Modul - Eksperimen 10

7/18/2019 Modul - Eksperimen 10

http://slidepdf.com/reader/full/modul-eksperimen-10 1/11

Experiment 10PROPERTIES OF CARBOXYLIC

ACIDS AND ESTERSI. OBJECTIVES

• To study the physical and chemical properties of carboxylic acids: solubility, acidity,

aroma.

• To prepare a variety of esters and note their odors.

• To demonstrate saponification.

II. INTRODUCTION

Carboxylic acids are structurally like aldehydes and ketones in that they contain the

carbonyl group. However, an important difference is that carboxylic acids contain a hydroxyl

group attached to the carbonyl carbon.

The carboxylic acid group

This combination gives the group its most important characteristic; it behaves as an acid.

s a family, carboxylic acids are weak acids that ioni!e only slightly in water. s

a"ueous solutions, typical carboxylic acids ioni!e to the extent of only one percent or less.

t e"uilibrium, most of the acid is present as un#ioni!ed molecules. $issociation constants,

%a, of carboxylic acids, where & is an alkyl group, are '( #) or less. *ater solubility depends

to a large extent on the si!e of the &#group. +nly a few low#molecular#weight acids up to

four carbons- are very soluble in water.

lthough carboxylic acids are weak, they are capable of reacting with bases stronger

than water. Thus while ben!oic acid shows limited water solubility, it reacts with sodium

hydroxide to form the soluble salt sodium ben!oate. odium ben!oate is a preservative in

soft drinks.- odium carbonate, /a0C+1, and sodium bicarbonate, /aHC+1, solutions can

neutrali!e carboxylic acids also.



The combination of a carboxylic acid and an alcohol gives an ester; water is

eliminated. 2ster formation is an e"uilibrium process, cataly!ed by an acid catalyst.

The reaction typically gives 3(4 to 5(4 of the maximum yield. The reaction is a reversible

process. n ester reacting with water, giving the carboxylic acid and alcohol, is called

hydrolysis; it is acid cataly!ed. The base#promoted decomposition of esters yields an alcohol

and a salt of the carboxylic acid; this process is called saponification. aponification means

6soap making,7 and the sodium salt of a fatty acid e.g., sodium stearate- is a soap.

distinctive difference between carboxylic acids and esters is in their characteristic

odors. Carboxylic acids are noted for their sour, disagreeable odors. +n the other hand, esters

have sweet and pleasant odors often associated with fruits, and fruits smell the way they do

because they contain esters. These compounds are used in the food industry as fragrances and

flavoring agents. 8or example, the putrid odor of rancid butter is due to the presence of

butyric acid, while the odor of pineapple is due to the presence of the ester, ethyl butyrate.

+nly those carboxylic acids of low molecular weight have odor at room temperature. Higher#

molecular#weight carboxylic acids form strong hydrogen bonds, are solid, and have a low

vapor pressure. Thus few molecules reach our noses. 2sters, however, do not form hydrogen

bonds among themselves; they are li"uid at room temperature, even when the molecular

weight is high. Thus they have high vapor pressure and many molecules can reach our noses,

providing odor.



III. EQUIPMENT & CHEMICALS

III.1. Equipment

'. pH paper broad range pH '9'0-

0. itmus paper

1. asteur pipet

<. Hot plate

III.. C!emi"#$%

'. Concentrated H0+<

0. =lacial acetic acid

1. >en!oic acid

<. 8ormic acid

). alicylic acid

3. >en!yl alcohol

5. 2thanol ethyl alcohol-?. 0#@ethyl#'#propanol isobutyl alcohol-

A. 1#@ethyl#'#butanol isopentyl alcohol-

'(. @ethanol methyl alcohol-

''. @ethyl salicylate

'0. 1 @ HCl

'1. 3 @ HCl

'<. 0 @ /a+H

'). 3 @ /a+H

IV. PROCEDURES

IV.1. C#'()*$i" A"i+% #n+ T!ei S#$t%

IV.1.1. C!##"tei%ti"% (, #"eti" #"i+

'. lace into a clean, dry test tube '(( x '1 mm- 0 m of water and '( drops of glacial

acetic acid. /ote its odor by wafting moving your hand "uickly over the open end of

the test tube- the vapors toward your nose. +f what does it remind youB

0. Take a glass rod and dip it into the solution. sing wide#range indicator paper pH '9

'0-, test the pH of the solution by touching the paper with the wet glass rod.$etermine the value of the pH by comparing the color of the paper with the chart on

the dispenser.

