July 21, 2010, from
Lloyd Erlick,
here is what I found in my notes regarding the manufacture of potassium
sulfite in the darkroom. It came from a kindly chemist. (Sorry for funny
typeface ...)
Making potassium sulfite:
Potassium Metabisulfite
[K2S2O5]
is dirt cheap, add some Potassium Hydroxide [KOH] and you have liquid
Potassium Sulfite
[K2SO3].
K2S2O5
+ 2(KOH) -->
2(K2SO3)
+ H2O
222 g 112 g 316 g
------------------------------------------------
(minutely less than?)
2 parts metabisulfite + 1 part KOH 3 parts K sulfite
18 grams 9 grams 27 grams (approximate)
17.5
g
9
g
25.2 g (closer to exact)
_____________________________________________________________________
July 28, 2006:
Figuring out the weights of chemicals involved in the above
equation?
Atomic weight of each component element:
K 39.1
S 32.1
O 16
H 1
Therefore:
K2S2O5
+
2(KOH)
-->
2(K2SO3)
+
H2O
K2 ?
78.2 2K ? 2(39.1) =
78.2
2(K2) ? 2(78.2) =
156.4
H2 ? 2
S2 ?
64.2 2O ? 2(16) =
32 2S
?
64.2 O ? 16
O5 ?
80 2H ? 2(1) =
2
2(O3) ?
2(48) = 96
_________ ____________________
________________________ _______
222.4
112.2
316.6
18.0
222.4 + 112.2 =
334.6
316.6 + 18.0 = 334.6
Notes:
The total weight of both reagents and reaction products is 334.6.
Reagents (Inputs)
?Potassium Metabisulfite represents (222.4 / 334.6) x 100 = 66%
(two-thirds).
?Potassium Hydroxide
is
(112.2 / 334.6) x 100 = 33% (one-third).
Reaction Products (Outputs)
?Potassium Sulfite is (316.6 / 334.6) x 100 = 94.6% (call it
95%).
?Water
is
(18.0 / 334.6 x 100 = close enough to 5%.
Therefore:
The weight of Potassium Sulfite produced by the reaction amounts to
95% of the total weight of Potassium Metabisulfite and Potassium
Hydroxide.
Note: when preparing the input reagents, be sure that the weight of
Potassium Metabisulfite is twice that of Potassium Hydroxide, less about
one percent.
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