Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
sodium cyanide : NaCN
hydrochloric acid : HCl
zinc : Zn
nitric acid : HNO3
rhenium : Re
Class:
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elem=Re
coordination
redox
Summary:
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Rhenium, when dissolved in nitric acid, gives colorless perrhenate ions,
[ReO4]-. With zinc, in the presence of hydrochloric acid of sufficient
concentration, this can be reduced to a yellow/green species. With cyanide,
in alkaline environment this forms a brown and clear solution. The yellow/
green species may be [ReCl6]2-, which according to literature is green.
With cyanide, a complex may be formed.
Description:
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Add a small amount of rhenium metal to a few drops of concentrated nitric
acid and heat a little: The metal quickly dissolves. The liquid becomes
green at first and later it becomes light yellow. The green color probably
is due to the presence of NO2/N2O3 in the concentrated nitric acid.
Add 1 ml of concentrated hydrochloric acid (30% HCl) to the liquid: The
resulting liquid is very light yellow, almost colorless.
Dilute the liquid with the same amount of distilled water: The liquid now
becomes really colorless.
Add a spatula of zinc: The zinc dissolves, the liquid becomes yellow/green
and a lot of hydrogen is evolved. The liquid becomes warm. Finally, when all
zinc is dissolved, the liquid is clear and yellow/green.
Dilute again with an equal volume of water and then take approximately 1/3th
of the volume of the now light yellow/green liquid. To this, add some solid
sodium cyanide: The sodium cyanide dissolves and the liquid becomes yellow
and turbid. The solid in the liquid is white, it probably is due to the
presence of Zn2+ ions in the liquid. After some time, the color has shifted
towards yellow/brown and the liquid is still turbid.
Add an excess amount of a solution of sodium hydroxide, such that the liquid
becomes fairly strongly basic: The liquid becomes clear and light brown. The
Zn2+ forms soluble zincate (II) in the strongly alkaline liquid and the
rhenium species now forms a brown compound. Is this a complex with cyanide?