Colors range from green yellow orange to red. How does the sugar concentration and Cu2O concentration cause this? I know Cu2O is red. Why is there a green or yellow color instead of just red or some kind of red?


Benedict's Reagent is just simply $\ce{Cu^2+}$ ions in the form of copper citrate. When Benedict's Reagent finds an aldose (a sugar with an aldehyde group), it can oxidize the aldose to a carboxylic acid. For example:

D-Glucose being oxidized

Since D-Glucose is oxidized, Cu is reduced to a red precipitate ($\ce{Cu2O}$). The colors range form green to red because the original Copper Citrate ($\ce{C6H8Cu2O7^4+}$) is blue in color.

Source: Quora

  • $\begingroup$ how does it become green if cu2o is red? $\endgroup$ – Soapkz Sep 15 '17 at 13:58
  • 1
    $\begingroup$ "The compound can appear either yellow or red, depending on the size of the particles." en.wikipedia.org/wiki/Copper(I)_oxide yellow + blue =... $\endgroup$ – Mithoron Sep 15 '17 at 14:21
  • $\begingroup$ How does that relate to concentration? And what about green? $\endgroup$ – Soapkz Sep 16 '17 at 11:37
  • $\begingroup$ Color theory - Yellow Copper(I) Oxide + Blue Copper Citrate = Green solution $\endgroup$ – JSCoder says Reinstate Monica Sep 16 '17 at 15:58
  • $\begingroup$ So at higher concentrations copper oxide particles clump together? $\endgroup$ – Soapkz Sep 17 '17 at 12:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.