Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: johnsmith123 on November 04, 2016, 07:22:40 PM
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Need help on this question.
50.00 mL of an aqueous solution of which is 0.0500 M in ethylenediamine is mixed with 10.00
mL of an aqueous solution which is 0.400 M of perchloric acid. Calculate the pH at equilibrium.
Ethylenediamine Kb,1 = 4.33 x 10 -4
Kb,2 = 7.04 x 10 -8
Chlorous ka: 1.12 x 10-2
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what kind of substance is ethylenediamine ? and what about perchloric acid ?
what will happen if you mix those two?
taking into account the amounts/conc. mentioned, what kind of system will result here? what formula belongs to those systems?
hint: the acid mentioned in the text ( HClO4) doesn't match the ka given below , as the ka given belongs to another acid (HClO2)
regards
Ingo
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I understand that this is an acid base reaction with hclo4 being a strong acid and ethylenediamine being a weak base. by mixing the two a strong base and weak acid will form with unknown conc. of x at equilibrium. i just do know where to start when given the initial conc. of both the initial acid and base
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Hint: find the limiting reagent.
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(...) by mixing the two a strong base and weak acid will form with unknown conc. of x at equilibrium. (...)
no: the reaction of the (super-)acid HClO4 will lead to an ultraweak base ( i.e. ClO4- , considered to be so weak that you can treat it as neutral, for all practical purposes)
the part with "weak acid" (resulting from ethylene diamine) is correct, however.
hint: what does ethylenediamine mean, i.e. how much base is there around initially?
compare this to the initial amount of acid around!
what kind of system will result?
regards
Ingo
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I understand that this is an acid base reaction with hclo4 being a strong acid and ethylenediamine being a weak base. by mixing the two a strong base and weak acid will form with unknown conc. of x at equilibrium. i just do know where to start when given the initial conc. of both the initial acid and base
We still do not know which acid you use: HClO4 or HClO2.
Please, explain.
Follow Borek advise and calculate stoichiometry of neutralization (with limiting reagent). In stoichiometric calculations (in both cases) assume no equilibrium.
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Thank you for the responses. Hclo4- is being used. I used the tips and i found oh- at equilibrium to equal .00104 mol using an ice table and the H+ conc. to be .004 mol. So .004 - .00104 = .00296 mol. I then found the conc. by .00296mol/.06 L and i took the -log of that and got 1.31 as the pH. Is that the correct answer?
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(...) Is that the correct answer?
no
... and frankly speaking, neither do I understand what you've been calculating, nor do I understand you approach in general
you have a strong acid (and a certain amount thereof), you have a two-stage weak base (with, again, a certain amount thereof)
start by figuring out what will happen, and to what degree
after that, pls. come back with a detailled calculation of the resulting situation, so we can move further from there
regards
Ingo
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alright i think i got it. I just want to know if the answer i got is correct. Is it 12.4?
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disregard the last one, i actually got the answer to be 7.32, is this correct?
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no
regards
Ingo
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Show your stoichiometry in details.