Is strength of an acid proportional to concentration or dilution?

Question

I have a confusion between two seemingly contradictory factors.

Since pH =-log[H+], it suggests that more the concentration of the acid, lesser will be its pH, and therefore the stronger it is. But, according to Ostwald's dilution law, the degree of dissociation of an electrolyte is directly proportional to the square root of dilution. Though this exact relationship is true only for weak electrolytes, I believe that the degree of dissociation of any electrolyte would increase with dilution, keeping the temperature constant. And, more the degree of dissociation, more would be the H+ions released, and stronger the acid.

Where am I wrong in my reasoning? Thanks in advance.(Please give me an answer and not just a comment)

Answer 1

Is strength of an acid proportional to concentration or dilution?

This is an interesting question. It is sort of like being asked "What is your size?". If you are buying shoes then size means one thing, yet it is something different if you are buying pants.

So there are two different "strengths."

Strength can mean how much acid is present. So per unit volume of solution, a solution with 50% concentration has half the strength of the 100% concentration.

Strength can also mean how acidic, in terms of pH, would a specific solution be if the acid concentration were kept constant. In this sense hydrochloric acid is a stronger acid that acetic acid.

So the gist of your problem is that you're trying to draw a comparison between two different uses of the word strength when such a comparison is pointless.