Arrhenius' theory


 

What was Arrhenius’ theory?

Throughout history many chemists have tried to identify the difference between acids and bases. The two substances had in the seventeenth century already been labeled according to some characteristics, by the Irish writer Robert Boyle. Acids have the characteristics of tasting sour, being corrosive to metals, changing litmus paper red and becoming less acidic when mixed with bases. Bases have the characteristics to feel slippery, change litmus blue, and they become less basic when mixed with acids.

 

While people tried to find the explanation of why acids and bases behave the way they do, the first reasonable definition of acids and bases would not be proposed until approximately two hundred years later after the characteristics Boyle had them labeled. In 1838 a German chemist, Justus von Liebig defined acids a bit closely, having the theory saying that “acids were substances that can react with metals to produce hydrogen gas”. Forty-six years later, in 1884, Liebig’s statement got followed by the Swedish chemist called Svante Arrhenius, theory. Arrhenius’ theory was the first comprehensive theory of acids and bases.

 

According to Arrhenius the acid solutions contained many ions due to being electrolytes. Svante Arrhenius proposed that water can dissolve many compounds by separating them into their individual ions. As already mentioned in our introduction, Arrhenius’ theory said that acids are substances which produce hydrogen ions (H+) in solution (called Arrhenius acids) and bases are substances which produce hydroxide ions (OH-) in solution (Arrhenius bases). Due to this it was recognized that water has an important role in the acidity of a substance. To determine if something was acidic or basic one 

looked at the concentration of the hydrogen ion or the concentration of the hydroxide ion.


Not only did Arrhenius’ theory identify what ions are to be produced when an acid or a base is dissolved in water, but it as well said that the reason of why acids have the same characteristics (which as mentioned already, Robert Boyle had labeled) was due to that the fact that they all are proton (hydrogen ion) donors. His theory also proved that whenever acids and bases react, they are neutralized and form water. This occurs as the acids will produce hydrogen ions whereas the bases will produce hydroxide ions.
Arrhenius’ theory of acids and bases was able to explain several phenomenons such as the process of neutralization. Neutralization happens because hydrogen ions and hydroxide ions react to produce water.

Substance:

Ion produced when substance is in solution:

Acid

Hydrogen ion, H+

Base

Hydroxide ion, OH-

The chemical equation of the produced ions reacting together:

H+ (aq) + OH-(aq) à H2O (l)

If one were to conclude Arrhenius’ theory as straightforward as possible, one could simply say that acids are proton donors and bases are hydroxide donors.

Examples of how several Arrhenius acids dissociate in water:

HCl (aq)à H+ (aq) + Cl-(aq)

HBr (aq)àH+(aq) + Br-(aq)

Since acids are according to Arrhenius a substance that dissociate in water to produce one or more hydrogen ions, H+, HBr is an acid.

H2SO4 (aq)àH+(aq) + HSO4 (aq)

HClO4 (aq)àH+(aq) + ClO4-(aq)

As one can see on all the examples above of the dissociation of Arrhenius acids, a hydrogen ion will always be dissociated.

Examples of how several Arrhenius bases dissociate in water:

NaOH (aq) à Na+ (aq) + OH-(aq)

LiOH (aq) à Li+ (aq) + OH-(aq)

KOH (aq) à K+ (aq) + OH-(aq)

Ba (OH)2 (aq) àBa+2 (aq) + 2OH-(aq)

Once again, in all of these cases all the bases will dissociate the hydroxide ions

Subpages (1): Limitations
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