1. /ow, add 0 m of 0 @ /a+H to the solution. Cork the test tube and sharply tap it

with your finger. &emove the cork and determine the pH of the solution as before; if

not basic, continue to add more base dropwise- until the solution is basic. /ote the

odor and compare to the odor of the solution before the addition of base.

<. >y dropwise addition of 1 @ HCl, carefully reacidify the solution from step no. 1

above-; test the solution as before with pH paper until the solution tests acid. $oes

the original odor returnB



IV.1.. C!##"tei%ti"% (, 'en-(i" #"i+

'. Dour instructor will weigh out (.' g of ben!oic acid for sample si!e comparison. *ith

your microspatula, take some sample e"uivalent to the preweighed sample an exact

"uantity is not important here-. dd the solid to a test tube '(( x '1 mm- along with

0 m of water. Es there any odorB @ix the solution by sharply tapping the test tube

with your finger. How soluble is the ben!oic acidB

0. /ow add ' m of 0 @ /a+H to the solution from step no. ' above-, cork, and mix

by sharply tapping the test tube with your finger. *hat happens to the solid ben!oic

acidB Es there any odorB

1. >y dropwise addition of 1 @ HCl, carefully reacidify the solution from step no. 0

above-; test as before with pH paper until acidic. s the solution becomes acidic,

what do you observeBIV.. E%tei"#ti(n

'. Ento five clean, dry test tubes '(( x '1 mm-, add '( drops of li"uid carboxylic acid

or (.' g of solid carboxylic acid and '( drops of alcohol according to the scheme in

Table ).'. /ote the odor of each reactant.

0. dd ) drops of concentrated sulfuric acid to each test tube and mix the contents

thoroughly by sharply tapping the test tube with your finger.[Caution: Sulfuric acid causes severe burns. Flush any spill with lots of water. Use gloves with

thisreagent.]1. lace the test tubes in a warm water bath at 3(+C for ') min. &emove the test tubes

from the water bath, cool, and add 0 m of water to each. /ote that there is a layer on

top of the water in each test tube. *ith a asteur pipet, take a few drops from this top

layer and place on a watch glass. /ote the odor. @atch the ester from each test tube

with one of the following odors: banana, peach, raspberry, nail polish remover,

wintergreen.

Table 1.1 cids and lcohols

Test Tube

!o.

Carbocylic

"cid"lcohol

' 8ormic Esobutyl

0 cetic >en!yl

1 cetic Esopentyl

< cetic 2thyl

) alicylic @ethyl

IV./. S#p(ni"#ti(n

This part of the experiment can be done while the esterification reactions are being heated.



'. lace into a test tube ')( x '? mm- '( drops of methyl salicylate and ) m of 3 @

/a+H. Heat the contents in a boiling water bath for 1( min. &ecord on the &eport

heet what has happened to the ester layer '-.

0. Cool the test tube to room temperature by placing it in an ice water bath. $etermine

the odor of the solution and record your observation on the &eport heet 0-.

1. Carefully add 3 @ HCl to the solution, ' m at a time, until the solution is acidic.

fter each addition, mix the contents and test the solution with litmus. *hen the

solution is acidic, what do you observeB *hat is the name of the compound formedB

nswer these "uestions on the &eport heet 1-.

