Strong ions and charge-balance

Abstract

It has been shown that the ability to predict the pH in any chemically characterized fluid, together with its buffer-capacity and acid content can be based on the requirement of electroneutrality, conservation of mass, and rules of dissociation as provided by physical chemistry. More is not required, and less is not enough. The charge in most biological fluids is dominated by the constant charge on the completely dissociated strong ions but, nonetheless, a persistent narrative in physiology has problematized the notion that these have any role at all in acid-base homeostasis. While skepticism is always to be welcomed, some common arguments against the importance of strong ions are examined and refuted here. We find that the rejection of the importance of strong ions comes with the prize that even very simple systems such as fluids containing nothing else, or solutions of sodium bicarbonate in equilibrium with known tensions of CO₂ become incomprehensible. Importantly, there is nothing fundamentally wrong with the Henderson–Hasselbalch equation but the idea that it is sufficient to understand even simple systems is unfounded. What it lacks for a complete description is a statement of charge-balance including strong ions, total buffer concentrations, and water dissociation.

Keywords:

• Electrochemistry
• acid-base equilibrium
• chemistry
• physical
• ions
• buffers
• computer simulation
• models
• biological
• water-electrolyte balance

Disclosure statement

The author reports there are no competing interests to declare.

Data availability statement

R code to demonstrate the quantitative results and reproduce the figures are found here: https://figshare.com/s/209db01b9038f509ab93

Additional information

Funding

No funding was required for this work.