids bathing those cells is “off” these cells won’t function at max capacity.  Other than just cells, our blood needs to be at a certain pH.

But…  The chemical reactions of life constantly produce acids and bases within cells. These have a tendency to throw off the pH values. We need some sort of mechanism to minimize how much the pH is altered.

Solution  Buffers: substance that can take up or release hydrogen ions into a solution so that the pH can maintain equilibrium.  So...if pH is low, what about the [H + ]?  It is HIGH ...if pH is high, what about the [H + ]?  It is LOW

Buffers  What would a buffer do if pH falls?  Remove hydrogen ions from the solution.  What would a buffer do if pH rises?  Donate hydrogen ions to the solution.  In living organisms a key buffer is known as the Bicarbonate Ion Buffer System.

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