CHRIS25
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iodometric titration confusion
Having spent a number of days studying this I am a little confused as follows:
1. Determine Copper ions in solution: Is the potassium Dichromate really necessary, to standardize the thiosulphate solution.I have never read this
anywhere else with regards to using the dichromate.
2. Determine Ferric ions in solution: I read this for reagents needed - -
Titrant: 1mol/L standard Na2S2O3 solution
Glacial acetic acid 50% w/v KI solution (store in amber bottle in a cool place).
0.04mol/L KIO3 solution (for standardizing Na2S2O3 titrant)
Th acetic I can understand (to ensure acidity I think to prevent hydrolysis); but then Potassium Iodate? All my reading has led me to believe that
the iodate is never used in Iodometry. Only the Iodide (which I have ordered especially), since it is iodide and the resultant iodine (I2 + I- = I3-
(Sorry I can not see where on earth I can make supoerscript and subscript) that is then put with the thiosulphate. So these extra ingredients are a
mystery.
[Edited on 29-4-2014 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)
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Bert
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Could you post where this information you're working from was found?
| Quote: |
Sorry I can not see where on earth I can make supoerscript and subscript)
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Hit the "post reply" button to bring up options such as sub, superscript. If you've started off in quick reply mode, hitting "preview post" will also
bring up these options.
Or just keep the code loaded in your clipboard for quick use while doing "quick reply".
It is more professional looking when you take the time to format equations properly- I do appreciate that little bit of extra precision.
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1. Attempt to re-express your target’s position so clearly, vividly and fairly that your target says: “Thanks, I wish I’d thought of putting it
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2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
Anatol Rapoport was a Russian-born American mathematical psychologist (1911-2007).
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CHRIS25
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thankyou, I see it, the two buttons with x and y.
The copper:http://www.nitm.ac.in/Documents/students/Expt%204.pdf
The Ferric: http://www.metrohm.com/com/Applications/methods.html?identif...
I also learned that Potassium Iodate is used Only with iodimetry, hence the confusion on this particular one.
Actually I think I will cancel the order. I thought it would be good practise and learning if I could learn how o determine copper and ferric ions in
solutions that I often do. I have read so much over these last day sand much of it involves buffer solutions, maintaining PH levels, adding
different chemicals to thiosulphate, depending on which doc I am reading. To be honest it is all over my head and then the stoichiometry I have not
even begun to figure this one. It all looked quite straightforward on paper, the ionic equations and the reducing and the whole process seemed so
easy to follow, but that was theory. So I think I have pushed myself one step too far on this one just to be plainly honest.
[Edited on 29-4-2014 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)
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blogfast25
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I would not recommend either of these titrations if you have little experience with titration in general. Start with some simple acid base titrations,
or may be a very simple iodometric one. Once you've done these, you'll understand better how the more advanced ones are supposed to work.
Stoichiometry is usually embedded in the formula to calculate your results and that formula is usually provided with the method. For the Metrohm
procedure that's on page 2.
It's often been said the sodium thiosulphate of good quality can be used without standardising, which saves a bit of time without sacrificing much
accuracy.
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CHRIS25
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Hi blogfast, I have done quite a few basic titrations: Determining free Cl- in copper chloride, Molarity of various acids, I am sure others
as well, and am familiar with quite some stoichiometry, and never stop learning new stuff. So I should be able to do this....
To put it in a nutshell, (I have lab grade Sodium thiosulphate by the way), in a nutshell therefore I was under the impression that one simply adds
excess Potassium Iodide to the analyte, The KI is reduced by the analyte to Iodine. This is then titrated with Thiosulphate until (Starch turns
blue-black in the presence of iodine. Therefore, when the blue-black color disappears, the iodine has been completely reduced to the iodide ion.) as a
direct result of starch indicator, the amount titrated is the measure of chloride or ferric in the analyte. This is my very basic understanding.
1. I do not understand how one is to know when one gets "Near the endpoint" before adding the starch indicator, I have been unable to find a single
video about this.
2. On page 2 from the PDF, what does "Titre" mean? and what is "Blank" supposed to mean? And the sample volume is, I imagine, the amount of analyte
used for the analysis?
