CY 103P: Chemistry Laboratory Manual
Department of Chemistry
Indian Institute of Technology Tirupati
Tirupati - 517 506
2024 – 2025
FOREWORD
In the 21st century, sustained efforts on new innovations and developments in
materials science and technology have made and continue to make remarkable
contributions to the needs and material comforts of our society. Understanding
and learning the underlined chemistry of materials at the fundamental level
primarily plays an unprecedented role in advancing modern science and
technology-based innovations.
In this regard, laboratory experiments provide an efficient and effective
hands-on learning environment. Experience of experimentation is a delightful
way of appreciating concepts and consequences of chemistry and its applicability.
The experiments included in this manual have been carefully designed and
developed by a dedicated team from our department with a view to providing an
opportunity to the young and enthusiastic first-year undergraduate students, a
taste of experimental chemistry, its range, variety, principles underlying in them
and utility value.
We thank profusely the entire team of colleagues who always work hard to
reach out this goal. We wish all the student participants a useful and an enjoyable
experience in learning chemistry through practical experimentation and
demonstration.
Department of Chemistry
ii
Contents
Expt.
No.
Title
Page
No.
Cycle - I
1.
2.
3.
4.
Quantitative analysis: Gravimetric estimation of nickel(II)
as dimethylglyoximate complex
Volumetric analysis: Preparation of potassium bis
(oxalato)cuprate(II) dihydrate complex and volumetric
estimation of oxalate content in the complex
Organic synthesis: Preparation and purification of aspirin –
an analgesic drug
Water Quality: Hardness in water by complexometry
1
5
9
12
Cycle – II
5.
Selective extraction: Extraction of caffeine from tea leaves 15
6.
Colorimetric estimation: Copper content in Brass by 19
colorimeter
Conductivity meter: Acid strength of citrus fruit juices by 23
conductometer
Reaction Kinetics: Ester hydrolysis
27
7.
8.
i
Laboratory Safety:
“Safety FIRST, Rest is only NEXT”
Personal Safety Practices
 If anything gets in your eyes or skin or clothes, immediately rinse with plenty
of water and notify to your supervisor.
 Dress appropriately on lab working day, tie back long hair and don’t wear
dangling jewellery.
In the event of Fire:
1. Leave the building immediately
2. Never use lifts
Wash hands before leaving the lab
Fire safety (know the locations)
Emergency shower
Eye wash fountain
iii
Fire extinguisher
iv
Key Instructions (Strict adherence required)
 Lab dress is a must [lab coat(full sleeve), proper dress, safety goggles, shoes,
hand gloves and head mask (if required)].
 Know and plan your work (If not known, ask first to know).
 Know location of the safety devices [Eye wash fountain, shower area, fire
blanket and fire extinguisher].
 Eating, drinking and smoking – strictly prohibited in the lab.
 No food is allowed to be stored in the lab refrigerator.
 No running around and cross talks in the lab.
 Report any unsafe practice of your labmate immediately without any
hesitation to prevent damage.
 Never leave your work unattended in the lab.
 Keep fume hood and your work area clean always and maximize your work
space.
 Lab waste disposal should be proper and as per instructions [not into sink or
drainage!!].
 Never work alone in the laboratory.
 Mobile phones and music headphones are strictly prohibited in the laboratory.
v
Experiment: 1
QUANTITATIVE ANALYSIS: Gravimetric Estimation
of Nickel (II) as its Dimethylglyoximate Complex
Aim:
To quantitatively estimate the amount of Ni2+ ions in the given sample by
gravimetric method.
Principle:
Nickel ions form stable chelating complex with dimethylglyoxime (DMG).
Amount of nickel ions can be estimated by precipitating with DMG as Ni2+-DMG
complex.
Glasswares/Apparatus required:
Analytical balance
Beaker (500 mL) with glass rod (1 no.)
Pipette (20 mL, 1 no.)
Watch glass
Measuring Cylinder (10 mL, 1 no.)
