TOLLEN’S TEST (Aldehyde Group)

Question

1. In a clean test tube, add 1-2 mL of the unknown organic solution
2. Then add 1-2 mL of the Tollen’s reagent and observe if there are any changes.
3. Using a test tube holder, hold the test tube containing the mixture in water bath for 1-2 minutes.
4. Observe any physical changes occurring and take note.

What is the possible results?

Answer 1

Tollen's test is a classic qualitative test used to detect the presence of aldehyde groups in organic compounds. Here are the possible results you might observe:

1. Positive Result:

   • If the unknown organic solution contains an aldehyde group, you will observe the formation of a silver mirror on the inner walls of the test tube after heating in the water bath. This occurs because the aldehyde reduces the silver ions in Tollen's reagent (which contains silver nitrate) to metallic silver, resulting in a shiny silver deposit.

2. Negative Result:

   • If your unknown organic solution does not contain an aldehyde group (and contains a ketone or is an alcohol instead), you will not see any change in the test tube. The Tollen’s reagent will remain colorless, and no silver mirror will form.

It is important to note that certain reducing sugars and some compounds containing particular structures can also give a positive result in Tollen's test, so the test is not solely specific to aldehydes. Always confirm results with further analysis if needed.