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Midterm Q3-C

Posted: Sun Mar 17, 2019 1:11 am
by MariahClark 2F
Can someone please explain the reasoning behind the answer for Q3C on the midterm please, Im thinking way too hard.

Re: Midterm Q3-C

Posted: Sun Mar 17, 2019 1:33 am
by sharonvivianv
Partial Answer:
[HA] = 0
can't be true because they gave you [HA] in the problem already
[HA] = Ka
can't be true because of the relationship between pKa and Ka (pKa = -logKa)

Re: Midterm Q3-C

Posted: Sun Mar 17, 2019 1:36 am
by sharonvivianv
If you write the equation out you get

HA +H2O -> A- +H3O+

you know that A- and H3O+ concentrations are equal to x and [HA] was 0.1-x so it can't be

[HA]=[H3O+] or [HA]=[A-]

so the answer is [HA] can't equal [H3O+]

Re: Midterm Q3-C

Posted: Sun Mar 17, 2019 1:51 am
by MariahClark 2F
Thank you so much!

Re: Midterm Q3-C

Posted: Sun Mar 17, 2019 5:03 pm
by Roberto Gonzalez 1L
Given that pKa=10 , and that it is a weak acid, an amount x is ionized so there is an x amount of hydronium. However being that HA is a weak acid the amount ionized is very small compared to [HA] therefore it cannot equal [H30+].