Midterm Q3-C

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MariahClark 2F
Posts: 60
Joined: Wed Nov 15, 2017 3:04 am

Midterm Q3-C

Postby MariahClark 2F » Sun Mar 17, 2019 1:11 am

Can someone please explain the reasoning behind the answer for Q3C on the midterm please, Im thinking way too hard.

sharonvivianv
Posts: 63
Joined: Fri Apr 06, 2018 11:05 am

Re: Midterm Q3-C

Postby sharonvivianv » Sun Mar 17, 2019 1:33 am

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)

sharonvivianv
Posts: 63
Joined: Fri Apr 06, 2018 11:05 am

Re: Midterm Q3-C

Postby sharonvivianv » Sun Mar 17, 2019 1:36 am

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+]

MariahClark 2F
Posts: 60
Joined: Wed Nov 15, 2017 3:04 am

Re: Midterm Q3-C

Postby MariahClark 2F » Sun Mar 17, 2019 1:51 am

Thank you so much!

Roberto Gonzalez 1L
Posts: 39
Joined: Fri Sep 28, 2018 12:17 am

Re: Midterm Q3-C

Postby Roberto Gonzalez 1L » Sun Mar 17, 2019 5:03 pm

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+].


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