Sintered crucible
Dessicator with anhydrous CaCl2
1
Chemicals required:
DMG solution (1% in absolute ethanol) (10-12 mL)
1:1 Hydrochloric acid (6 mL)
Ammonia solution (dilute) (25 mL/excess)
1:100 very dilute ammonia (for washing)
Procedure:
Nickel is precipitated by the addition of an ethanolic solution of 1%
dimethylglyoxime (DMG) to a hot, faintly acidic solution of the nickel salt and
then adding a slight excess of dilute ammonia solution(1:10) (free from
carbonate). The pink/purple colored Ni2+-DMG complex precipitate is filtered,
washed dried and weighed for constant weight.
1. Transfer exactly ~20 mL of the given unknown nickel solution into 500
mL beaker using a pipette. Cover the beaker with a watch glass.
2. Add ~5 mL of 1:1 HCl and dilute it to 200 mL.
3. Heat the solution to ~70-80 oC on a hot plate, add a slight excess (~ 12-15
mL) of the dimethyl glyoxime reagent and immediately add dilute
ammonia solution with constant stirring until precipitation takes place.
4. Allow this to stand on hot water bath for 15 minutes.
5. Cool to room temperature and filter through pre-weighed G-3 (pore size =
15-40 microns).
6. Sintered crucible (empty weight of the crucible to be taken first using
analytical balance only).
7. Keep the sintered crucible in the suction setup and wash it by draining ~20
mL of very dilute ammonia (1:100) solution through it by applying
vacuum. Then transfer the precipitate quantitatively into the sintered
crucible carefully without any loss.
8. Wash the precipitate with very dilute 1:100 ammonia and then with cold
2
water (Use minimum amount of water).
9. Dry it at ~110-120 oC for 30-40 minutes.
10. Cool the crucible in dessicator and then weigh the crucible with
precipitate. Repeat until constant weight is attained.
11. Weigh the complex Ni(C4H7O2N2)2, which contains 20.32% Ni2+.
3
Experiment: 2
VOLUMETRIC ANALYSIS: Preparation of Potassium
Bis(oxalato)cuprate(II)
dihydrate
Complex
and
Volumetric Estimation of its Oxalate Content
Aim:
To prepare potassium bis(oxalato)cuprate(II) dihydrate and determination of its
oxalate content by volumetric analysis.
Principle:
Copper(II) is precipitated as its bis oxalato complex by the addition of hot
aqueous solution of sodium oxalate (Na2C2O4) to a warm solution of
CuSO4.5H2O. In the oxalate complex, the oxalate behaves as a bidentate ligand
and the complex remains in dissolved state at higher temperatures and on cooling
it to < 10oC, precipitation occurs.
In acid solution, permanganate, MnO4- [Mn(VII)] is reduced to Mn(II). The
half reaction is:
In basic or neutral solution, permanganate, MnO4- [Mn(VII)] is reduced to
Mn(IV). The half reaction is:
Sodium oxalate or oxalic acid is often used to standardize permanganate. The
relevant half reaction is:
Therefore the reaction with permanganate is favourable, i.e.,
5
Reaction scheme:
Glassware required:
Beaker with glass rod (100 mL, 2 no.)
Sintered crucible (G-3, 1 no.)
Conical flask (250 mL, 1 no.)
Burette (50 mL, 1 no.)
Chemicals required:
(Note: use only preparative balance)
Copper sulphate solid (2 g)
Potassium oxalate solid (6 g)
Acetone (for washing)
Sulphuric acid (4N) – 10 mL
Potassium permanganate solution (0.05N) – 100 mL
Procedure:
1. Dissolve ~2 g of CuSO4.5H2O in 5 mL water and heat the solution to
70 (use preparative balance to weigh the starting materials).
2. In a separate beaker, add 6 g of K2C2O4.H2O to 20 mL of water and
heat the contents to dissolve completely.
3. Add slowly, warm solution of copper sulphate to oxalate solution with
slow stirring and then allow the hot solution to cool.
4. Filter the precipitate through a sintered (G-3) crucible and wash with
6
ice cold water (5 mL or minimum), followed by ice cold acetone. Dry
the product at 60-70 oC (for about 20 minutes) in a hot air oven.
Analysis:
1. Weigh accurately about 0.1 g (use analytical balance) of the dried
copper oxalate complex and transfer into a conical flask.
