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What is different about neutralization reactions that produce a neutral solution at the equivalence point and those that produce acidic or basic solution?

I think it is the concentration of the reactants?

  • Chem -

    No, its whether the anion, the cation, neither cation nor anion, or both cation and anion, hydrolyze.
    When an acid is neutralized with a base, it forms a salt and water at the equivalence point. For example,
    HCl + NaOH ==> NaCl + H2O
    Since neither the Na^+ nor the Cl^- are hydrolyzed the solution is neutral.

    But if you have acetic acid (CH3COOH) neutralized with NaOH it is
    CH3COOH + NaOH ==> CH3OONa + H2O.
    The Na^+ is not hydrolyzed but the acetate ion is as follows:
    CH3COO^- + HOH ==> CH3COOH + OH^- and since the OH^- is freed it is basic.

    For NH3 + HCl ==> NH4Cl, the Cl- is not hydrolyzed but the NH4^++ is as follows:
    NH4^+ + H2O ==> NH3 + H3O^+ and this solution is acidic because of the freed hydronium ion.

    For a weak acid + weak base such as
    acetic acid + ammonia you have
    CH3COOH + NH3 ==> CH3COONH4 and both are hydrolyzed with the total equation being the sum of the two respective ones above. In this case the Ka for acetic acid is the same as Kb for NH3 so the solution is neutral; however, it will be acidic if Ka is larger than Kb or basic if Kb is greater than Ka.
    Hope this helps.

  • Chem -

    Oh, such a big help! Thank you!

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