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.