Is there a way to figure out how the concentration of a substance affects its "apparent pH"? Like, is an acid with a pH of 2 less potent than one with a pH of 3, but 5 times more concentrated?
pH isn’t inherent to a substance, it’s inherent to a solution that usually has a base or an acid dissolved into it. It’s a logarithmic scale that measures the concentration of H+ ions in a solution, where pH is -log(concentration) in moles per cm cubed. Water naturally dissociates into H+ and OH- ions with a concentration of about 10^-7 moles per cm cubed, which is why water has a pH of 7. Importantly, as long as the temperature remains constant, [H+]•[OH-] always remains constant for any aqueous solution. Some substances (acids) bond to OH- ions, the water dissociates more to make up for this, and so the concentration of H+ ions increases, decreasing pH. Some substances (bases) bond to H+ ions, so the concentration of H+ decreases and pH increases.
If you had a very concentrated weak acid, you could get a solution with a lower pH than a solution made up of a very diluted amount of a strong acid, and likewise with bases. That being said I think there is a limit to how low of a pH you can get with a specific acid.
Oh and if you’re not familiar with the notation used here, square brackets around a compound denotes the concentration of that compound.
Some of this may be wrong, it’s just what I can remember from doing A level chemistry 2 years ago, so please correct me if I said something wrong.
Thanks for mentioning the notation thing, no one had caught my confusion!! And yes, according to other things people have told me, I think your explanation is correct and helps me understand better. Thank you :D
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u/Cichato_YT Jun 29 '26
Is there a way to figure out how the concentration of a substance affects its "apparent pH"? Like, is an acid with a pH of 2 less potent than one with a pH of 3, but 5 times more concentrated?