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Distinguishing between aldehydes and ketones

Distinguishing between aldehydes and ketones. Can carbonyl compounds (and alcohols) act as reductants and be oxidised?. Tollen’s test. Make Tollen’s reagent as follows:

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Distinguishing between aldehydes and ketones

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  1. Distinguishing between aldehydes and ketones Can carbonyl compounds (and alcohols) act as reductants and be oxidised?

  2. Tollen’s test • Make Tollen’s reagent as follows: Place 5 mL of 0.05 molL-1 silver nitrate in a tt and add 1 drop dilute NaOH. Then SHAKING THOROUGHLY between additions, add drops of dilute ammonia until the last of the ppte JUST disappears. 2. Divide the Tollen’s reagent into 3 CLEAN tts. 3. Add 5 drops of ethanol, ethanal and propanone respectively. 4. Place tt GENTLY in a water bath at 50°. Leave and observe.

  3. Benedict’s Test • To 5 mL of Benedict’s solution in a tt, add 5 drops of the test substance. Test ethanol, ethanal and propanone. • Heat to boiling CAREFULLY over a Bunsen Burner.

  4. Questions • Write an equation for the reaction of ethanal with Tollen’s reagent. • Write an equation for the reaction of ethanal with Benedict’s reagent.

  5. Answers • 2OH- + CH3CHO → CH3COOH + H2O +2e 2Ag(NH3)2+ + 2e → 2Ag + 4NH3 • Oxidation ½ equation is the same 2Cu2+ + 2OH- + 2e → Cu2O + H2O

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