[Atome]

Hello everyone,

I cannot think of a logical answer to the following post-laboratory question. FYI, we conducted the Fehling's and Tollen's Tests to differentiate between ketones and aldehydes.

Thank you very much for your help.

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1. Notice that glucose was not reacted with the Tollen's solution (It was with only Fehling's). Do you expect a positive test in this case? Why do you think that this test was not carried out?

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My Work:

The molecular formula for glucose is C₆H₁₂O₆. From this info, I determined that C's oxidation number is 0  Carbon can undergo further oxidation or reduction.

Therefore, glucose would be a positive test for Tollen's solution.

However, I do not understand why this test was not carried out? If it was done for Fehling's test, it surely would not be more expensive or dangerous?

[macman104]

What does Fehling's Test give a postive result for?
What does Tollen's Test give a positive result for?

What functional group is present in glucose?

[Atome]

What does Fehling's Test give a positive result for?


What does Tollen's Test give a positive result for?

These tests are both for differentiating aldehydes from ketones. The Fehling's test involves a pale blue solution  brick red precipitate. The Tollen's test involves the formation of Ag_s.

What functional group is present in glucose?

I see mostly hydroxyl groups and one aldehyde group at the end of the chain. If this is correct, shouldn't Tollen's Test work as well and be performed as part of the lab?

[macman104]

Actually....um...yea, you're right, I'm not sure what I was thinking.  I don't have a good answer for you.