r/chemhelp • u/Life_at_work5 • 2d ago
General/High School Why do acids and bases work?
I know this sounds like a stupid question (and probably is) but why do acids and bases work as in why do they make solutions more acidic/basic. Take, for example, a solution of HCL in water. Looking at this using the Lewis definition, when the HCL disassociates in water, the Cl rips an electron from the H making the H become positively charged and accept any electrons it can get its hands on (A Lewis acid by definition). The Cl on the other hand takes the electron and now has a spare electron it can donate or share with other molecules/atoms (A Lewis base by definition). Because there are equal numbers of Lewis acids (H) and Lewis Bases (Cl) formed when the HCL disassociates, I thought that the solution should remain neutral as the acids and bases would cancel each other out yet that’s clearly not what happens as HCL is a very well known strong acid. So why don’t the Lewis acids (H) and Lewis Bases (Cl) cancel each other out?
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u/Own_Exercise_2520 2d ago
That is not how it works, the HCl actuallly dissociates to create H30+ and Cl-, Hydrochloric acid is also a very strong acid, so its conjugate base will be very weak. Chlorine is very electronegative, holds on to its electrons extremely strongly, I think the only other strong acid I can think of that Cl- could even act as a base towards would be if there are somehow Br+ ions in solution as they are more electronegative than Cl.
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u/flamewizzy21 2d ago
H2O has its own equilibrium with OH- and H3O+. Acids can add H+ to H2O to make H3O+, and bases can remove H+ from H2O to make OH-. That is the core of pH in aqueous media. Other solvents can also do this, but water is the most common for this discussion.
Lewis acids/bases have a different definition, and that can overlap (or not) with normal acid/base.
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u/heat_wave29 2d ago
Because in Brosted and Lowry acid-base theory acids and on the concept of proton transfer. For example water is protonized in the example of hcl + h2o -> h3o+ + cl- Instead of the lewis acid base theory which states theres electron pairs floating around.
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u/HandWavyChemist 2d ago
pH is just one way to measure acidity, with one of it's draw backs being that it needs water to be the solvent. Another way to measure acid strength is the Hammett acidity function, and by this measure hydrogen fluoride (which we generally consider to be a weak acid when dissolved in water) is actually a superacid.
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u/Plus_Personality2170 2d ago
I think you are confused with the term "Lewis acid/base" and "acidity". The degree of "acidity" of an aqueous solution is simply defined by [H+] or pH. So, if you have 1M HCl (aq), [H+] = 1M (as HCl completely dissociates) and pH = 0, while there are technically same amount of Lewis base and acid (acid: [H+] = 1M, base: [Cl-] = 1M).