Ok, so you agree with my figures for the most part, the difference between my 44.5% and your 47% being the result of the simplification I used in the calculation, that is, disregarding the hydrogen in HI and just calculating from the weight of the iodine only.
So, what you are saying, then, is that the Vogel method uses the strategy of first getting a good rough acid strength approximation first, as in your example, say 47%, and then relies upon a distillation to get the final concentration.
In other words, the initial H2S preparation is intentionally less that the desired end product, relying upon a separate process, azeotropic distillation in this case, to arrive at the final concentration. OK, I see that.
Now, the question naturally arises, is this two step process, as opposed to the single step process, with its attendant added difficulties and glassware requirement, of any demonstrable benefit if the HI is not being used for analytical purposes?
That is, yes, of course, the two step process will give a purer product, a result necessary if the HI is to be used in quantitative analysis, but is that extra purity and precise control of concentration of any demonstrable benefit when the acid is to be used in a reduction reaction, especially when the recycling phosphorus is coming from matchbooks?
My point is this: HI by the sulfide reaction affords the average user a quick, cheap, and unlimited access to strong HI and reduces the phosphorus requirement by 75%
But that advantage to the average user vanishes if he is constrained to do a complex distillation with equipment that he likely does not have. In other words, it appears to be an unnecessary and artificial roadblock to what should be seen, otherwise, as a holy grail route to the acid.
In other words, it seems much like the pointlessness that I am guilty of above, that is, using a calculation simplification that introduces a 2% error and then reporting my result to two decimal places, silliness that is a result of pure habit.
An additional minor point, if distillation is performed, any remaining H2 S is lost, dissolved H2S in the acid will actually reduce further the phosphorus need in the main reductive reaction, a minor point though.
Can anyone tell me how to work all of those buttons and choices on the posting page, any instructions around?
NMR