Reduction of Fehling's solution

A movie depicting a reduction of Fehling's solution (a complex of copper II sulfate in alkaline sodium potassium tartrate solution) by glucose to form a precipitate of copper I oxide. Glucose is oxidized to gluconic acid. This reaction is used as a test for aliphatic aldehydes (e.g., formaldehyde, acetaldehde) and monosaccharides, e.g., glucose (which also contains aldehyde groups).

Category:

Science & Technology

Tags:

• Fehling's
• solution
• glucose
• aldehyde
• copper
• oxide

[Ortilochus]

I did the same experiment but with acetaldehyde(ethanal)and the solution went green then to a yellow/brown precipitate. Anyone know why!

[evansp12]

It may be that there wasn't enough acetaldehyde added and so the reaction is incomplete. The final product should be orange brown, so you're almost there.

Another possibility is that acetaldehyde may polymerize to a resinous product if there is excess of sodium hydroxide in Fehling's solution.

Anyone who has better answers please comment, thanks.

[MariusSemeonOrtiz]

Good video and description, 5 starts!

Was acctually just studying 3 tests for aldehydes a week ago for chemistry exam:

1. Potassium Dichromate turns orange to green,

2. Fehling's Solution turns blood red,

3. Tollens Reagent (ammonical AgNO3) form's a ''silver mirror'' of precipitated silver.

[MultiBeenish]

nice taught alot

[idiotkrati]

yeh it is !

[trarthas91]

is this like benedict's solution?

[idiotkrati]

Did you have Cu2+(aq) in the solution ? And you god it redusated by using flame, so it became Cu2O ?

Where on the aldehyde is the Cu2+ ?

Thank you so much for the video.

[slateflash]

I agree with evansp, bt it may be hydrated copper(I) oxide.

[Ortilochus]

Thanks for for the explanation.