Laboratory Report 2 Qualitative Analysis OF Carboxylic Acids AND THE Derivatives PDF

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LABORATORY REPORT 2: QUALITATIVE ANALYSIS OF CARBOXYLIC ACIDS AND THE DERIVATIVES

NAME: NURHIKMA SYAKINA BINTI ZULKIFLEY CLASS: AS1204A2 MATRIX NO: 2018445326 COURSE: ORGANIC CHEMISTRY II COURSE CODE: CHM301 LECTURER: MADAM JULENAH AG NUDDIN DATE OF SUBMISSION: 15 MAY 2020

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1.0 INTRODUCTION The carboxyl group in chemistry is an organic, functional group consisting of a carbon atom that is double-bonded to an oxygen atom and singly bonded to a hydroxyl group. Figure 1 shows the structure of carboxyl group.

Figure 1 A carboxylic acid is an organic compound containing a carboxyl group (C(=O)OH). R – COOH, with R referring to the alkyl group, is the general formula of a carboxylic acid. The carbonyl carbon in carboxylic acids and derivatives is sp2 hybridized. Figure 2 shows the structure of carboxylic acid.

Figure 2 The boiling points of carboxylic acids increase as the molecules get bigger as they form dimers in which hydrogen bonds form between the polar groups in the two carboxyl groups. Carboxylic acids have even higher boiling points than alkanes and alcohols. They are also soluble in water due to hydrogen bonding. Figure 3 shows the boiling point and solubility of carboxylic acids.

Figure 3 Similar to alcohols, carboxylic acids can form hydrogen bonds with one another, as well as dispersion forces and dipole-dipole interactions and van der Waals. However, unique to carboxylic acids, hydrogen bonding may occur between two molecules to produce a dimer. The presence of dimers increases the strength of the dispersion forces in van der Waals, resulting in high boiling points of carboxylic acids. Figure 4 shows the hydrogen bonding of carboxylic acid.

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Figure 4 Carboxylic acid is strongly polar as they have two polar groups hydroxyl (-OH) and carbonyl (C=O). Figure 5 shows the polarity of carboxylic acid.

Figure 5

Carboxylic acids are the weak acids. In neutral aqueous solvents such as water, they partially dissociate into H+ cations and RCOO- anions. Next, c arboxylic acids undergo reactions to produce derivatives of the acid such as esters. Esters are derived when a carboxylic acid reacts with an alcohol. The acid-catalyzed esterification of carboxylic acids with alcohols to give esters is termed Fischer esterification. Figure 6 shows the mechanism of carboxylic acid in Fischer esterification.

Figure 6

2.0 AIM To investigate the reaction of carboxylic acids and its derivatives with certain reagents.

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3.0 METHODOLOGY 3.1 MATERIALS AND APPARATUS For

materials,

we

used

ethanoic

acid

solution(acetic

acid),

ethanamide

solid(acetanamide), 5% solution of Na2CO3, ethanol, diluted and concentrated sulphuric acid, NaOH solution, FeCl3 solution, sodium nitrite solution(NaNO2), and dilute HCl. For apparatus, we used test tubes, red litmus paper and blue litmus paper.

3.2 PROCEDURE

Method A: Reaction of ethanoic acid solution (acetic acid) with various reagents 2 ml of 5% solution Na2CO3 was poured in a watch glass and then 2-3 drops of ethanoic acid was added into it. The reaction was observed.

2 ml of ethanol and 3 drops of concentrated H2SO4 were added to a test tube. The mixture was heated in water bath for 5 minutes. The smell was recorded.

In order to prepare a neutral carboxylic acid salt, 3 ml of ethanoic acid solution was mixed with a few drops of NaOH. FeCl3 solution was prepared in a separate test tube with a few drops of NaOH until precipitation of iron(III) almost forms. The solution was filtered and the filtrate was used (the remaining solution). The two solutions were mixed. The neutral solution of carboxylic acid and FeCl3 solution were boiled. Any changes were recorded.

Method B: Reaction of carboxylic acid derivative solution- ethanamide (acetanamide) For base hydrolysis reaction, 0.2g of ethanamide and 2 ml of dilute NaOH were added into a test tube and then the mixture was heated. The gas evolve was identified.

