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In this question the answer key given is A and C. But i think that D should also be wrong because equivalents = molecular mass / n factor = $\frac{90}{2} = 45 \neq 40 $

I believe I am correct but I may be wrong so can someone please help me clarify my question.

  • 4
    $\begingroup$ The reaction (ii) is incorrectly enumerated in the first place. The wording of (D) does not make sense and the whole question has inferior quality. $\endgroup$
    – Poutnik
    Apr 26 '19 at 18:17
  • $\begingroup$ +1 for the OP bringing a problematic question here and asking for guidance. I can't understand the down vote. $\endgroup$
    – uhoh
    Apr 27 '19 at 2:06

I agree with Poutnik's point that this is a poor question.

Oxalic acid has two acidic protons so its equivalent weight is $\frac{1}{2}$ its molecular weight. Thus:

  • Answer A is false.
  • Answer B is true.
  • Answer C is false since there are 2*100*0.2 = 40 milliequivalents of acid, but only 100*0.2 = 20 milliequivalents of base.

Answer D requires some extra work. First it is not clear if Answer D applies to both reaction (i) and reaction (ii)

  • For reaction (i), in 100 ml of 0.2 M oxalic acid there are 40 milliequivalents of acid

  • For reaction (ii), the reaction is a redox reaction, so the number of electrons exchanged by oxalic acid needs to be determined.

    Here is another sloppy point about the question. Reaction (ii) is not balanced.

    However to figure out the number of electrons exchanged by oxalic acid, we only need the half cell reaction which is:

$\quad\quad\ce{2CO2(g) + 2 H+ + 2e− <=> HOOCCOOH(aq)}$

$\quad\quad$ Since oxalic acid exchanges two electrons in the redox reaction, its "redox" equivalent
$\quad\quad$ weight is $\frac{1}{2}$ its molecular weight.Thus there are also there are 40 milliequivalents of
$\quad\quad$ oxalic acid redox wise too.

  • Answer D is false, because there are 40 milliequivalents of oxalic acid, not 40 equivalents
  • 1
    $\begingroup$ Answer D is true only if it states that "milliequivalents of oxalic acid in..." $\endgroup$ Apr 26 '19 at 21:08
  • 1
    $\begingroup$ @MathewMahindaratne - Thank you for the correction. I fixed the answer. $\endgroup$
    – MaxW
    Apr 26 '19 at 21:10
  • $\begingroup$ Okay but isn't oxalic acid's meq = 45 because 90/2 @MaxW. $\endgroup$
    – TheChemist
    Apr 27 '19 at 1:39
  • $\begingroup$ @user198885 - No, 100 ml of 0.2 molar solution is 20 millimoles of oxalic acid. In a redox reaction because there are 2 electrons per molecule of oxalic acid that is 40 milliequivalents of oxalic acid. Answer D refers to 40 equivalents not 40 milliequivalents. $\endgroup$
    – MaxW
    Apr 27 '19 at 4:45

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