Very confused about Naunyn definition of acid and base

[red65]

TL;DR Summary

i can't grasp naunyn defintion of acid and base

First so that you can have some background I'd like to share an excerpt from the online lecture I'm studying. Here's a sample:

"1880-Arrhenius defines an acid as a substance that , when dissolved in water, produces an increased concentration of hydrogen ions.

1900-Naunyn combines Arrhenius' definition with Farady"s previous supposition that anions such Cl- are "base forming" (i.e. an acid) and cations such ass Na+ are "acid forming" (i.e. a base) thus acid-base status wasn't determined solely by [H+] but also by a number of other common electrolytes"

can someone explain to me how sodium behaves like a base and how chloride behaves like an acid (maybe equation that show sodium sequester a proton and another showing chloride somewhat provoking the release of a proton )

 

[Borek]

I can be wrong, but it seems to me you are trying to understand the definition in terms of our todays understanding of what the acid is. If so, it probably won't work - I strongly doubt Naunyn thought in terms of H⁺, more likely he thought something like "when there is chlorine present solution becomes acidic" and "when there are alkali/alkaline metal earth present solution becomes/is basic" (hard to tell what was the exact wording without trying to find/read the original paper).

Obviously he was wrong, which is why we are still taught Arrhenious definition, and Naunyn these days gets points only in historical books, only for the effort.

 

[Rougesang]

When sodium ion (Na⁺) is dissolved in water, it does not directly act as a base by accepting a proton (H⁺) from water. Instead, sodium ion remains as Na⁺ and does not participate in proton transfer reactions. Its behavior is more characteristic of a spectator ion in solution, meaning it doesn't actively participate in the chemistry of the solution.

On the other hand, chloride ion (Cl⁻) can indirectly influence the acidity of a solution. When chloride ion is dissolved in water, it does not directly donate a proton like an acid. However, its presence can affect the pH indirectly. Chloride ions are conjugate bases of strong acids (such as HCl), meaning they can accept protons under certain conditions. In the presence of a strong acid, chloride ions can react with protons to form the weak acid, HCl. This reaction can shift the equilibrium of other acid-base reactions in the solution, effectively influencing the pH.

An equation to illustrate this concept would involve the dissociation of hydrochloric acid (HCl) into its ions:

HCl(aq)⇌H+(aq)+Cl−(aq)

In this reaction, chloride ions (Cl⁻) are formed when hydrochloric acid (HCl) dissociates in water. While chloride ions themselves do not directly donate protons, they can combine with protons released from strong acids like HCl, effectively affecting the acidity of the solution.

It's important to note that in the context of acid-base chemistry, the terms "acid" and "base" are defined based on their behavior in aqueous solutions, rather than their intrinsic properties. So while sodium ion doesn't behave as a base and chloride ion doesn't behave as an acid in the typical sense, their presence and interactions in solution can influence the overall acidity or basicity.

 

[Borek]

When sodium ion (Na⁺) is dissolved in water, it does not directly act as a base by accepting a proton (H⁺) from water. Instead, sodium ion remains as Na⁺ and does not participate in proton transfer reactions. Its behavior is more characteristic of a spectator ion in solution, meaning it doesn't actively participate in the chemistry of the solution.

No.

In the water solution Na⁺ participates in the reaction

Na⁺ + OH^- ↔ NaOH

with a known equilibrium constant (technically stability/formation constant, as this reaction is typically listed not as an acid/base reaction, but complexation). For NaOH K_f is around 0.6 (this value will differ in different sources, but it is not far from 1 in general).

Thing is this reaction is indistinguishable from the base dissociation reaction (just reversed). This means K_b of around 1.6 - so not that high.

On the other hand, chloride ion (Cl⁻) can indirectly influence the acidity of a solution. When chloride ion is dissolved in water, it does not directly donate a proton like an acid. However, its presence can affect the pH indirectly. Chloride ions are conjugate bases of strong acids (such as HCl), meaning they can accept protons under certain conditions. In the presence of a strong acid, chloride ions can react with protons to form the weak acid, HCl. This reaction can shift the equilibrium of other acid-base reactions in the solution, effectively influencing the pH.

With HCl dissociation constant in the range of 10⁵ (again, different sources give different values, it is very difficult to measure it precisely) it is many orders of magnitude stronger as an acid than NaOH is as a base. That in turn means presence of Cl^- has much, much lower effect on pH than presence of Na⁺.

Sadly, most General Chemistry books repeat ad nauseam "NaOH is a strong base dissociated completely" ignoring the facts.