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Adding NaOH to a weak base

  1. Sep 11, 2010 #1
    1. The problem statement, all variables and given/known data
    In my textbook, they dont necessarily explain what happens when we add a base to a weak acid (e.g. acetic acid)...so I was wondering if anyone can tell me if I got it down:

    -Like if we have acetic acid (which is a weak base) in water, it will form an equilibrium and form the hydronium ion (is this a strong conjugate acid?) and the acetate ion (strong conjugate base) as products.

    -If we add NaOH, this will dissociate into Na+ and OH-...the OH- being a strong base will likely react with the strong conjugate acid (hydronium ion) in order to negate the effects of the added base.

    -So essentially, this will favour the reverse reaction (does it bring it to completion since its a strong conjugate acid?)

    -In the end, the OH- that reacts with the hydronium ion will form water which doesnt affect the pH...?

    I dont really feel confident about my understanding though...it seems that I'm overthinking it...

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 11, 2010 #2


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    Staff: Mentor

    Let's call it a weak acid.

    When you add strong base it will neutralize the acid, you may assume neutralization was quantitative. There is always some hydrolysis of the conjugate base, at the same time acid left dissociates lowering pH. Safest way of calculating pH is to assume neutralization went to completion and use Henderson-Hasselbalch equation.

    When all acid has been neutralized (which means there is just a solution of sodium acetate) situation is dominated by hydrolysis, and you can calculate pH assuming you have a solution of a weak base (acetate).
    Last edited by a moderator: Aug 13, 2013
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