CHRIS25
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A 1 mole HCl question
OK, this has to be a simple question with a simple answer, but hey guess what? Mmm not for me, as usual.
I titrated my CuCl etchant before and after. It now has a free HCL molarity of 1.38,
I wish to make it 2.38mol. So I cleverly? made a 200mL solution of a 1 mole HCl concentration and was about to add it to my 2 Litres of CUCL. Until
I suddenly hit myself (Softly) and realised that if I do this then I am actually only adding 0.0005mol to my solution because it is 2 litres.
So I need to make 1mol as if I was preparing a 1mol HCl solution for 2 litres of water? In other words I need to add 186mL of concentrated HCl to my
CUCl etchant in order to bring it up from 1.38 to 2.38mol approx.
Ok I think this is a dumb question, but still shaky on the old foundations, but definately getting there.
Am I right? thanks
[Edited on 19-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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Magpie
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Edit: You need to tell us the molarity of your HCl. I assumed 12M for the calculation below.
Instead of answering your questions directly I'll show how I would have done it:
Given: 2 liters of etchant 1.38M in HCl
assume 12M HCl available
Desired: bring etchant to 2.38M in HCl
I'm sorry Chris, but algebra really is useful in such calculations, so I'm going to use it.
Let V = the volume of 12M HCl to be added
then (V + 2000 mL) (2.38M) = (2000mL)(1.38M) + V (12M)
2.38V + 2000(2.38) = 2000(1.38) + 12V
2.38V + 4760 = 2760 + 12V
9.62V = 2000
V = 2000/9.62 = 208 mL
If you look at the 1st equation above you will see that it is nothing more than an HCl material balance.
[Edited on 19-7-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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CHRIS25
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Hi magpie, well it is certainly not something I would have thought of, but everything was fine until this:
2.38V + 4760 = 2760 + 12V I juggled around for 6 minutes and still this bit makes no sense to me: 2.38 x v + 4760 ??How do you arrive at 9.62?
Like wise the 2760 + 12 x v = 2000 ?? Adding and multiplication is really a basic, but this defies all of my understanding.
Secondly why then is my figure of 186mL wrong, being, as I understand things thus far, this is a 2mol solution of HCl if added and topped up to 2000mL
of water.. Perhaps if I understand where I am wrong I might be able to better comprehend that algebra.
EDIT: I have a 12mol solution of HCl. or 11.65 as some have it, don't know who is correct here. Also it is not the etchant that I measured for
molarity it is the amount of free H+ ions from the HCl in the etchant that is being measured, Just making sure because you said:...2litres of etchant
in HCL but I might be misunderstanding your wording..
[Edited on 19-7-2012 by CHRIS25]
[Edited on 19-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
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Mood: Chemistry: the subtle science.
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This is simply the mathematical reduction of the 1st equation.
12-2.38 = 9.62
I didn't state that.
Quote: Originally posted by CHRIS25  |
Secondly why then is my figure of 186mL wrong, being, as I understand things thus far, this is a 2mol solution of HCl if added and topped up to 2000mL
of water.. Perhaps if I understand where I am wrong I might be able to better comprehend that algebra.
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If you topped off 186mL of 12M HCl to 2000 mL the molarity would be = (0.186 liter)(12M)/2 liter = 1.116M
| Quote: Originally posted by CHRIS25 |
EDIT: I have a 12mol solution of HCl. or 11.65 as some have it, don't know who is correct here. Also it is not the etchant that I measured for
molarity it is the amount of free H+ ions from the HCl in the etchant that is being measured, Just making sure because you said:...2litres of etchant
in HCL but I might be misunderstanding your wording..
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A 12M solution of HCl is 12M in H+ for your purposes.
I can't teach you algebra in one lesson. You'll have to take my word for it and use it as a template if you wish. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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CHRIS25
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Thanks magpie, that was what I wanted to do - use as a template, but it helps to understand things,
When I see something like this: 2v or 3y it always means 2 x V or 3 x Y hence the confusion with your 12v, which I still don't get,
2.38V + 4760 = 2760 + 12V
9.62V = 2000 ??? Means to me 9.62 x V = 2000, so how when you say 12 - 2.38 = 9.62 I had already noticed that but that answer made no sense...Have no
clue what is going on here then, and yes I sympathize with you, you don't have to teach me algebra.
It makes no sense so I guess I will have to leave it. I guess after titration I will do it the 12th century way - add a superfluous and subjective
amount of concentrated HCl and then take another titration before and after and calculate differences over weeks and then I will have a good idea of
what to add.
There is only a certain amount of maths that I can cope with and no more, there is too much learning here. Thankyou for your help though, thought it
was an uncomplicated issue that I was asking....Gulp!
[Edited on 19-7-2012 by CHRIS25]
I got it, after much head scratching. You crossed over. Ie + changes to - in 4760-2760. ok makes sense now. As for the difference between your 208
mL and my 186 mL, really it is only a miniscule figure of 0.1 mole thereabouts. But nevertheless I will use the algebra to calculate.
[Edited on 20-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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|
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