CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Is this stoichiometry correct please
I would like to make sure that I am understanding things absolutely correctly. Thankyou.
To determine mass percent and molarity of solution of FeCl2:
Fe Content in original solution = 29g
FeCl2 tetrahydrate 199g/mol
weight of whole solution + crystalline mass so far = 91.8g
Mass% = 29/91.8 x 100 = 31.6% FeCl2
Molarity of solution = (31.6%/1) x (1/199g/mol) x (1/100) x (1.39 SG/1) x (1000/1) = 43924/19900 = 2.2M FeCl2
Max possible molarity of a FeCl2 soln = 1000/199g/mol x 1.39 SG = 6.98M
Thankyou for checking, this forum is my only reference for making sure that I learn correctly.
[Edited on 20-4-2014 by CHRIS25] sorry I tried to delete this post and put into short questions thread but can not see how to delete.
[Edited on 20-4-2014 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)
|
|
|
Bert
|
Thread Moved
20-4-2014 at 09:09 |
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
This depends on what 'Fe Content in original solution" means.
If it was tetrahydrate crystals, then the FeCl2 content was 87.5% of 29g = 25.37g, as the rest was the hydrate(water).
That would mean that in 91.8g the % w/w of FeCl2 would be 27.6 %
FeCl2 is 126.7g/mol so you would use that instead of the tetrahydrate mass of 199g/mol.
I am an absolute beginner, so don't take my word as being gospel.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Well thanks for responding though, it was elemental Iron filings in HCl. And the reaction is completed apart from Oxidation of FeCl2 to FeCl3, but
that does not matter. So the measurements are based upon a FeCl2 solution with some precipitating out. I was not sure about whether to use the g/mol
of the tetrahydrate or the anhydrous, I used the former calculation since that it what I will be ending up with plus I imagined that really even with
the anhydrous it will make no difference since there the weight of the end solution is still what I actually have in total right now.
[Edited on 20-4-2014 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)
|
|
|
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
I think FeCl2 will disassociate into Fe+ and Cl- in a water solution, so it'd be the anhydrous weight.
Without any data about the original reactions, it's impossible to work anything out.
How many grammes of iron filing, what volume/weight/molarity of HCl ?
Does this mixture make the 'Fe Content in original solution = 29g' you mentioned ?
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by CHRIS25  | To determine mass percent and molarity of solution of FeCl2:
Fe Content in original solution = 29g
FeCl2 tetrahydrate 199g/mol
weight of whole solution + crystalline mass so far = 91.8g
|
By summarising this so extremely you make it hard for us to help you. We need to understand what your purpose is, what you created and how.
I haven't checked your musings but they seem unnecessarily complicated.
To calculate the molarity of an FeCl<sub>2</sub> solution, all you need to know is the amount of Fe in solution and the total volume of
that solution.
You have 29 g Fe in solution, that is 29 g / 55.845 g/mol = 0.52 mol Fe. Divide this by the volume (in litre) of the solution and that gives you the
molarity (mol L<sup>-1</sup> or more scientifically mol dm<sup>-3</sup> of Fe or FeCl<sub>2</sub> in that solution.
For 'maximum possible molarity', for instance based on solubility data, you must always use the anhydrous form of the substance, unless explicitly
stated otherwise. Most Wiki solubility data are based on anhydrous substances, as the hydrates only exist as crystals, and not as solutions.
[Edited on 20-4-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
I do not understand why the following data is necessary? I presumed that, within the context of this operation only, how I started is redundant
information, what is important is how I ended? The only losses being oxygen and Hydrogen and chlorine. Anyway here it is:
Fe+2HCl = FeCl2+H2
Using Iron filings and 11.6HCl at 1.18 SG
29gFe + 125mLs 11.6M HCl + 100mLs H2O
0.5 mole + 1 mole (86mLs) with extra HCl to prevent hydrolysis of Fe to its hydroxide
Simmered down
Filtered
Another 40mLs 6M HCl added
simmered down and partially oxidized
Very bright green crystals obtained in remaining solution which is now exactly 70mLs and is a mix of FeCl2 and FeCl3
Total weight of solution = 91.8g (Density of solution will not change even with dissolving so the 70mLs still holds true)
‘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)
|
|
|
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
Given that the Fe governs how much FeCL2 is formed,
and you used 29g (0.519 moles) of Fe then you can have a
maximum of that many moles of the product.
