Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
acetic acid : CH3COOH
niobium pentachloride : NbCl5
Class:
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elem=C,Cl,Nb
acid/base
precipitation
Summary:
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Niobium pentachloride reacts with acetic acid, giving a colorless fuming gas
(most likely HCl) and a fuming liquid (most likely acetyl chloride).
Description:
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Add some solid NbCl5 to a small amount of glacial acetic acid: The solid
partially dissolves and the liquid becomes yellow. The remaining solid remains
at the bottom as bright glass-like yellow pieces.
Carefully heat the liquid a little bit (hot to the skin, but not unbearable,
probably 50 C or so): The liquid starts bubbling/foaming and the yellow color
disappears. The yellow solid only slowly dissolves in the liquid. A white fume
can be observed, which leaves the test tube. This white fume is due to the
presence of HCl. Finally, all of the solid dissolves and the liquid becomes
colorless.
The liquid is strongly fuming in contact with air.
Expected reaction: 2CH3COOH + 2NbCl5 --> 2CH3COCl + 2HCl + 2NbOCl3
Pour the resulting fuming liquid in some water: At once, a white solid is
formed in the water, which loosely sticks to the glass. This white solid most
likely is hydrous niobium pentoxide.
Decant the liquid from the white solid and add conc. HCl (30%) to the solid:
The solid does not dissolve.