Electrolytes and pH
As you review this resource, notice the difference between a strong and weak acid and base. How do the pH measurements of acidic and basic solutions affect living organisms? Different foods have different amounts of hydrogen ions, which is also known as proton concentration.
pH
A solution's hydrogen ion concentration [H+] is an important property because biological systems contain functional groups whose properties are changed by changes in the hydrogen ion concentration.
Since the hydrogen ion concentrations are usually much less than one and can vary over many orders of magnitude, a different scale is used for the hydrogen ion concentration, the pH scale. The pH is the -log of the proton concentration:
pH = –log [H+].
The log conversion reduces a 10-fold change in hydrogen ion concentration to a one-unit change in pH. The minus sign changes the negative numbers obtained from log[H+] to positive ones. Since the pH scale is an inverse scale, the concentration of protons is high at low pH and low at high pH. A solution is considered acidic if the pH is less than seven and basic if the pH is above 7. A solution is neutral if its pH is equal to 7.0.
The image below shows the pH of several common fluids.
pH of Various Compounds
Biological compounds are on the left, and some foods and cleaning products are on the right.
Acid Dissociation and pH
For our studies, we will use the Bronsted definition of an acid. We will define an acid as a proton donor and a base as a proton acceptor. Hydrochloric acid, like sodium chloride, is a strong electrolyte because it completely dissociates in aqueous solution into charged ions. It is also a strong acid because when it completely dissociates, it also completely donates all of its protons.
Many molecules are weak electrolytes and exist in an equilibrium (indicated by ⇌ in the general equation below) between the starting molecule and its dissociated parts. Thus, dissociation can be seen as an acid (HA) in equilibrium with a proton (H+) and the corresponding conjugate base (A-).
In general:
HA ⇌ A- + H+
Specifically for Acetic acid:
CH3COOH ⇌ CH3COO- + H+
Source: Carnegie Mellon University, https://oli.cmu.edu/jcourse/workbook/activity/page?context=df459e6d0a0001dc64e18bdb857f2432
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