Upload
shavonne-beasley
View
219
Download
0
Tags:
Embed Size (px)
Citation preview
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.
SolutionBuffers: 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.