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About Sodium Carbonate(Definition of base)

  1. Apr 27, 2010 #1
    A base is a chemical which reacts with an acid forming water and salt only.
    Is this definition of base true?
    If true, metal carbonates are not considered as base (carbon dioxide is also formed during neutralization which violates the definition). Hence, the solution of metal carbonates are not considered to be alkalis (since alkali is a subset of base). However, metal carbonates are usually basic, e.g. sodium carbonate. I am bewildered whether we can call sodium carbonate a base then.
    Moreover, I would like to know the chemical reaction of sodium carbonate representing the production of OH- ions. Thanks very much.
     
  2. jcsd
  3. Apr 27, 2010 #2

    alxm

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    Science Advisor

    Arrhenius base: A substance which increases the amount of hydroxide ions when added to an aqueous solution.
    Brønsted-Lowry base: A substance which can act as a proton acceptor.
    Lewis base: An electron-pair donor.

    Those are the most common, and the Brønsted-Lowry is probably the most used and the one implied by 'base' in general.
     
  4. Apr 27, 2010 #3
    So, is sodium carbonate considered a base?
     
  5. Apr 27, 2010 #4
    It's a Brønsted-Lowry base.
     
  6. May 15, 2010 #5
    I find that definition true. There's really nothing complicated or more in-depth from the question. Bases are involved in neutralization reactions, which does product water and salt.
     
  7. May 16, 2010 #6

    Borek

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    Staff: Mentor

    So, how do you explain high pH of solution of ammonia, or of solution of carbonate, or of solution of phosphate?

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  8. May 16, 2010 #7
    Well, all follows from the definition of base we're using. Sodium carbonate isn't a Arrhenius base, but it is a Bronsted-Lowry.

    @Borek: I agree with Trooper100. Low pH of ammonia solution can be explained since NH3 acts as a proton acceptor. Low pH of phosphate and carbonate solutions are explained by the hydrolysis of the phosphate and carbonate ions.
     
  9. May 16, 2010 #8

    Borek

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    I can be misreading something, but Trooper has just confirmed initial definition from the very first post:

    Now combining it with your post:

    Basically you have stated "base is a chemical that reacts with acid forming water and salt, but ammonia solutions are basic because ammonia reacts with water". Second part of what you stated can be not explained using definition you have listed first.

    It is not that Arrhenius definition is incorrect, it is just limited and original question can be not answered using it.

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