Sciencemadness Discussion Board - KBr.CuBr2 double salt aka KCuBr3


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Fery

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Posts: 1015
Registered: 27-8-2019
Location: Czechoslovakia
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posted on 7-2-2020 at 08:09

KBr.CuBr2 double salt aka KCuBr3

I found this info about 1 year ago:
http://copper.atomistry.com/cupric_bromide.html

Quote:

double salts are exemplified by the black 2LiBr,CuBr2,6H2O; KBr,CuBr2, lustrous, dark-coloured prisms; and the green 2NH4Br,CuBr2,2H2O

From the 3 possibilities I chose the KBr variant because it is anhydrous (stability) and surprisingly in 1:1 ratio - others are 2:1 and also Cu2+ is known to form [CuBr4]2-

Reagents:
48% HBr, CuO (prepared by myself from CuSO4 + 2 KOH -> Cu(OH)2 and then Cu(OH)2 -> CuO + H2O), KBr, conc. H2SO4 (as desiccant).

Glass:
2 beakers (25 ml), 700 ml glass jar (from pickles, honey etc) suitable for containing both beakers inside.

Procedure:
Put 5,01 g 48% HBr into 25 ml beaker and add 1,30 g CuO in small portions (in excess as I prepared it by myself so it was far from 100% purity), slightly warm, and at the end short mild boil to expel traces of Br2 (HBr used was just right from the bottle, not freshly distilled). Filter out small unreacted excess of CuO and wash the filter with H2O.
Add 3,68 g KBr into the beaker and dissolve it.
Let it to evaporate at room temperature for 1 week.
Put the beaker into a jar. Put 10 ml of conc. H2SO4 into another 25 ml beaker and insert the beaker into the jar and close the jar lid tightly.
After 10 days no visibility of crystals but the volume of Cu solution with slightly smaller volume. Remove the formerly 10 ml H2SO4 (now diluted and with little expanded volume) and replace with 15 ml of fresh conc. H2SO4.
After 1 week not yet signs of crystallization, volume of thick Cu solution in beaker about 5 ml, but after 2 weeks the salt climbing up the beaker walls finally, after 3 weeks completely dry crystals without any H2O.
I chose jar and 2 beakers method instead of desiccator to prevent rapid drying. The slower the process the bigger crystals (the surface of H2SO4 in 25 ml beaker is much smaller than in desiccator).

photos will follow soon...

all materials concerning the product in the attachment

Attachment: CorrigeChimieEquilibre-6.pdf (821kB)
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Attachment: holmes1975.pdf (387kB)
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Attachment: inoue1967.pdf (363kB)
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Attachment: stepakova2007.pdf (330kB)
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