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Topic: Chemistry Unit  (Read 9097 times)

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Offline peterschmidt3943

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Chemistry Unit
« on: December 12, 2017, 12:10:59 PM »
Hello guys,

I have a question regarding the units of the following question:

What volume of a 0.10 mol dm–3 solution of NaOH is needed to neutralise 30 cm3 of a
0.20 mol dm–3 aqueous solution of a diprotic acid?


how can we translate dm^-3 into other units ? like, for example, in cm^3 or m^3?
« Last Edit: December 13, 2017, 03:53:36 PM by sjb »
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Offline Arkcon

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Re: Chemistry Unit
« Reply #1 on: December 12, 2017, 12:49:07 PM »
What do the units dm, cm, and for that matter, m stand for?
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #2 on: December 12, 2017, 12:52:50 PM »
decimetre, cenitmetre, metre...
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #3 on: December 12, 2017, 01:24:30 PM »
Ok, and a quick question regarding to the substance of the question:


a diprotic acid consists of the formula H_2 X ... why do I have to multiply 0,2mol dm^-3 times 2 ? I mean the question explicitly states that 0,2 mole OF sth... isnt the diprotic acid in total 0,2 mole dm^-3?


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Offline sjb

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Re: Chemistry Unit
« Reply #4 on: December 12, 2017, 01:45:23 PM »
Quote from: peterschmidt3943 on December 12, 2017, 01:24:30 PM
Ok, and a quick question regarding to the substance of the question:


a diprotic acid consists of the formula H_2 X ... why do I have to multiply 0,2mol dm^-3 times 2 ? I mean the question explicitly states that 0,2 mole OF sth... isnt the diprotic acid in total 0,2 mole dm^-3?

Yes, but what else is in your question. What is happening in your reaction?
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #5 on: December 12, 2017, 01:52:32 PM »
NaOH gets used up...
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #6 on: December 12, 2017, 02:01:29 PM »
Do you mean we need 4x NaOH because of the fact that we got a diprotic acid?

2*0,2=0,4
0,4/0,1=4
4*30=120...
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Offline Arkcon

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Re: Chemistry Unit
« Reply #7 on: December 12, 2017, 02:23:46 PM »
WHat is the NaOH doing?  What is it "used up" by?  Why does a "di" protic acid seem to "use up" twice the NaOH?
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #8 on: December 12, 2017, 02:24:55 PM »
That I do not know...
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #9 on: December 12, 2017, 02:25:36 PM »
It acts as a base, but I dont know why twice the amount is reacting...
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Offline Arkcon

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Re: Chemistry Unit
« Reply #10 on: December 12, 2017, 02:27:00 PM »
I hope you don't mind us answering your questions with more questions, but that's what we do here.  We try to help you learn to help yourself.  Its part of our Forum Rules{click}.  If you're still stuck, why not write out the whole problem, including what you've learned in this thread, all at one to see it all together.
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #11 on: December 12, 2017, 02:29:04 PM »
Well, I know that twice the amount of NaOH should react, and that would explain the solution (120cm^3)... but I don't know why twice the amount of NaOH reacts..
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Offline Borek

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Re: Chemistry Unit
« Reply #12 on: December 12, 2017, 03:36:54 PM »
Start with the reaction equation.

http://www.titrations.info/titration-calculation
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #13 on: December 12, 2017, 03:49:47 PM »
2NaOH + H2SO4 → Na2SO4 + 2H2O... (for example)
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Offline peterschmidt3943

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Re: Chemistry Unit
« Reply #14 on: December 12, 2017, 03:56:14 PM »
the mole ratio is 2:1, this explains it, right ?
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