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Experiment ReportIdentifying the unknown carbonyl compound

By Kelvin Timotius and Manoel Manuputty (BrilliantClass Year 11 SMAK PENABUR Gading Serpong)

Introduction

There are some main types of functional group in Chemical compounds. FunctionalGroup is a part of chemical compound which determine chemical and physical properties of the compound. One of the most famous functional group in chemical compound is thecarbonyl group. We may be often meet any carbonyl compounds around us withoutrecognize it, such as nail polish, formalin, glue, etc. To find out the way to recognize acarbonyl compound, we have to determine some special properties of the compound anddesign a method to test it.

Carbonyl group consists of two sub-funtional groups, there are aldehyde and ketone.Basically, Aldehyde and Ketone have some different properties. The most basic differencebetween Aldehyde and Ketone groups is their ability to be oxidized by few chemicalreagents. Some oxidizers such as potassium dichromate (VI), potassium manganate (VI),fehling reagent, and tollens reagent ([Ag(NH3)2]OH) can be used as indicator for testing

aldehydes because they can oxidize the compound and give change in color and precipitatewhile they do not give any change after treating with ketones.

Furthermore, there is another method to determine structure of carbonyl compoundby testing it with Iod (I 2) in alkaline condition by adding NaOH (Sodium Hydroxide) whichcalled Iodoform test. Iodoform test is used to test methyl group in carbonyl or alcoholscompound.

Objectives

The goal of the experiment is to identify an unknown solution called solution X withsome information and different methods, also to learn about aldehyde and ketone tests(tollens and fehling).

Methods

From recent experiment, we knew that solution X cannot be oxidized, it also does notreact with iodoform test. What we did in this experiment was to determine whether thesolution X is a ketone or an aldehyde. So, in order to learn about the solution more, we didtollens and fehling tests. We also compared the results of the tollens and fehling tests of the solution X with those of the aldehyde (in this case formaldehyde).


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Identifying the unknown carbonyl compound

Tollens Test

Clean two test tubes with sodium hydroxide, and then wash them.

Add 2.5ml of silver nitrate 5% to each of the tube then add ammonia drop by dropuntil there is no precipitate.

Add 1 drop of sodium hydroxide 10%, if there is precipitate then add ammonia untilno more precipitate.

Add 5ml of solution X to one of the tube, and 5ml of formaldehyde to the other.

Heat the tubes!

Fehling Test

Clean three test tubes with sodium hydroxide, and then wash them.

Add 1 ml of fehling A and 1 ml of fehling B to one of the tubes, mix them.

Drop 1 ml of the fehling mixture to each of the tube (currently two tubes).

Add 5ml of solution X to one of the tube, and 5ml of formaldehyde to the other.

Heat the tubes!

Results

Identify Compound X

Compound X has boiling points about 56.5C. Weve done four tests on solution X:oxidation, fehling, tollens, and iodoform. Which result as:

OXIDATION TOLLENS FEHLING IODOFORM

NEGATIVE NEGATIVE NEGATIVE POSITIVE

No Change No Change No Change Yellow precipitate

From the boiling point information and result above, we can conclude that:

1. Compound X has neither alcohol nor aldehyde group (cant be oxidized)

2. Compound X has methyl group besides ketone group (iodoform test)

3. Compound X has relatively low boiling points which we can say that it has relativelyshort carbon chains and is a nonpolar/semipolar compound. For a comparisonethanol which has two carbon chains and is a polar molecule has boiling points about

78C.Since the probability only lead us to ketone group (acetone, buthan-2-on, etc), we couldconclude that the compound X is acetone (CH 3 COCH 3 ) , because ketones with longercarbon chains will have higher boiling points than ethanol which are incorrect.