3. Is what I have written about my basic understanding all that is required as far as reagents are concerned?
Unfortunately not being able to see demonstrations I am trying to build a mental picture of the whole situation, just so that I can at least begin
with copper and ferric ions. If this is successful then then I have something to build upon.
[Edited on 29-4-2014 by CHRIS25]
[Edited on 29-4-2014 by CHRIS25]
[Edited on 29-4-2014 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)
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blogfast25
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I think your understanding is probably just about enough.
In the case of Fe3+, it oxidises iodide to iodine:
Fe<sup>3+</sup> + I<sup>-</sup> === > Fe<sup>2+</sup> + ½ I<sub>2</sub>
This colours the solution reddish. As you start titrating that colour gradually fades because the iodine reacts away with the thiosulphate. Near the
end point it is slightly yellow from the remaining iodine. Then you add the starch, which will make it blue. Titrate further till the blue has faded
to colourless. That’s your end point.
A ‘blank’ means titrating distilled water in the same conditions: it will give you a very, very small burette reading, sometimes 0.
The ‘titre’ of a titrant solution represents the actual concentration of titrating reagent. If you prepare a solution of say 0.05 N Na2S2O3, it
will never be EXACTLY 0.05 N. The exact concentration is obtained by multiplying the nominal concentration of 0.05 N with the titre t. The titre t is
either found through standardisation or from the weight used to prepare the Na2S2O3 solution. You will need a volumetric, calibrated flask to prepare
such a solution. A titre of say 0.9957 would means the actual, precise concentration is 0.05 N x 0.9957 = 0.04979 N.
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aga
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| Quote: | | I can not see where on earth I can make supoerscript and subscript |
It's like this, but the stuff in the square brackets needs to be all on one line.
[
sub
]
subscript
[
/sub
]
Superscript is 'sup' instead of 'sub'.
example :-
sub and super
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CHRIS25
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Ok blogfast this is completely clear now. So for my purposes I can ignore 'blank'. And the titre is also not necessary since lab methodical accuracy
is not my intention, nor can it be in a kitchen where I employ the use of a syringe and needle with 0.1mL increments to do all my titrations (burette
and stuff is very expensive). But a good enough accuracy for me can certainly be obtained. Besides it is the learning that is important.
So what I am looking at is this:
Fe3+ g/L = (amount of Na2S2O3 titrated) x 56g/mol / vol of CuCl or ferric/ferrous chloride analyte
I keep reading about solutions "that are too acidic", and this always seems to be a subjective comment as opposed to some methodical calculation. It
bothers me since by their nature copper chloride and ferric chloride solutions are,well, extremely acidic. Can you please clarify on this point, is
it really a recipe for a very inaccurate titration as seems to be suggested?
‘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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aga
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Er ...
"A titre of say 0.9957 would means the actual, precise concentration is 0.05 N x 0.9957 = 0.04979 N"
What's an 'N' ?
I've broken my first Burette doing titrations using Molar concentrations, and now an 'N' appears, and also a 'Titer'.
Have i done ALL my titrations fundamentally wrong using a known molarity titrator ?
[Edited on 29-4-2014 by aga]
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gdflp
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N stands for normality. For example in a 1M solution of HCl, both H+ and Cl- ions are 1N, however in 1M H2SO4, the H+ concentration is 2N while the
SO4 concentration is 1N still.
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aga
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Oh great.
So now we're varying Normality.
Thanks for the clarification.
Am i right in guessing that Normality is the Ionic concentration/ratio depending on the Molarity and the compound's Ionic composition (in solution) ?
E.g. a 0.1M solution of NaOH would be 0.1N as well, seeing as there's just Na and OH in ions there ?
Also, a 'Titer' of 1.002 would means that those numbers are bollocks, by a factor of 1.002 ?
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gdflp
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For the NaOH yes, for the titer, sort of see this page. Generally acids are listed by the normality of their H+ ions, and bases for their OH- ions. eg .001M Ca(OH)2 is .002N and 1M H3PO4 is
3N.
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aga
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Wow !
I get it.
Many thanks gdflp.
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blogfast25
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For multiprotic acids, multiply molarity by n (number of protons) to get normality.
In redox titration (like the one being discussed), multiply M by the number of electrons a species absorbs (reduction) or loses (oxidation).
In titrations, normality is used instead of molarity, it makes things a little easier. In some case N = M, e.g. NaOH and HCl.
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