A student is titrating 25.00 ml of a weak monoprotic acid solution with an unknown concentration. When setting up the experiment, the studen

Question

A student is titrating 25.00 ml of a weak monoprotic acid solution with an unknown concentration. When setting up the experiment, the student inadvertently uses another team’s solution of NaOH. The solution used has a lower concentration than the solution standardized by the student. Select all of the following statements that are true.
a) The pH at the equivalence point will be the same
b) The error will result in a calculated concentration that is higher than the actual concentration
c) You will be able to identify the acid based on the pka value that is determined from the titration curve
d) The pH at the 1/2 equivalence point will be the same
e) The titration will require less volume to react the equivalence point than if the student used their standardized solution

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Thạch Thảo 3 years 2021-08-13T13:47:34+00:00 1 Answers 6 views 0

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  1. kiet
    0
    2021-08-13T13:48:56+00:00
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    Answer:

    c) and d) are true

    Explanation:

    In this case, let’s analyze each statement and see if it’s true or not and why. All of this statements comes of the fact of what would have happen if you were not making the mistake, so you are comparing this case to the case that were supposed to be. Now let’s analyze the statements:

    a) pH at the equivalence point will be the same.

    As the concentration of the NaOH is lower than the one that you prepared, it means that we require more volume of this base to reach the equivalence point, therefore, the pH would be different (not so far but still different), so this stament is FALSE.

    b) Error result in a calculated concentration higher than the actual concentration.

    In this case, the concentration of the acid will not depend of the concentration of the base, because we have a monoprotic acid and a monoprotic base, so the relation between those in a mole ratio is 1:1. The only thing that is being affected is the required volume of the base to reach the equivalence point, but the concentration of the acid will be the same. So this statement is FALSE.

    c) Able to identify the acid based on the pKa value that is determined from the titration curve.

    In this case, even if we use a base with a lower concentration, the titration curve will not be affected and the pKa of the monoprotic acid will be the same. This is because pKa is related to the acid only, and is a constant value that tell us how strong an acid is, so no matter how much base we add, the pKa is constant and will not be affected. This statement is TRUE.

    d) The pH at the 1/2 equivalence point will be the same

    In all cases, when the titration is reaching the half equivalence point, pH will always be the same as the pKa. The only thing that changes is the required volume to reach that point. For example, with the standard base you prepared, it requires 10 mL while with the lower concentration base, we need 15 mL, but still, reach half the equivalence point so, the pH is the same as pKa. This statement is TRUE.

    e) Titration requires less volume to reach equivalence point.

    As it was stated in the previous cases, the base has a lower concentration, therefore, we will need more volume of base to reach the equivalence point and equals the mole of base and acid. This will only be true if the concentration is higher, but its not the case. The statement is FALSE.

    Hope this helps

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