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    Can any one please explain me why the answer to the following question is A and if my concept is right or wrong? 😔

    - An aqueous solution of ethanoic acid is gradually diluted. Which of the following statements is *incorrect*?
    A- the pH decreases
    B- the value of Ka is unchanged
    C- the concentration of ethanoic acid molecules decreases
    D- the proportion of ethanoic acid molecules which dissociates increases

    Now what I understood was..that as water is added to ethanoic acid, the dissociation of the acid increases hence the equilibrium shifts to right producing more of Hydrogen ions and this would cause pH to decrease..
    CH3COOH + H20 <---> CH3COO- + H+ (The equation is not given in question, i wrote it myself)

    But that's not correct apparently.
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    (Original post by Tara1208)
    Can any one please explain me why the answer to the following question is A and if my concept is right or wrong? 😔

    - An aqueous solution of ethanoic acid is gradually diluted. Which of the following statements is *incorrect*?
    A- the pH decreases
    B- the value of Ka is unchanged
    C- the concentration of ethanoic acid molecules decreases
    D- the proportion of ethanoic acid molecules which dissociates increases

    Now what I understood was..that as water is added to ethanoic acid, the dissociation of the acid increases hence the equilibrium shifts to right producing more of Hydrogen ions and this would cause pH to decrease..
    CH3COOH + H20 <---> CH3COO- + H+ (The equation is not given in question, i wrote it myself)

    But that's not correct apparently.
    Hi,

    The questions asks for the answer that is incorrect. As you dilute ethanoic acid with water, the concentration of the acid decreases, thus the pH increases.
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    (Original post by VioletPhillippo)
    Hi,

    The questions asks for the answer that is incorrect. As you dilute ethanoic acid with water, the concentration of the acid decreases, thus the pH increases.
    The pH depends upon the concentration of Hydrogen ions, so how does pH increases? I mean like I said, diluting the acid would increase the concentration of hydrogen ions and so decrease the pH 😕
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    (Original post by Tara1208)
    The pH depends upon the concentration of Hydrogen ions, so how does pH increases? I mean like I said, diluting the acid would increase the concentration of hydrogen ions and so decrease the pH 😕
    Hi,

    Due to Le Chatelier's principle, as more water is added, the equilibrium will shift to the right to use up the water. So, more H+ ions will be produced, thus the pH would decrease.

    However, this is overruled by the fact that adding water to the acid will massively reduce its concentration and thus the number of H+ ions in solution. So, the pH imcreases. This is the principal that has the greatest affect and thus the one that is considered.
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    (Original post by Tara1208)
    diluting the acid would increase the concentration
    Forget for a second that this is even an acid.

    How could diluting something increase a concentration? (apart from of the solvent).

    1. By diluting it, you must decrease the conc. and hence raise the pH.
    2. Ka is only affected by T
    3. See 1.
    4. Only one left. CH3COOH + H2O <-> CH3COO- + H3O+. Apply Le CP.
 
 
 
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