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Copper(II)-iron(II) sulfate

From Crystal growing


   Copper(II)-iron(II) sulfate   
Names: copper(II)-iron(II) sulfate
copper-iron sulfate
Formula: (Cu,Fe)SO4 (anhydrous)
(Cu,Fe)SO4 · 5H2O (pentahydrate)
(Cu,Fe)SO4 · 7H2O (heptahydrate)
Molar mass: 155.757 g/mol (anhydrous)
245.831 g/mol (pentahydrate)
281.861 g/mol (heptahydrate)
Shapes:
https://en.crystalls.info/w/uploads/media/4/48/Prolongated_rhombic_prism.json
https://en.crystalls.info/w/uploads/media/6/67/Oblique_parallelepiped.json
https://en.crystalls.info/w/uploads/media/b/bc/Rhombic_prism.json
https://en.crystalls.info/w/uploads/media/d/d0/Truncated_deformed_oblique_hexagonal_prism.json
https://en.crystalls.info/w/uploads/media/a/af/Tetragonal_prism.json

Color: turquoise
sky blue
Stability: quickly erodes (hydrates)

Description

Co-crystal of copper(II) sulfate and iron(II) sulfate. From water solutions crystallizes as heptahydrate and pentahydrate.

Minerals

Occurs in nature as melanterite mineral.

Precursors

Mixing copper(II) and iron(II) sulfates

Chemical equation:

CuSO4 + FeSO4 = 2(Cu,Fe)SO4


For preparation of 100.00g of copper(II)-iron(II) sulfate heptahydrate а 44.29g of copper(II) sulfate pentahydrate and 49.32g of iron(II) sulfate heptahydrate is required.

Dissolve compounds in hot water apart and then mix solutions into one container with intense stirring. Cooling or evaporation of a solution will cause double salt crystallyzation.

Reaction between copper(II) sulfate and metal iron

Chemical equation:

2CuSO4 + Fe = (Cu,Fe)SO4 + Cu↓


For preparation of 100.00g of copper(II)-iron(II) sulfate heptahydrate а 177.17g of copper(II) sulfate pentahydrate and 9.91g of iron is required.

Add copper(II) sulfate solution to the flask, then add iron pieces, shavings or powder and leave for a few days. After solution color changing will stop, less active metal will completely displace into the precipitate. Then filter the solution.

Influence of impurities

Addition of large amount of sulfuric acid produces crystal hydrates which are more stable in the open air. Even small addition is helpful because it prevents forming of orange iron(III) hydroxide precipitate.
Color of final crystals and their shape depends on the ratio between sulfates in the mixture - more iron(II) sulfate makes crystals green, more copper(II) sulfate makes crystals blue.
Increasing iron(II) sulfate concentration makes crystals more stable in the open air. Crystals with iron:copper=1:1-2:1 ratio dehydrates just in minutes, but 3.5:1-4:1 ratio dehydrates within several hours or even days. Dehydration starts from large defects on crystal surface, then other surface is affected.

Notes

These crystals are the result of isodimorphism, they are formed only from solution containing both sulfates. If crystals are dissolved and crystallized again, ten crystals of each sulfate will grow separately.

Storage conditions

For crystal storing use hermetic vessel with small amount of saturated solution at the bottom or place wadding moistened with such solution. You can use such alternatives as vessel with vaseline or vegetable oil, organic non-hygroscopic solvent (kerosene, benzine or paraffin). Also you can use acrylate polymer or another kinds of solidifying plastic.


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