V. POTENTIAL HA0ARDS

#$S%&

' Fery ha!ardous in case of skin contact corrosive, irritant, permeator-, of eye

contact irritant, corrosive-, of ingestion, of inhalation. i"uid or spray mist may

produce tissue damage particularly on mucous membranes of eyes, mouth and

respiratory tract.

' *ear chemical safety goggles, protective gloves, and clothing to prevent

exposure.

(lacial acetic acid

' Causes severe irritation and burns. @ay >e harmful if swallowed. void breathing

vapor or dust. se with ade"uate ventilation. void contact with eyes, skin, and

clothes. *ash thoroughly after handling. %eep container closed.


exposure.

)en*oic acid

' Ha!ardous in case of skin contact irritant-, of eye contact irritant-, of ingestion,

of inhalation. lightly ha!ardous in case of skin contact permeator-.


exposure.

For+ic acid

' Fery ha!ardous in case of skin contact irritant-, of eye contact irritant,

corrosive-, of ingestion, . Ha!ardous in case of skin contact corrosive,

permeator-.


exposure.

Salicylic acid



' Ha!ardous in case of skin contact irritant-, of eye contact irritant-, of ingestion,

of inhalation lung irritant-. lightly ha!ardous in case of skin contact permeator-.

evere over#exposure can result in death.


exposure.

)en*yl alcohol

' Ha!ardous in case of skin contact irritant-, of eye contact irritant-, of inhalation.

lightly ha!ardous in case of skin contact permeator-, of ingestion.


exposure.

,thanol

' 8lammable li"uid and vapor. Cause severe eye irritation and moderate skin

irritation.

' *ear protective clothing and masker to prevent exposure.

-ethanol +ethyl alcohol/

' Toxic by ingestion and inhalation. Can be toxic by skin absorption.ffects central

nervous system, especially optic nerve.Causes di!!iness, nausea, muscle

weakness, narcosis, respiratory failure.rolonged or repeated skin contact may

cause irritation.

' *ear safety glasses, protective clothing and masker to prevent exposure

#Cl

' Corrosive to skin, eyes, nose mucous membranes, respiratory G gastrointestinal

tract. Enhalation:respiratory tract irritationinfection. evere G fatal

gastrointestinal burns wnecrosis. evere burns to eyes G blindness. Changes in

pulmonary function, chronic bronchitis,dermatitis, tooth erosion, G conIunctivitis.

' *ear splash chemical goggles , protective gloves, and clothing to prevent exposure.

!a%#

' @ucous membrane irritant. kin: severe irritation, sensiti!ation, dermatitis G burns.

2yes: irritation,conIunctivitisG burns. Engestion: damage to mucous membranes or

tissues.

' *ear protective gloves, and clothing to prevent exposure.

VI. QUESTIONS AND PROBLEMS

VI.1. PeL#' Que%ti(n%

'. *rite the structures of the following carboxylic acids:

a- acetic acid b- formic acid



c- salicylic acid

0. *rite the products from the reaction of ben!oic acid and sodium hydroxide.

1. +ctylformate has the flavor of oranges. /ame the alcohol and the carboxylic acid

needed to synthesi!e this ester.

<. *hat is a 6soap7B

VI.. P(%tL#' Que%ti(n%

'. How do carboxylic acids and esters differ in their characteristic odorsB

0. *rite e"uations for each of the five esterification reactions.

1. >en!oic acid and diphenyl ketone are both insoluble in water. uggest a method for

separating a mixture of these compounds.

VII. REPORT 2ORMAT

/ame JJJJJJJJJJJJJJ $ate JJJJJJJJJJJJJJ

artnerJJJJJJJJJJJJJJ ab. ssistant JJJJJJJJJJJJJJ

0,%0T S#,,T

Carbo2ylic acids and their salts

Characteristics of "cetic "cid

roperty *ater olution /a+H olutionHCl

olution

+dor

olubility

pH

Characteristics of )en*oic "cid

roperty *ater olution /a+H olutionHCl

olution

+dor

olubility

pH

,sterification

Test Tube "cid %dor "lcohol %dor ,ster %dor



1

$

3

&

45



/ame JJJJJJJJJJJJJJ $ate JJJJJJJJJJJJJJ

artnerJJJJJJJJJJJJJJ ab. ssistant JJJJJJJJJJJJJJ

0,%0T S#,,T

Saponification

'. *hat has happened to the ester layerB

0. *hat has happened to the odor of the esterB

1. *hat forms on reacidification of the solutionB /ame the compound.