2. Add 10 mL of 4N H2SO4, dilute to 50 mL and heat the contents of the
flask to boiling.
3. Titrate the hot solution with 0.05N KMnO4 and note the end point
which is the appearance of permanent pink color.
1000 mL 1N KMnO4
≡
44.01 g of C2O42-
Wc = Weight of copper oxalate complex taken; NKMnO4 = Normality of
KMnO4; V KMnO4 = Volume of KMnO4
7
Experiment: 3
ORGANIC SYNTHESIS: Preparation and Purification
of Aspirin – an Analgesic Drug
Aim:
To prepare aspirin (acetylsalicylic acid) from salicylic acid using acetic anhydride
and acetic acid.
Theory:
The synthesis of aspirin is an example of an esterification reaction. Salicylic acid
is a phenol as well as a carboxylic acid. It can, therefore, undergo two different
types of esterification reactions, creating an ester either with the hydroxyl group
or with the acid group. In the presence of catalytic amounts of sulphuric acid,
acetic anhydride reacts with the phenolic OH of salicylic acid because of its
nucleophilicity to form acetylsalicylic acid (aspirin or ASA).
Reaction:
Materials Required:
Erlenmeyer Flask (100 mL)
Measuring Cylinder (25 mL)
Measuring Cylinder (10 mL, 1 no.)
Measuring Cylinder (5 mL, 1 no.)
9
Beaker (50 mL)
Graduated Pipette (1 mL)
Chemicals Required:
Salicylic acid (1.0 g)
Acetic anhydride (2.0 mL)
Acetic acid (2.0 mL)
Conc. Sulphuric acid (0.1 mL)
Ethanol (10 mL)
Procedure:
i.
Take 0.5 g of salicylic acid in a 100 mL Erlenmeyer flask.
ii.
Add 2.0 mL of acetic acid to dissolve the salicylic acid and keep the
flask in an ice bath (just to cool, avoid precipitation) inside the fume
hood.
iii.
Add dropwise 2.0 mL of acetic anhydride to the dissolved salicylic acid
with stirring, then continue stirring for about 10 min using a glass rod
(addition should be done inside the fume hood). Add 0.1 mL (2 drops)
of conc. H2SO4 to the solution and stir the reaction mixture for another
2 min.
iv.
Add 15 mL of cold distilled water to the reaction mixture and heat to
60 oC on a hot plate for complete dissolution (careful heating, don’t turn
it to brown or yellow).
v.
Cool to room temperature. Keep the flask in an ice-bath until crystals
begin to form. Filter the mixture, wash the crystals with cold distilled
water and dry between pieces of filter paper.
vi.
Transfer the crystals into a 50 mL beaker. Add 10 mL of ethanol and 10
mL of water. Heat the mixture until all the ethanol evaporates (volume
reduced to half).
vii.
Cool the solution to room temperature and keep in an ice-bath so as to
induce crystallization
10
viii.
Filter the solution. Wash the crystals with cold distilled water. Dry the
crystals between pieces of filter paper, weigh and calculate the % yield.
Hints:
i.
Theoretical yield = 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 ×
ii.
% Yield =
× 𝑀𝑊 𝑜𝑓 𝑃𝑟𝑜𝑑𝑢𝑐𝑡
.
× 100
11
Experiment: 4
WATER
QUALITY:
Hardness
in
Water
by
Complexometry
Aim:
To determine the permanent and temporary hardness of the given water
sample
by
complexometric
titration
using
standardized
ethylenediaminetetraacetic acid (EDTA) as titrant.
Principle:
Sodium or potassium salt of EDTA form a highly soluble 1:1 chelated
complexes with most metal ions, binding through
four oxygen and two nitrogen atoms (as shown in
figure). Water hardness is nothing but a measure of
the amount of calcium and magnesium salts
dissolved in water. Calcium and Magnesium ions
develop wine red colour with Eriochrome black-T
(EBT) indicator in aqueous alkaline solution (pH
10.0 ± 0.1). Thus, the water hardness can easily be
Fig. Metal-EDTA
determined by titrating the water sample with EDTA in alkaline condition. Hence
when EDTA is added as a titrant, these divalent Calcium and Magnesium ions
get complexed resulting in sharp change from wine red to blue which indicates
end-point of the titration.
