Distinguishing between Distinguishing between aldehydes and ketonesaldehydes and ketones

Can carbonyl compounds (and alcohols) Can carbonyl compounds (and alcohols) act as reductants and be oxidised?act as reductants and be oxidised?

Tollen’s testTollen’s test

1.1. Make Tollen’s reagent as follows:Make Tollen’s reagent as follows:Place 5 mL of 0.05 molLPlace 5 mL of 0.05 molL-1-1 silver nitrate in a tt and silver nitrate in a tt and add 1 drop dilute NaOH. Then SHAKING add 1 drop dilute NaOH. Then SHAKING THOROUGHLY between additions, add drops of THOROUGHLY between additions, add drops of dilute ammonia until the last of the ppte JUST dilute ammonia until the last of the ppte JUST disappears.disappears.

2. 2. Divide the Tollen’s reagent into 3 CLEAN tts.Divide the Tollen’s reagent into 3 CLEAN tts.

3. 3. Add 5 drops of ethanol, ethanal and Add 5 drops of ethanol, ethanal and propanone respectively.propanone respectively.

4. Place tt GENTLY in a water bath at 504. Place tt GENTLY in a water bath at 50°. °. Leave and observe.Leave and observe.

Benedict’s TestBenedict’s Test

1.1. To 5 mL of Benedict’s solution in a tt, To 5 mL of Benedict’s solution in a tt, add 5 drops of the test substance. add 5 drops of the test substance. Test ethanol, ethanal and propanone.Test ethanol, ethanal and propanone.

2.2. Heat to boiling CAREFULLY over a Heat to boiling CAREFULLY over a Bunsen Burner.Bunsen Burner.

QuestionsQuestions

1.1. Write an equation for the reaction of Write an equation for the reaction of ethanal with Tollen’s reagent.ethanal with Tollen’s reagent.

2.2. Write an equation for the reaction of Write an equation for the reaction of ethanal with Benedict’s reagent.ethanal with Benedict’s reagent.

AnswersAnswers

1.1. 2OH2OH-- + CH + CH33CHO CHO → CH→ CH33COOH + HCOOH + H22O O

+2e+2e

2Ag(NH2Ag(NH33))22++ + 2e → 2Ag + 4NH + 2e → 2Ag + 4NH33

2.2. Oxidation ½ equation is the sameOxidation ½ equation is the same

2Cu2Cu2+2+ + 2OH + 2OH-- + 2e → Cu + 2e → Cu22O + HO + H22O O