A Carbon skeleton with 2 diff functional groups

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Discussion Overview

The discussion revolves around the concept of a hydrocarbon skeleton with two different functional groups and their relationship to pH and electrical charge. Participants explore the implications of pH on the charge of molecules with multiple functional groups, particularly in the context of amino acids and zwitterions.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that for a molecule with two functional groups, the pH must fall within a specific range to be electrically charged, proposing that pH will be between 6 to 7 and 9 to 10.
  • Another participant challenges the notion of a functional group having a characteristic pH, stating that pH refers to the activity of H+ ions in solution and varies with concentration.
  • A third participant emphasizes that a molecule is uncharged by definition and that pH does not determine electrical neutrality, noting that the behavior of molecules with multiple functional groups depends on various factors such as temperature, solvent nature, and concentration.
  • One participant introduces the concept of zwitterions, particularly in the context of amino acids, indicating that they can be positively charged, negatively charged, or neutral depending on pH.
  • A later reply acknowledges the possibility of discussing zwitterions and expresses regret for not considering that aspect earlier.

Areas of Agreement / Disagreement

Participants express disagreement regarding the relationship between pH and the charge of functional groups, with some asserting that functional groups do not have a characteristic pH and that pH is not directly related to electrical neutrality. The discussion remains unresolved with multiple competing views presented.

Contextual Notes

Participants note that the behavior of molecules in solution is influenced by various factors, including temperature, solvent, and concentration, which complicates the relationship between pH and charge.

nemzy
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Lets say for example a hydrocarbon skeleton has two diff functional groups branched to the skeleton.. Let's say one of the functional groups pH is less than 9 to 10, and the other functional group's pH is greater than 2 to 4

that means that molecule to be electrically charged, the pH of the molecule has the be true for both of the pH of the functional groups right?

so pH will be (6 to 7) < pH < (9 to 10)

correct me if I am wrong

thanks
 
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What do you mean by Ph of a functional group? Ph is used to refer to the activity of available H+ ions. As the activity of H+ differs in each solution depending on concentration there can be no Ph of a functional group.
 
First of all, a molecule by definition is uncharged. A functional group does not have a characteristic pH. As a concrete example, ethanol and propanol have different values of the dissociation constant because of a difference in their structure even though both have an identical hydroxyl group. There are countless other examples, which necessitate a correct explanation.

Secondly, pH has nothing to do with electrical neutrality here.

If you have a molecule which has multiple functional groups, its behavior in solution where it can ionize will depend on

(a) temperature
(b) nature of solvent
(c) concentration of the molecule (the solvent for practical purposes)

Generally the more acidic group (or more basic group as the case may be) predominates (suppose some molecule is a hydroxy acid...the hydrogen of the carboxyl group will be more easily lost due to subsequent stabilization of the anionic species). Note that pH in solution still depends on the total hydronium ion concentration in solution and not on just one functional group. (The acid dissociation constant, concentration and ion product of water at the particular temperature are some of the things you need to know to mathematically compute pH to a certain degree of theoretical accuracy.)

Cheers
Vivek
 
He may be talking about Zwitter ions.Say i amino acids,it may be +vely charged -vely charged or may be neutral according to pH.
 
poolwin2001 said:
He may be talking about Zwitter ions.Say i amino acids,it may be +vely charged -vely charged or may be neutral according to pH.

Yes I am sorry I didn't consider that.
 

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