Ca2+
+
EDTA 4-
CaEDTA 2-
Mg2+
+
EDTA 4-
MgEDTA 2-
Glassware/Apparatus required:
250 mL conical flask (1 no.)
12
50 mL burette (1 no.)
Measuring cylinder (100 mL) (1 no.)
20 mL pipette (1 no.)
Funnel (1 no,) and filter paper
Chemicals/Solvents required:
Standard ZnSO4 solution (20 mL each time)
Na2EDTA (~100 mL)
Buffer solution (pH = 10) (2 mL)
Eriochrome Black-T indicator (EBT)
Procedure:
Part I: Standardization of EDTA
Take exactly 20.0 mL of standard ZnSO4 solution provided into a clean 250
mL conical flask. Add 5 mL of buffer (pH 10) and 2-3 drops of EBT indicator
which turns the solution to wine-red colour. Titrate the standard ZnSO4 solution
with EDTA, the colour change from wine-red to blue is noted as the end point.
The titrations are repeated at least two times to get the concordant values. The
molarity of EDTA solution is calculated from the formula;
N1V1 = N2V2
Where N and V refer to normality and volume, respectively.
Part II: Total Hardness: Temporary Hardness + Permanent Hardness
Pipette out 20 mL of the given water sample into a clean conical flask, add 5
mL of the buffer solution (pH 10) and 2-3 drops of EBT indicator. Titrate the
wine-red solution against EDTA solution taken in a burette, till the contents of
the conical flask turn to blue colour without any reddish tinge. Note down the
volume of EDTA used. Repeat the titrations atleast two times to get concordant
results. Let the volume of EDTA used be V1 mL. The total hardness in terms of
an equivalent amount of CaCO3 is calculated using the following relation:
13
1 mL of 0.01 M EDTA = 1.00 mg of CaCO3
 Boil the remaining water sample on a hot plate for 15 min, cool it to room
temperature and filter it.
Part III: Permanent Hardness
Take 20.0 mL of the water from boiled, cooled and filtered sample using
pipette into a 250 mL conical flask. Add 5 mL of buffer solution (pH 10) and then
add 2-3 drops of EBT till the solution assumes a wine-red colour. Titrate this
solution against EDTA till the solution in the conical flask changes to blue colour.
Repeat for concordant titre values (V2 mL). From the titre value, the molarity of
the sample and hence the amount of CaCO3 in mg/litre can be calculated. This
gives the value of permanent hardness.
14
Experiment: 5
SELECTIVE EXTRACTION: Extraction of Caffeine
from Tea Leaves
Aim:
To extract the alkaloid natural product caffeine from tea leaves via acid-base
liquid-liquid solvent extraction techniques.
Principle:
The technique used to separate an organic compound selectively from a
mixture of compounds is called Selective extraction. Extraction process
selectively dissolves one or more compounds of the mixture into a suitable
solvent. The solution of these dissolved compounds is referred to as the Extract.
Here the organic solvent dichloromethane is used to extract caffeine from an
aqueous extract of tea leaves because caffeine is more
soluble in dichloromethane (140 mg/ml) than it is in
water (22 mg/ml). However, the tannins that are
slightly soluble in dichloromethane can be eliminated
by converting it to their salts (phenolic anions by
adding sodium carbonate) (tannins are phenolic
compounds of high molecular weight and being acidic
in nature can be converted to salts by deprotonation of the -OH group) which
remain in the water.
Caffeine, 1,3,7 - trimethylxanthine, belongs to a wide class of compounds
known as alkaloids. These are plant derived compounds with complex structure
containing nitrogen, and usually have roles in physiological activity. The melting
point of Caffeine is 238°C.
15
Glassware/Apparatus required:
Stoppered bottle (100 mL, 1 no.)
Büchner funnel (1 no.)
Separating funnel (100 mL, 1 no.)
Beaker (100 mL, 50 mL, 1 no. each)
Watch glass (1 or 2 no.)
Glass rod (1 no.)
Measuring Cylinder (10 ml, 25 mL, 1 no. each)
Sintered crucible (1 no.)