So 0.519 moles in 70ml = 7.42M
If it is hydrate then it would be 199.8 x 0.519 = 103.7g in 91.8g = 113% w/w
so i guess it is not hydrate, 126.75 x 0.519 = 65.7g in 91.8g = 71.7% w/w
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
This all began because of a comment I read in the eventual production of magnetite (Fe3O4). Quote: the amount of iron used and total weight of
solution will tell you the concentration of the FeCl3 you have. Now I know that I have made 0.5moles of FeCl2, but there will be slight loss during
the production from the raw state to the final FeCl3, via precipitation, filtering, discarding of residues on filter paper, it may contain 0.5moles in
20mLs or 100mLs but, big but, if I need to add 5mLs of FeCl3 to something I have to know its concentration, 10mLs of my product will be different
concentration than 15mLs. So I need to know that concentration. So I reasoned out , obviously completely cock-eyed, get the mass %, convert that to
Molarity, find out max possible molarity that this solution can have. But it appears I am wrong again and so am all confused now.
‘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)
|
|
|
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
No : The 'concentration' will be the same.
The number of molecules in 10ml or 15ml will be different, but the Molarity or Concentration remains the same.
Basically you have (a maximum of) 0.5 x 6.022 x 10^23 molecules of product in the 70ml of solution.
If you take 10ml of solution, it will have 10/70 of that number of molecules in it, but the [M] would still be 0.5M.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
I understand that taking whatever amount from the solution does not change Molarity but you withdraw less moles of product. I am just confusing
myself because I am taking the amount of Iron in solution (that I know dissolved) and taking the final weight of the 70mLs of solution and getting a
big rubbishy calculating nightmare. Please can I start again. I know that this FeCl3 is approximately 0.5mole, weighs 92grams and is 70mLs.
0.5moles/0.07 L = 0.7Molarity. Right so to calculate the concentration via taking 92grams weight of solution as it now stands and 29grams of
elemental iron how is this done since my method in original post was wrong?
‘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)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
C25:
You are indeed confusing yourself.
Your purpose is to make a solution of FeCl3, of known concentration (molarity).
To achieve this you dissolved 0.5 mol of Fe as FeCl2. Now you want to convert your FeCl2 to FeCl3 by whatever means. Well, whatever you do and
assuming there are no losses of FeCl2 or FeCl3 along the way, you ALWAYS have 0.5 mol of product. Divide this by the final volume of the solution and
assuming all product stays in solution, then that number (0.5 mol / final volume in L) is your molarity.
It's pointless to work with 'weight of solution', unless you know the density of the solution, so you can convert the weight back to volume (= weight
/ density).
The easiest way to produce such a solution is to dissolve the iron in a considerable excess of HCl, then cool that solution on ice and slowly oxidise
it with ice cold H2O2, stirring very vigorously and cooling along the way. Then gently simmer for a bit to remove any excess H2O2 and note final
volume. Use stoichiometry to calculate how much H2O2 solution you will need.
[Edited on 21-4-2014 by blogfast25]
| Quote: Originally posted by CHRIS25 | | Right so to calculate the concentration via taking 92grams weight of solution as it now stands and 29grams of elemental iron how is this done since my
method in original post was wrong? |
You just DON'T DO IT that way. Get it out of your head: it is WRONG. 
[Edited on 21-4-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
It seems so, pickling myself in a solution of stoichiometric acid!
One Last question, I understood by reading something, that to discover the maximum possible molarity of that any product can achieve one calculated as
follows:
1000mLs/molar mass x S.G
is this correct?
[Edited on 21-4-2014 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)
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
