Transcript Bond angles - Nayland College

Distinguishing between aldehydes
and ketones
Can carbonyl compounds (and alcohols) act
as reductants and be oxidised?
Tollen’s test
1.
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.
Benedict’s Test
1.
2.
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.
Questions
1.
2.
Write an equation for the reaction of
ethanal with Tollen’s reagent.
Write an equation for the reaction of
ethanal with Benedict’s reagent.
Answers
1.
2OH- + CH3CHO → CH3COOH + H2O +2e
2Ag(NH3)2+ + 2e → 2Ag + 4NH3
2.
Oxidation ½ equation is the same
2Cu2+ + 2OH- + 2e → Cu2O + H2O