Crushed ice and Filter paper
Chemicals/Solvents required:
(Note: use only preparative balance)
Sodium hydroxide solution (0.2 N)
Tea leaves or powder (5 g)
Isopropanol (1 mL)
Dichloromethane (30 mL)
Anhydrous sodium sulphate LR grade (5 g)
n-Hexane LR grade (5 mL)
Procedure:
1. Weigh about 5.0 g of tea powder and take it in a 100 mL stoppered reagent
bottle.
2. Add 25 mL of dichloromethane solvent and 5 mL of 0.2 N NaOH solution
followed by 5 mL of water. Stir the contents gently for 7 to 10 minutes
[vigorous shaking may lead to formation of emulsion which should be
avoided].
3. Keep aside the bottle undisturbed for about 10 minutes.
4. Filter the contents carefully over a Büchner funnel having filter paper by using
16
aspirator suction.
5. Wash the contents with small amounts (<5 mL each time) of dichloromethane
(2-3 times) for good extraction. Transfer the organic layer to a separating
funnel (100 mL) and allow the contents undisturbed for few minutes.
6. Run down the clear organic layer into a clean and dry beaker (100 mL), add
three spatula of anhyd. sodium sulphate, keep aside for about 5 minutes.
7. Filter the contents carefully over a Büchner funnel having filter paper and
using aspirator suction. Transfer the organic layer to a dry beaker (50 mL) and
keep the beaker covered with a watch glass on a hot plate till one gets a dry
green powder (crude caffeine). [Organic solvent evaporation must be done
carefully]
8. The crude product was then dissolved in a minimum amount of isopropanol
using gentle heat when necessary (taken in a 25 mL conical flask).
9. Once a green coloured solution is obtained, allow it for natural cooling to RT
and then add 5 mL of hexane and cool it in ice.
10.White crystalline caffeine powder is obtained which is filtered in sintered
crucible and dried.
11.Both yield and melting point of the product are determined and reported.
17
Experiment: 6
COLORIMETRIC ESTIMATION: Estimation of Copper
in Brass Alloy by Colorimetric Method
Aim:
To estimate the amount of copper present in brass alloy by using colorimetric
method.
Principle:
The Beer-Lambert law (or Beer's law), the fundamental working principle
behind colorimetric estimation, suggests a linear relationship between absorbance
and concentration of an absorbing species. Brass is an alloy of copper and zinc.
The mass percentage of copper in brass can be determined colorimetrically by
utilizing the fact that the reaction of brass with concentrated nitric acid results in
a solution containing pale blue copper(II) nitrate and colourless zinc(II) nitrate.
Copper metal reacts readily with oxidizing agents such as concentrated nitric
acid and oxidizes to the copper(II) ion.
Cu(s) + 5HNO3(aq) → Cu(NO3)2(aq) + 3NO2(g) + 3H2O(l)
As products of this reaction, a water-soluble copper(II) nitrate produces a pale
blue solution, and a dense, toxic, redish brown nitrogen dioxide (NO2), gas are
formed. Furthermore, the solution of copper(II) nitrate on reaction with ammonia
solution forms tetramine copper(II) complex which is dark blue in colour and
responsible for colometric estimation.
Glassware/Apparatus required:
100 mL Conical flask (one per student)
Spatula
Distilled water bottle
Measuring Cylinders 10 mL
19
Small funnel
50 mL Standard flask
25 mL Standard flask (seven)
5 mL pipette (one)
Graduated pipette - 1, 2, 3 mL
Colorimeter with 610 nm filter
Chemicals/Solvents required:
(Note: use only analytical balance)
Brass alloy (0.12 g)
1:1 Nitric acid (10 mL)
Distilled Water (10 mL)
Urea (pinch)
1:1 Ammonia solution (35 mL)
Stock solution of Copper sulphate (5000 ppm) [15 to 20 mL of this solution
per student]
Procedure:
Part I:
1. Weigh accurately about 0.12 g of brass and transfer it into a 100 mL conical
flask.
2. Add to this 10 ml (measuring cylinder) of 1:1 nitric acid and boil gently for
10 minutes over flame (or hot plate) inside the fume hood until the evolution
of a reddish brown gas stops completely.
