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Topic: concentration at equivalent point  (Read 3135 times)

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Offline emissivity

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concentration at equivalent point
« on: December 01, 2012, 07:20:20 AM »
analyte : 0.2M NH4OH     :rarrow: 20mL

titrant : 0.1M HCl

Calculate the concentration of NH4OH(or NH3) in solution at equivalent point.




============================================================

I used
0.2M × 20mL    =    0.1M × xmL
x=40mL


its initial concentration is 0.2M
its initial volume is 20mL
its final volume is 20+40mL = 60mL


So NH4OH 's concentration is

0.2M × (20mL/60mL)

=0.2/3

=0.067M

is this right?

I don't know how to calculate this..

help me..

Offline Borek

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Re: concentration at equivalent point
« Reply #1 on: December 01, 2012, 07:28:01 AM »
You correctly took care of the dilution, but you forgot NH3 reacts with the acid - so it is not only the dilution, but also an acid-base equilibrium.
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Offline emissivity

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Re: concentration at equivalent point
« Reply #2 on: December 01, 2012, 07:59:12 AM »
You correctly took care of the dilution, but you forgot NH3 reacts with the acid - so it is not only the dilution, but also an acid-base equilibrium.


How can I consider acid-base equilibrium?
I totally don't know how to start it..

Actually I don't even understand why the problem gave me NH3 as well as NH4OH..

Offline Borek

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Re: concentration at equivalent point
« Reply #3 on: December 01, 2012, 08:30:36 AM »
NH3 and NH4OH are basically the same thing, just written differently. Some say ammonia in water solutions is present just as NH3, some say it is present as NH4OH. It doesn't matter for most practical purposes.

What is the reaction taking place during titration?
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Offline emissivity

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Re: concentration at equivalent point
« Reply #4 on: December 01, 2012, 10:09:03 PM »
NH3 and NH4OH are basically the same thing, just written differently. Some say ammonia in water solutions is present just as NH3, some say it is present as NH4OH. It doesn't matter for most practical purposes.

What is the reaction taking place during titration?



NH4OH + HCl  :rarrow: NH4Cl + H2O

but next I don't know..  :'(

Offline Borek

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Re: concentration at equivalent point
« Reply #5 on: December 02, 2012, 04:47:38 AM »
OK, so what is the substance present in the solution at the equivalence point?
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