Is curdling a chain reaction?

Question

Or, like in some other reactions, will the reactants get used up if there aren't enough, and the curdling stop? like, if the milk is just introduced to a tiny but adequate amount of acid to start the curdling, will all of the colloids come out of suspension because the pH stays adequately acidic? does curdled protein have an alkalinic effect?

could you give an example of a *curdling* reaction where i can see the reactants change into the products? does the H+ atom combine with the protein? so that there isn't a free H+ anymore?

one way to observe my question is to use the melting of ice as a metaphor.

the heat enters the ice-water mixture, and instead of seeing the temperature raise, we see the ice melt and melt until there is no ice and then the temperature can then increase.

if we add acid to milk in small quantities, will the milk curdle in small quantities at a constant pH until all the available proteins have curdles--and then only would the pH begin to drop again (as we continue adding parcels of acid)?

Answer 1

I wouldn't refer to curdling as a chain reaction. I commented on this in an earlier version of this question, but now I see you are seeking additional details. Here is what I know about the process (and I'm certainly no expert).

Curdling of milk occurs when the milk is acidified because the proteins (mainly casein) unfold (become denatured) and then are attracted to each other and clump together and this is what we see as curdling. Once the casein is denatured, it does not go back to its normal folded state and so the curdling persists. After the casein (and probably other proteins) have clumped together, the process stops, but the milk is still curdled. I have no idea what you mean by an "alkaline effect", so I can't address that question.

An example of a reaction where you can see reactants change into products might be something like mixing a solution of salt (NaCl) with a solution of silver nitrate (AgNO₃). Both are clear and colorless, but upon mixing, you see it turn milky white and then a solid white precipitate occurs.

NaCl(aq) + AgNO₃(aq) ==> NaNO₃(aq) + AgCl(s)

As for you final question about do the H⁺ ions combine with the protein, the answer would, in a sense, be yes. If you consider the folding nature of the protein to be partly a result of salt bridges and/or disulfide bonds, then the H⁺ sort of neutralizes these attractions by combining with one or the other or both. But, there are so many more H⁺ ions in an acidic solution than there are protein sites, that there will still be plenty of free H⁺ ions. Hope this answers your question.