How can aldehydes and ketones be distinguished?

MYTUTOR SUBJECT ANSWERS

Answers / Chemistry / A Level / How can aldehydes and ketones be distinguished?

2852 views

How can aldehydes and ketones be distinguished?

Firstly note that in general aldehydes are more reactive than ketones. This is a result of two effects:

1. Ketones are more sterically hindered.

2. Alkyl groups are electron donating and so reduce the partial positive charge on the carbonyl carbon.

As a consequence of this difference in reactivity aldehydes are oxidised more easily than ketones and so, by selecting a sufficiently weak oxidising agent, we can distinguish the two functional groups by oxidising one but not the other.

Fehling's Test

The test begins as two separate solutions - Fehling's A and Fehling's B. The first is a light blue CuSO₄solution while the second is a solution of a chelate and sodium hydroxide.

Equal volumes of the two solutions are mixed and the sample is added. The resulting solution is heated.

Aldehyde - The aldehyde is oxidised and a brick red Cu(I) oxide precipitates out,

Ketone - No reaction occurs.

The Silver Mirror Test

This test makes use of Tollen's reagent which contains the complex [Ag(NH₃)₂]⁺. It is easily made by mixing aqueous ammonia with aqueous silver nitrate.

Aldehyde - Upon heating with Tollen's reagent solid silver metal is produced as Ag⁺is reduced to Ag.

Ketone - No reaction occurs.

George B. A Level Chemistry tutor, GCSE Science tutor, GCSE Biology t...

2 years ago

Answered by George, an A Level Chemistry tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist

154 SUBJECT SPECIALISTS

Anh-Duong V. A Level Biology tutor, A Level Chemistry tutor, Mentorin...

View profile

£30 /hr

Anh-Duong V.

Degree: Medicine (Bachelors) - Bristol University

Subjects offered:Chemistry, Science+ 4 more

“I’m AD, a medical student at Bristol and I offer Biology, Chemistry and personal statement tutoring!”

5.0

81 reviews | 261 completed tutorials

Save profile

Darshana J. A Level Biology tutor, GCSE Biology tutor, A Level Chemis...

View profile

£24 /hr

Darshana J.

Degree: Medicine (Other) - Birmingham University

Subjects offered:Chemistry, Biology+ 2 more

“I am a first year medical student at the University of Birmingham. My teaching sessions will be tailored around each student, going at their pace.”

5.0

21 reviews | 38 completed tutorials

Save profile

Rama K. Uni Admissions Test .BMAT (BioMedical Admissions) tutor, A Le...

View profile

£26 /hr

Rama K.

Degree: MBChB (Bachelors) - Birmingham University

Subjects offered:Chemistry, Physics+ 5 more

“I am a passionate medical student who would love to teach the sciences and maths to any willing student! I would also love to help prospective medical students achieve their dreams!”

5.0

34 reviews | 113 completed tutorials

Save profile

See more A Level Chemistry tutors

About the author

View profile

£22 /hr

George B.

Degree: Chemistry (Masters) - Oxford, Jesus College University

Subjects offered:Chemistry, Science+ 3 more

“About Me: As a second year chemist at Oxford University I naturally have a love for anything and everything science. Science can be challenging at times however, with the right approach, it can be anengaging and exciting subject. I ho...”

5.0

2 reviews | 14 completed tutorials

Save profile

Version:	3.49.3
Build:	d44f18974ed8
Time:	2017-08-17T14:08:28Z

MYTUTOR SUBJECT ANSWERS

How can aldehydes and ketones be distinguished?

Still stuck? Get one-to-one help from a personally interviewed subject specialist

154 SUBJECT SPECIALISTS

About the author

You may also like...

Posts by George

Other A Level Chemistry questions

One-to-one help is at your fingertips