Brilliant Class, BPK Penabur | [Kelvin and Noel]


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Fehling and Tollens Tests

From the fehling and tollens test which are tests to differ aldehydes and ketones, weknow that compound X is not an aldehyde since it was not react with tollens and fehling (nochange happen). But, how about the formaldehyde? The formaldehyde reacted with bothfehling and tollens. Which result as:

FEHLING TOLLENSRed-BrownPrecipitate

Silver mirror in thetest tube

Discussion

Q : What is main chemical property which explain ability of aldehyde compound to beoxidized while ketone is not?

A : Aldehyde compound has a Hydrogen carbonyl which is able to oxidized, whileketone has no one and it makes ketone is not able to oxidized.

Q : What happens when an aldehyde give silver mirror when treated with tollens reagentand give red-brown precipitate when treated with fehling solution?

A : When the aldehyde compound treated with tollens reagent, the followingchemical reaction occurs:

We could see that the reaction yields Silver precipitate (silver mirror). Whenaldehyde treated with Fehling solution, the following chemical reaction occurs:

In this case, Cu 2O is a red-brown precipitate.

Q : What is the difference between Fehling A and Fehling B?

A : Fehling A is a solution of Copper (II) Sulfate pentahydrate (69.28 grams in1 L of water), while fehling B is a solution of Rochelle salts (Potassium Sodiumtartrate tetrahydrate) and Sodium Hydroxide (NaOH) in distilled water (346grams of Rochelle salt, 120 grams of NaOH, and 1 L water)

Q : Why do we have to heat the tubes?



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A : Heating tubes was intended to accelerate the reaction between solutionsand reagents, especially for fehling test because it will need much more timeto react when not heated.

Q : How can we conclude that low boiling point of the unknown compound means that the

compound has relatively low molar mass or the compound is a non-polar or semipolarcompound?

A : Boiling point is affected by intermolecular forces in one compound. Whena compound has low boiling point, it means that the intermolecular forces isalso low. A polar compound, usually has high boiling point because thecompound has dipole force between it molecules and make it strong. Thatswhy we can conclude that the compound is a non-polar or semipolarcompound. Relatively low molar mass is also affect the low boiling point.

Q : Why cant we conclude that the compound was ethanol since we know that methylalcohol is also give positive result when treated with iodoform test?

A : Although ethanol is also give positive result when treated with iodoform test, butwe know that the unknown compound does not give positive result when oxidizedwhich means that it is not ethanol since we know that ethanol is easily oxidized toform acetic acid.

ConclusionAfter some chemical tests and compared with informations given, we could conclude thatthe compound X is acetone, which is a carbonyl compound especially ketone group.

References http://en.wikipedia.org (accessed : February 3 rd 2009)

http://www.google.co.id (accessed: February 3 rd 2009)

FEEDBACK

INTRODUCTION = introduction sudah bagus, hanya pengunaan SUBJECT biasanya dilarang,karena report itu bersifat universal. Tetapi ini kembali kepada kebijakan dosen dan kampus.Pada dasarnya, report yang baik adalah report yang bersifat universal.

OBJECTIVES =Padat, singkat, jelas. PERFECT

METHODS = Padat, singkat, jelas.PERFECT

RESULTS = Penyajian data sudah bagus dan dapat dimengerti

DISCUSSION = Diskusi experiment sudah detail dan sangat jelas

CONCLUSION = Padat , singkat , jelas. PERFECT

http://en.wikipedia.org/http://www.google.co.id/http://en.wikipedia.org/http://www.google.co.id/


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REFERENCES = references juga sudah bagus, karena cara penulisan references tergantungsama kebijakan sekolah/kampus, jadi dalam penulisannya boleh dengan format apa ajaselama itu masih berlagu ( e.g. Chicago Referencing, Harvard Referencing )

Please note : 1. Pengunaan SUBJECT kalau bisa dihindari. Bersifatlah universal

2. Sebagai saran dan masukan, WIKIPEDIA biasanya jarang dipake sebagai

referensi. Memang adabeberapa dosen yang suka dan ada yang ga suka, jadi tergantung samakebijakan kampus

dan dosennya ;)


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