# What is the optimal wavelength in a spectophotometer for copper 2+ ions?I am trying to find the amount of glucose in a juice. By reacting it with excess Fehling's solution, I will have copper 2+...

What is the optimal wavelength in a spectophotometer for copper 2+ ions?

I am trying to find the amount of glucose in a juice. By reacting it with excess Fehling's solution, I will have copper 2+ ions left over. Now I want to quantify it. My teacher said I could do it using the spectrophotometer but need to find the optimal wavelength. Do any of you know? Thank you.

*print*Print*list*Cite

### 1 Answer

The instrument has to be set at 400-800 nm. The optimal wavelength, however has to be set at 465 nm. Fehling's solution A is a blue aqueous solution of copper sulfate, while Fehling's B is a clear solution of aqueous sodium potassium tartrate and alkali. Both react to form a blue colored chelate complex of Cu2+. It reacts with reducing sugars like glucose to give red precipitate of Cu2O. By reacting glucose with excess Fehling's solution, and estimating copper 2+ ions left over through colorimetric estimation is a practical option. But it is unreliable at the same time as the complex is highly sensitive to light. So the process has to be completed fast.