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Acidity and Basicity confusion

Discussion in 'MCAT Study Question Q&A' started by Samchik, Aug 15, 2011.

  1. Samchik

    7+ Year Member

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    Hi,

    I have a problem with understanding why in organic chemistry species with a negative charge are called bases and species with positive one - acids, whereas in biology texts positive charge refers to basicity and negative charge to acidity.

    For example, from Wade 6th ed, Organic Chemistry: "An acetylide ion is a strong base and a powerful nucleophile".

    R-C≡C:-

    Also, an amine group is referred to as a basic group, because it has a pair of lone electrons on nitrogen.

    At the same time in biology texts phosphates in DNA are referred to as acidic (even though they have negative charge), and histones are referred to as basic (positive charge).

    I thought that a base is an electron donor, and therefore it should have a negative charge before reaction with acid.

    Do you have any idea how to distinguish between acids and bases with regard to their charges?

    Thank you in advance!
     
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  3. BilalL

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    Ok I think you need to understand Bronsted Lowry Acid Base vs Lewis Acid Base.

    Organic chemistry nucleophile/electrophile reactions follow Lewis Acid/Base chemistry where the nucleophile is the base which donates electrons to the electrophile( the acid).

    Gen Chem, and the phosphate example follow the BL acid / base theory, where the acid is the proton donor and the base is the proton acceptor.

    Phosphoric acid is triprotic(3 dissociable H's). So whether phosphate is an acid or base is determined by the conditions(acidic vs basic env) which determine its protonation state, and what its reacting with.

    So I would suggest looking up the phosphate buffer system in the blood. And also looking up the reasons for using Lewis vs BL and vice versa.
     
    #2 BilalL, Aug 15, 2011
    Last edited: Aug 15, 2011
  4. Samchik

    7+ Year Member

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    Thank you for clarification!
     

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