<. *rite the chemical e"uation for the saponification of methyl salicylate



otensi )ahaya

K H0+<

# angat berbahaya dalam kasus kontak kulit korosif, mengiritasi, permeator-, kontak mata

iritan, korosif-, menelan, inhalasi. Cair atau kabut semprotan dapat menghasilkan kerusakan

Iaringan terutama pada selaput lendir mata, mulut dan saluran pernapasan.

# %acamata keselamatan *ear kimia, sarung tangan pelindung, dan pakaian untuk mencegah

paIanan.

K asam asetat glasial

# @enyebabkan iritasi parah dan luka bakar. @ungkin berbahaya Iika tertelan. Hindari

menghirup uap atau debu. =unakan dengan ventilasi yang memadai. Hindari kontak dengan

mata, kulit, dan pakaian. Cuci sampai bersih setelah menangani. impan wadah tertutup.


paIanan.

K sam ben!oat

# >erbahaya dalam kasus kontak kulit iritan-, kontak mata iritan-, menelan, inhalasi. edikit

berbahaya dalam kasus kontak kulit permeator-.


paIanan.

K sam format

# angat berbahaya dalam kasus kontak kulit iritan-, kontak mata iritan, korosif-, menelan,.

>erbahaya dalam kasus kontak kulit korosif, permeator-.


paIanan.

K sam salisilat

# >erbahaya dalam kasus kontak kulit iritan-, kontak mata iritan-, menelan, inhalasi paru#

paru iritan-. edikit berbahaya dalam kasus kontak kulit permeator-. arah over#exposure

dapat mengakibatkan kematian.


paIanan.

K >en!il alkohol

# >erbahaya dalam kasus kontak kulit iritan-, kontak mata iritan-, inhalasi. edikit

berbahaya dalam kasus kontak kulit permeator-, menelan.




paIanan.

K 2tanol

# Cairan dan uap yang mudah terbakar. @enyebabkan iritasi mata dan iritasi kulit moderat.

# %enakan pakaian pelindung dan masker untuk mencegah paIanan.

K @etanol metil alkohol-

# Toxic oleh konsumsi dan inhalasi. $apat menIadi racun oleh absorption.ffects kulit sistem

saraf pusat, terutama optik nerve.Causes pusing, mual, kelemahan otot, narkosis,

failure.rolonged pernapasan atau kontak kulit berulang dapat menyebabkan iritasi.

# =elas *ear keselamatan, pakaian pelindung dan masker untuk mencegah paIanan

K HCl

# %orosif terhadap kulit, mata, selaput lendir hidung, pernapasan G saluran pencernaan.

Enhalasi: iritasi saluran pernapasan infeksi. arah G mematikan gastrointestinal membakar

w nekrosis. uka bakar yang parah mata G kebutaan. erubahan fungsi paru, bronkitis

kronis, dermatitis, erosi gigi, G konIungtivitis.

# %acamata *ear percikan kimia, sarung tangan pelindung, dan pakaian untuk mencegah

paIanan.

K /a+H

# endir membran iritasi. %ulit: parah iritasi, sensitisasi, dermatitis G luka bakar. @ata:

iritasi, konIungtivitis G luka bakar. Tertelan: kerusakan membran mukosa atau Iaringan.

# akailah sarung tangan pelindung, dan pakaian untuk mencegah paIanan.

Modul - Eksperimen 10

Documents

Transcript of Modul - Eksperimen 10