Why would HCl be considered an Arrhenius acid?

Answer 1

Technically speaking, acetic acid, when placed in water would dissociate a little to give you the conjugate base (the acetate anion) and a hydronium ion. So acetic acid is, by definition, an Arrhenius acid.

CH3COOH + H2O <<<---> CH3COO- + H3O+

HOWEVER, the equilibrium still favors the left side of the chemical equation because the hydronium ion H3O+ has a pKa of about -1.7 while CH3COOH has a pKa of about 4.8. pKa is a sort of intrinsic measure of an acid's ability to dissociate and protonate. The higher the pKa, the weaker the acid and the worse it is at dissociating. With those given pKa values, I can tell you that the hydronium ion is about 3 million times more acidic (i.e more able to give up a proton) than acetic acid. Therefore, we don't form very much H3O+. But we still do form a little bit of it so acetic acid is a weak Arrhenius Acid.

Acetic acid is an example of a carboxylic acid with the general formula of RCOOH.

These are weak acids. If we want for form their conjugate bases, we need a strong base, like hydroxide, for the deprotonation.

CH3COOH + OH- <--->>> CH3COO- + H2O

In this case, the equilibrium favors the right side of the equation because water (with a pKa of about 15.8) is a much weaker acid than acetic acid (still with a pka of 4.8). This makes acetic acid 100 billion times more acidic than water so obviously it's going to more easily give up its proton.

Sorry if this seems long-winded...acid/base chemistry is my favorite topic. (My research is focused on the formation of organometallic superbases).

Answer 2

HCl is considered an Arrhenius acid because it dissociates in water to produce hydrogen ions (H+ ions) in solution. According to Arrhenius acid-base theory, an acid is a substance that increases the concentration of H+ ions in an aqueous solution.

Answer 3

It produces H+ ions in solution.

Answer 4

It produces H+ ions in solution