Functional Group Lab

Distinguishing Aldehydes & Ketones

Tests: Tollen’s Reagent & Fehling’s Solution
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Lab Manual: Theory & Procedure
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Principles

Tollen’s Test: Aldehydes reduce $[Ag(NH_3)_2]^+$ to metallic silver ($Ag^0$), forming a mirror. $R\text{-}CHO + 2[Ag(NH_3)_2]^+ + 3OH^- \rightarrow R\text{-}COO^- + 2Ag \downarrow + ...$

Fehling’s Test: Aliphatic aldehydes reduce blue $Cu^{2+}$ ions to reddish-brown $Cu_2O$. $R\text{-}CHO + 2Cu^{2+} + 5OH^- \rightarrow R\text{-}COO^- + Cu_2O \downarrow + ...$

Procedure

  1. Select a sample (Propanal or Propanone) to fill the test tubes.
  2. Add reagents (Tollen's ingredients or Fehling's A+B).
  3. Place tubes in the Water Bath at the bottom.
  4. Wait for the reaction (approx. 10s) and observe results.

Station 1: Sample Preparation

Ready
Propanal
Propanone
Tollen's
Fehling
TUBE 1
TUBE 2

Station 2: Hot Water Bath ($60^\circ\text{C}$)

Observation Log

Tube Sample Test Result

Experiment Monitor

Please add an organic sample to Tube 1 or Tube 2 to begin.

Ready