3. Then add 10 ml water and one gram (one spatula/pinch of compound) urea
and boil for a few minutes.
4. Cool the resultant solution to room temperature and transfer it quantitatively
into a 50 ml standard flask and make up to the mark.
5. Pipette out 5 ml of this solution into a 25 ml standard flask containing 5 ml
of 1:1 ammonia solution. The solution is mixed well and made up to 25 ml
20
mark.
6. Measure the absorbance of this solution using the instrument Colorimeter
equipped with 610 nm filter.
Part II:
1. From the stock solution of copper sulphate (5000 ppm) provided, pipette out
1, 2, 3, 4 and 5 ml of this solution into five different 25 ml standard flasks
containing 5 ml of 1:1 ammonia solution in each of them and make upto the
mark carefully.
2. Shake each of them carefully to ensure the solution in it is uniform in
concentration.
3. Also, prepare a blank solution (all as above but without CuSO4 solution) in
the same way.
4. Measure the absorbance of each of this solution at 610 nm filter the same
way.
5. Tabulate the readings, plot a graph and determine the copper content in brass
using the graph.
21
Experiment: 7
CONDUCTIVITY: Acid Strength of Citrus Fruit Juice by
Conductometer
Aim:
To determine the strength of an acid present in a given citrus fruit juice by
conductometry.
Principle:
Citrus fruits contain fairly a large amount of citric acid. A simple acid-base
titration with a strong base can be used to determine the acid strength. However,
some citrus fruits are colored and in such cases conventional volumetric titration
using a suitable dye indicator is not possible and therefore, different titration
techniques (such as conductometric, pH metric or spectrophotometric methods)
can be employed instead.
The present experiment is aimed at introducing two instruments for carrying
out acid-base titrations: a pH meter and a conductivity bridge. First part of the
experiment involves the use of pH meter for titration of a strong acid with a strong
base of unknown strength. A pH meter is a potentiometer, which uses a glass
electrode sensitive to H+ ion concentration. If a strong acid is titrated against a
strong base (in the burette), the pH of the solution varies as a sigmoidal curve
with a very sharp increase of pH at the end point.
Second part of the experiment is the conductometric titration of the citrus fruit
juice, (which, in all likely hood, is supplied to you after dilution in water), with a
standard sodium hydroxide solution (standardized in the first part of the
experiment). A solution containing ions conduct electricity due to movement of
ions to oppositely charged electrodes under the influence of an electric field.
More the concentration of free ions in a solution, more the conductance.
23
The conductance of a weak acid is usually low, as free ions furnished in the
solution is less. On titrating with a strong hydroxide solution (fully ionized), an
initial decrease of conductivity is observed due to mutual suppression of
ionization of the acid and the salt that is formed. However, after a few drops of
titrant addition, the less ionizable acid is progressively replaced by its completely
ionisable sodium salt, the conductance starts to increase linearly.
Once the end point is reached and all the acid has been converted to its salt,
addition of further sodium hydroxide results in a much rapid increase in the
conductance as OH ion conducts more than the acid anion. The end point is thus
the point where this change in slope takes place.
Glassware/Apparatus required:
Measuring cylinder (25 mL)
20 mL pipette (1 No’s)
50 mL burette (1 No’s)
250 mL conical flask (1 No’s)
Conductivity meter
100 mL beaker (2 No’s)
250 mL beaker (1 No’s)
Distilled water bottle
Chemicals/Solvents required:
0.1 N HCl solution (approx. 60.0 – 80.0 mL)
Sodium hydroxide (100 mL)
Procedure:
Part I: Standardization of the Sodium hydroxide solution
Pipette out exactly 20.0 mL of 0.1 N HCl using a handy pipette (don’t pipette
with mouth) and transfer it into a 250 mL conical flask. Add a drop of
phenolphthalein indicator to it. In a 50 mL burette, take sodium hydroxide
24
solution of unknown concentration. Titrate the HCl using NaOH until the solution
turns into pale pink. Carefully note the burette reading at the end-point. Repeat
the titrations until concordant values are obtained. Calculate the concentration of
the given NaOH solution.
Part-II: Determination for strength of the citrus fruit juice
Switch on the conductivity bridge and allow it to stabilize for 10 minutes.
