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SnailsAttack
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Quote: Originally posted by Tsjerk  | | My god, just use molarity. I have worked in labs for years, never ever have I doubted grams not being per volume. |
Like I said though, the internet suggests that solubility is usually measured per unit solvent.
Molality has its advantages, namely being that I don't have to bother with volume measurements.
| Quote: Originally posted by Tsjerk | | Saturated solutions you have on hand by having a bottle with a thick layer of solid on the bottom of the bottle, and even then; who cares how much is
actually dissolved. |
You're thinking too inside the box. Yes, for most lab purposes you can just take the solubility of 320 g/L at 20°C given by wikipedia, but depending
on what source you look at, the solubility of the pentahydrate ranges anywhere from 208 to 360 grams per liter at room temperature. That level of
ambiguity isn't good enough, I want to get this stuff figured out so I can start to look at other unsolved problems.
I'm also interested in reliable solubility values for use in geochemistry (e.g. ocean salinity) and purifying salts by solvent extraction and
fractional dissolution/recrystallization.
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SnailsAttack
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Solubility of CuSO₄·0H₂O and CuSO₄·5H₂O in grams per kilogram of water | Code: | 0°C 138.5 235.0
10°C 170.8 295.7
20°C 207.8 368.3
30°C 247.4 449.8
40°C 291.9 546.7
50°C 341.6 662.0
60°C 399.7 807.4
70°C 466.4 990.3
80°C 543.2 1225
90°C 637.2 1557
100°C 751.0 2039
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I converted the graph to a table from the paper that Yob posted. The paper's based on an extensive meta-analysis, so I trust it pretty well.
Each value is accurate to probably ± 1.7%. The solubility values for the pentahydrate are calculated from the anhydrate using the formula I came up with in the original post.
I think it's worth mentioning that the mean solubility I measured earlier is accurate to an astounding 0.25% with respect to this table, which might suggest that the error range is lower
than what I proposed.
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yobbo II
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From Kirk Othmer:
The pentahydrate slowly effloresces in low humidity or above 30.6C. Above
88C dehydration occurs rapidly.
Anhydrous copper(II) sulfate [7758-98-7] is a gray to white rhombic crystal
and occurs in nature as the mineral hydrocyanite. CuSO 4 is hygroscopic. It is
produced by careful dehydration of the pentahydrate at 250C.
Yob
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SnailsAttack
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I found a pdf copy of a book on solubility that might be valuable:
https://ia904709.us.archive.org/12/items/2ndsolubilitieso00s...
It was published in 1907 and includes data from as far back as the mid 1800s, which is how you know you're in some s***.
There's solubility data for copper sulphate at the bottom of page 300, and the error with respect to the table I posted above ranges from 3.2% to as low as 0.4%, which suggests that it's most likely reliable unless there's some circular
referencing going on.
The book actually makes the distinction between solubility as measured by 'unit per unit solution' compared to 'unit per unit solvent', which, if this
thread has taught me anything, is extremely important.
In the book's foreword, the author reaches pretty much all the same conclusions as I have:
| Quote: | | In those cases ... where the amount of solvent is expressed in volume instead of weight, it is first necessary to multiply by the specific gravity of
the solvent in order to find the weight corresponding to the given volume. |
| Quote: | | One of the forms of presenting solubility data for which especial care is needed in converting the values to a different basis is in the case of
results for salts with water of crystallization. |
| Quote: | | ...if, for instance, the grams of hydrated salt per 100 grams of saturated solution or of water have been given, then it will be necessary to add the
weight of water present as water of crystallization in the salt, to the weight of water present as solvent. The total weight of solvent is, therefore,
made up of the weight of water used for preparing the solution and that carried by the salt as that of crystallization. |
More testing is needed to verify that the theories and formulas I've written in this thread actually work, but at the moment I'd say things are
looking pretty good (aside from the fact that I'm falling back to the findings of a textbook written 20 years before the invention of sliced bread)
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Texium
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Everything you’ve quoted is stuff we all already know and fully agreed about, so I’m having a little trouble seeing what new insight you got out
of it.
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SnailsAttack
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| Quote: Originally posted by Texium | | Everything you’ve quoted is stuff we all already know and fully agreed about, so I’m having a little trouble seeing what new insight you got out
of it. |
it's some confirmation, plus a source of potentially reliable data on the solubility of a whole buttload of salts
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