For acid hydrolysis reaction, 0.2g of ethanamide and 2 ml of dilute H2SO4 were added into a test tube and then the mixture was heated. The gas evolve or any changes were identified.

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For Nitrogen acid solution (HNO2) reaction, 5g of ethanamide and then 3-4 ml of sodium nitrite (NaNO2) were added into test tube followed by a few drops of dilute HCl. The observation was recorded.

4.0 RESULTS

METHOD

OBSERVATION

A:

Reaction a)

Brisk effervescence formation which

of

ethanoic

indicates the presence of carboxylic acid

acid solution

b)

(acetic acid)

B:

Reaction

The sweet smells tend towards artificial fruit

Reaction of sodium carbonate Esterification of

flavouring like "pear drops" is formed.

ester

c)

A reddish brown colour is formed.

Hydrolysis of ester

a)

Red litmus paper turned into blue.

Hydrolysis under

of carboxylic

The gas is evolved due to the presence of ammonia

acid

gas.

derivative

REMARKS

b)

Blue litmus paper turned into red.

solutionethanamide

The gas is not evolved, ammonia sulfate is present.

(acetanamide) c)

A burst of colourless, odourless gas.

basic condition

Hydrolysis under acid condition Reaction of nitrous

The nitrogen gas is present.

acid

5.0 DISCUSSION Method A: Reaction of ethanoic acid solution (acetic acid) with various reagents a) Chemical Equation:

N  o brisk effervescence

Formation of brisk effervescence

The equation above is unbalanced but shows the hydrogen in the hydroxyl part of the carboxylic group is lost and replaced by the sodium. The resulting bond between the sodium and the

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ethanoate group is ionic. It must not be represented by a line between the two atoms as this would represent a covalent bond. Ethanoic acid reacts with sodium carbonate and produces sodium ethanoate, water and carbon dioxide. This reaction is called the reaction of sodium carbonate. The hydrogen in the hydroxyl part of the carboxylic group is lost and replaced with the metal of the salt in ethanoic acid. From the observation, the formation of brisk effervescence at the end of the reaction is due to formation of carbon dioxide.

b)Chemical Equation:

Formation of sweet smells like fruit flavoring In this reaction, ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid as a catalyst to produce the ester ethyl ethanoate and observe the smell of ester formed. This reaction is called an esterification of carboxylic acids. The reaction is slow and reversible. To reduce the chances of the reverse reaction occurring, the ester is distilled off as soon as it is formed. At the end of the reaction, the sweet smells tend towards artificial fruit flavouring like "pear drops" is formed. All the steps in the mechanism below are shown as one-way reactions because it makes the mechanism look less confusing. Step 1: In the first step, the ethanoic acid takes a proton (a hydrogen ion) from the concentrated sulphuric acid. The proton becomes attached to one of the lone pairs on the oxygen which is double-bonded to the carbon. The transfer of the proton to the oxygen gives it a positive charge. The positive charge is delocalised over the whole of the right-hand end of the ion, with a fair amount of positiveness on the carbon atom.

One way of writing the delocalised structure of the ion is like this:

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Step 2: The positive charge on the carbon atom is attacked by one of the lone pairs on the oxygen of the ethanol molecule.

Step 3: What happens next is that a proton (a hydrogen ion) gets transferred from the bottom oxygen atom to one of the others. It gets picked off by one of the other substances in the mixture (for example, by attaching to a lone pair on an unreacted ethanol molecule), and then dumped back onto one of the oxygens more or less at random.

Step 4: Now a molecule of water is lost from the ion.

The structure for the latest ion is just like the that discussed at length back in step 1. The positive charge is actually delocalised all over that end of the ion, and there will also be contributions from structures where the charge is on the either of the oxygen:

Step 5: The hydrogen is removed from the oxygen by reaction with the hydrogensulphate ion which was formed way back in the first step.

The ester has been formed, and the sulphuric acid catalyst has been regenerated.