Take the given juice solution (exactly 25 mL) in a 100 mL beaker and note its
conductance read by the instrument. Titrate with standard NaOH solution with
small addition (0.2 mL at a time). Note the burette readings and the corresponding
conductance after each addition. At the end point you will observe a faster
increase of conductance with NaOH addition. Stop the titration after 8/10
readings after the end point. Plot conductance vs. volume of base added. Identify
the equivalence point and estimate the strength of the juice solution given.
25
Experiment: 8
REACTION KINETICS: Ester Hydrolysis
Aim:
To determine the order and the rate constant for the acid catalyzed hydrolysis
of an ester at room temperature.
Principle:
In presence of acid, an ester (e.g., methyl acetate) hydrolyzes at a measurable rate
yielding alcohol (methyl alcohol) and carboxylic acid (acetic acid).
CH3COOCH3 + H2O ⎯⎯⎯⎯⎯⎯ CH3COOH + CH3OH
←
Assuming that the rate of this reaction is proportional to the concentration of the
ester and the water, the rate expression becomes:
Rate = k[Ester][H2O]
The reaction is performed in presence of excess water. Thus, change in its
concentration is negligible and [H2O] can be considered as constant. Moreover,
HCl catalyzes the reaction and hence, there is no change in its concentration.
Therefore, the overall rate depends only on the ester concentration and follows a
pseudo first order kinetics.
Rate = kpseudo[Ester]
where kpseudo = k[H2O]
The first-order rate constant can be expressed as:
k =
.
log
[
]
[
]
Where [Ester]0 is the initial concentration of the ester and [Ester]t is the
concentration of ester at time ‘t’. A straight-line between log
[
]
[
]
and t
essentially infers that the reaction follows a first-order kinetics and the rate
27
constant (k) can be obtained from the slope.
Glasswares/Apparatus required:
Stoppered bottle (250 mL, 1 no.)
Pipettes (10 mL, 5 mL, 2 mL, 1 no.)
Room Temperature and 80 oC Thermostats
Conical flask (250 mL, 2 no.)
Burette (50 mL, 1 no.)
Measuring cylinder (100 mL, 1 no.)
Stopwatch
Crushed ice
Chemicals/Solvents required:
Conc. Hydrochloric acid
Distilled Water
Methylacetate (5.0 mL)
Phenolphthalein indicator
Sodium hydroxide (0.2 N)
Procedure:
Ester concentration at different times are measured by back titrating the
carboxylic acid formed from the hydrolysis reaction. This is accomplised by
titrating the reaction mixture at different time intervals (t) using a standardized
NaOH solution. The rate constant can be expressed in terms of the volume of base
consumed (Vt) at time t and is given by the following equation:
k=
.
log
[
]
[
]
V∞-V0 corresponds to initial ester concentration and V∞-Vt corresponds to ester
concentration at time ’t’, respectively.
Measuement of V0 and Vt:
Take ~100 mL of 0.5 N HCl into a 250 mL stoppered bottle. Keep the bottle in a
28
trough of water at room temperature (thermostat) for about 10 minutes. Add ~5.0
mL of methyl acetate to this bottle using a pipette. Shake the bottle to ensure
thorough mixing. Start the stop watch as soon as ester is added. Immediately
withdraw exactly 5.0 mL of this reaction mixture using a pipette and add it to ~20
mL of ice cold distilled water already taken in a 200 mL conical flask. Add one
or two drops of phenolphthalein indicator and titrate against standardized NaOH
solution (0.2 N) taken in the burette. Note the end point color change. Note down
the titre value (Vt) at regular time intervals (t), for example; t = 0, 10, 20, 30, 40
and 50 minutes.
Measurement of V∞:
Keep the stoppered bottle in a trough of water at 80 oC for about 15 minutes. This
enables entire ester to hydrolyze yielding an equivalent quantity of acetic acid.
[CAUTION: Hold the stopper tight while the bottle is being heated to avoid
popping of stopper]. Bring it to room temperature and withdraw exactly 5 mL of
the reaction mixture with a pipette, transfer it into conical flask, add
phenolphthalein indicator. Titrate and note down the titre value, V∞.
29