General comments about HI reductions
Addition of a reactant that will react with HI to get the I from HI and release H2O will considerably drop the concentration and might bring it to a level which is too low to be useful to continue the rxn and this will block everything.
To avoid this happening, using more HI solution is a good way to go. But adding more I2 will also bring the concentration higher if enough RP is present. If 2nd route is choosen the rxn will release HI gas as it proceeds (reduces the substrate)
This can be explained as follows:
The substrate will use I2 (from HI),release H2O, you will add some more I2 to bring the conc. of the acid back to %57 and when the substrate gives its iodine back to be reduced the rp will convert the given I to HI which will be excess and escape from the condenser as the rxn proceeds. This might be a good sign of a complete rxn. When fuming stops the reducing
is complete (30-48 hours)
Also using freebase reactants will considerably push the yields up because the HCl ions will harden the formation of HI due to the Cl- ion which is a better nuclepohile than I-
Now lets get to the calculations:
T: Amount of H2O put at the start
L: Amount of H2o left from the HI synthesis
U: Amount of H2o used for the HI synthesis
T=L+U
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G: Amount of HI dissolved (in the leftover H2O(L))
S: Amount of the total solution
(1) S=G+L
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For a max %57 solution
(2) (S.57)/100=G (The amount of dissolved HI is equal to the %57 of the final solution)
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In the above equation put (G+L) in the place of S (S=G+L)
(3) ((L+G).57)/100=G
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To find U we can use the following equation
3H2O + PI3 -> 3HI + H3PO3
This means that: For every mole of HI synthesised we waste 1 mole of H2O (1:1)
U= Nu . MwH2O (Nu: Mole amount of wasted H2O , MwH2O: Molecular wt of h2O=18)
Nu=Ng (Ng: Mole amount of synththesised HI)
(4) U=Ng.18
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T=L+U =>
L=T-U
==acc to 4=>
(5) L=(T-(Ng.18))
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To find G (Amount of HI in the sol.)
G= Ng . MwHI =>
(6) G=(Ng . 128)
NOW TO (3) PUT
G AS (6)
L AS (5)
|----L----||---G----| |---G----|
( ((T-(Ng.18))+(Ng.128)) .57) /100 = (Ng . 128)
(T+110Ng)57=12800Ng
When you solve the eqation the result will be
(7) T = 114 . Ng
So what does this mean?
this means that the amount of water that will be put in the reaction from the start
should be 114 times of the mole amount of the HI that will be synthesised
Or this can be tweaked as
Ng = Mg / MwHI
Ng= Mg / 128
If you put the above value in the place of Ng at (7)
and solve the equation
(
T= 0,89 . Mg
Mg means the weight of HI in the reaction mixture.
Because we use 1 mole of Iodine for every mole of HI created the results will be identical.
AND THE FINAL RESULT IS
T= 0,89 . Mg
THIS MEANS THAT WE SHOULD START WITH H2O WEIGHING 0,89 TÝMES OF THE I2 ADDED.
(T IS H2O ADDED AT THE START - Mg ÝS THE WEÝGHT OF HI WHÝCH IS TAKEN EQUAL TO I2)
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In other words the GOLDEN EQUATION is:
A: The weight of the water put in from the start
B: The amount of I2 that should be added
A= 0,89 x B
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Example
For 10mls H2O
10=0,89.B
B=11,2
11,2 g I2 should be added
And the result will be 21,2 gms of %57 HI solution
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These are golden equations that will help anyone interested in HI/RP reactions. All this hard work will be best rewarded only if it helps some bee here.
Thanx