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c)(i)Chemical Equation: CH3COOH + NaOH →   CH3COONa + H2O Sodium ethanoate In this reaction, aqueous ethanoic acid is a carboxylic acid. Reaction of ethanoic acid and aqueous NaOH is a weak acid-strong base reaction. W  hen ethanoic acid (weak acid) with a sodium hydroxide (strong base) are being neutralized, a sodium ethanoate (salt) that contains the conjugate base of the weak acid and water are given as products. This conjugate base is usually a weak base. The product from this reaction will be used in (c)(iii) reaction. (ii)Chemical Equation: FeCl3 + 3NaOH →   Fe(OH)3 + 3NaCl Yellow-brown

Brown colour precipitate

Based on the equation, I ron(III) chloride reacts with sodium hydroxide to form iron(III) hydroxide

 ence, yellow-brown color solution will turn into a brown color precipitate. and sodium chloride. H This precipitate is iron(III) hydroxide, Fe(OH)3. T  he solution (product) then undergoes the filtration process to separate solid from liquid. FeCl3 solution is formed as a filtrate(the remaining solution) and will be used in (c)(iii) reaction.

(iii)Chemical Equation: FeCl3 + 3CH3COONa →   Fe(CH3COO)3 + 3NaCl This equation shows the hydrolysis of ester reaction. Firstly, sodium ethanoate together with the filtrate, will react to the ferric ion. Sodium ethanoate will be neutralized and will become acetate so that sodium hydroxide will be the one reduced and not sodium ethanoate. Acetate will then react with Ferric Chloride, producing Ferric acetate which has a visible result present in the experiment. Hence, a reddish brown colour is formed from the reaction.

Method B: Reaction of carboxylic acid derivative solution- ethanamide (acetanamide) a) Chemical Equation: CH3CONH2 + NaOH →   CH3COONa + NH3 Ammonia gas has evolved When ethanamide is heated with NaOH, ammonia gas is given off and left with a solution containing sodium ethanoate. Ammonia gas has evolved. With the addition of NaOH, the color of the red litmus paper turns blue which indicates the basicity of the substance since ammonia was formed. Nitrogen atom in the molecule has a lone pair making it a proton acceptor. Their aqueous solutions are basic because amine acts as weak bases by accepting protons from water and producing hydroxide ions. 8

b) Chemical Equation: 2CH3CONH2 + H2SO4 + 2H2O →   2CH3COOH + (NH4)2SO4 Formation of ammonium sulfate Ethanamide(weak base) heated with a dilute H2SO4(strong base) is formed together with ammonium ions .The product of solution would contain ammonium sulfate and acetic acid. Ammonia did not evolve, ammonium sulfate is present. With the addition of HCl on ethanamide, it smelled like vinegar since acetic acid was formed. The color of the blue litmus paper changed to blue due to acetic acid formation. This reaction gives the product a pH which is less than 7. This  is due to the fact that the anion will become a spectator ion and fail to attract the H+, while the cation from the ethanamide will donate a proton to the water forming a hydronium ion.

c) Chemical Equation: HCl + NaNO2 →   HNO2 + NaCl Nitrous acid is unstable and must be prepared in the reaction solution by mixing sodium nitrite with acid. The equilibrium position lies towards right because nitrous acid is a weak acid. In every reaction, the amine is acidified with hydrochloric acid adding a solution of sodium nitrite. The nitrite and the acid form nitrous acid which reacts with the amine. Chemical Equation: CH3CONH2 + HNO2 →   CH3CHO2 + H2O + N2 Nitrogen gas is evolved When an ethanamide reacts with nitrous acid, the product is acetic acid, water and dinitrogen but the more interesting part about this reaction is that nitrogen gas is liberated as well. This reaction is called a reaction of nitrous acid. Thus, once the reaction happens the solution will start to bubble, kind of like a soda, as the nitrogen gas is evolved. A burst of colourless, odourless gas is formed.

6.0 CONCLUSION In conclusion, different reaction can be used for investigating the reaction of carboxylic acids and its derivatives with certain reagents based on method A and B. For method A, we use the reaction of carboxylic acids which are the sodium carbonate, esterification of carboxylic acid and hydrolysis of ester. For method B, we use base hydrolysis, acid hydrolysis and reaction of nitrous acid. Hence, the aim of the experiment is achieved.

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https://www.toppr.com/ask/question/the-reaction-of-ethanol-with-conc-h2so4-gives/ 6. Libretexts. (2019, June 05). Alkenes from Dehydration of Alcohols. Retrieved May 11, 2020, from https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic _Chemistry)/Alkenes/Synthesis_of_Alkenes/Alkenes_from_Dehydration_of_Alcohols 7. Nipuna,

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