Why is citric acid so sour despite it being apparently a weak acid?
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How do we know sulfuric acid isn’t sour?
It’s a “weak acid” in the chemistry sense – meaning that it doesn’t fully dissociate (into H+ ions and its conjugate base) in an aqueous solution. A fruit or juice high in citric acid can still have a pretty low pH with respect to what your body can handle. Drinking a strong acid like sulfuric would burn your digestive tract, unless it’s a very dilute solution.
Also, our sour taste buds aren’t really tasting the pH. How tart something tastes has more to do with its “titratable acidity” – which is basically a measurement of how many individual acid molecules there are, regardless of their dissociation state.
The perception of sour taste is not a direct measure of the pH. It is not the case that the more acidic something is, the more sour it is.
“weak” is relative.
Citric acid, a weak acid, tastes really sour.
Nitric acid, a strong acid, dissolves your tongue.
Also “weak acid” / “strong acid” is a specific chemistry term describing whether an acid fully dissociates into H+ and [acid]- ions in solution (strong) or if only a certain % of acid molecules dissociate and then reach an equilibrium (weak). It’s not using “weak” and “strong” in their normal non-science definitions. When something is a “weak acid” we’re not saying it’s weakly corrosive or weakly sour, only saying it doesn’t 100% dissociate in solution. There are “weak acids” that are *extremely* corrosive and dangerous, that you definitely could not even eat like you can with citric.
Meanwhile ascorbic acid (vitamin C) tastes bitter. It’s a case of concentration, strength (pKa) and how the taste nerves react to the acid as a whole.
Think about if you had a very neat and sorted toy chest. Everything is in place, and everything is organized.
Now, your mom decided to have a play date with that bratty kid down the street, Jeffrey. She invites him over and he brings his toys. Unfortunately, out of his hundred toys, he has 20 of the same toy. Let’s say it’s a Stretch Armstrong. and he doesn’t like that toy very much.
Stretch Armstrong is a *hydrogen ion*. When Jeffrey sees toys that interest him, he takes them from your toy chest and throws his boring Stretch Armstrong away, scattering them throughout your room.
That’s what happens when an acid comes into contact with something it reacts to. Since Jeffrey has a lot of stretch armstrongs, he’s going to take a lot of stuff and in the process he’ll be losing his stretch armstrongs.
Those stretch armstrongs, aka hydrogen ions, make the “sour” feeling in your mouth, aka your room.
Now let’s say your mom invites a nicer kid over, say their name is Lucy. Lucy has one Stretch Armstrong, and trades it to you for a furby. Lucy doesn’t have a lot of hydrogen ions to lose. Lucy is a weaker acid, say the acidic acid in a cucumber. Cucumbers are acidic, but only mildly so.
Now your mom invites a deranged maniac named Billy over. He has a million stretch armstrongs, and after he’s emptied out your toy chest he starts taking everything else in your room. Your bed, your lamp, your walls, your house, even your mom. You’re left with nothing but a pile of Stretch Armstrongs. Billy is a strong acid, and your house is your face after you decided to drink hydrochloric acid.
Have you ever tasted a strong acid? It’s so much worse.
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