1st semester chemistry lab manual (nep)

includes titrations and organic preparations

1. DEPARTMENT OF CHEMISTRY

A MANUAL FOR

I SEMESTER I YEAR B.5c STUDENTS
PRESCRIBED BY
DAVANGERE UNIVERSITY

NEP (2021-22)

2. 1 B.Sc. | Semester Chemistry Lab Manual E

CHEMISTRY LAB: CHM P -1
PART-A: Analytical Chemistry
1. Calibration of glassware: pipette, burette and volumetric flask.
2. Determination of alkali present in soaps/detergents
3. Determination of alkali content in antacids
4. Determination of iron (Il) using potassium dichromate
5, Determination of oxalic acid using potassium permanganate solution
6, Standardization of EDTA solution and determination of hardness of water
PART-B: Organic Chemistry
1. Selection of suitable solvents for Purification /Crystallization of organic compounds.
2, Preparation of acetanilide from aniline using Zn/acetic acid (green method).
3. Synthesis of p-nitro acetanilide from acetanilide using nitrating mixture.
4. Bromination of acetanilide
(i) conventional method and/or
(Gi) with ceric ammonium nitrate and potassium bromide (green method).
5. Hydrolysis of methyl m-nitrobenzoate to m-nitrobenzoic acid (conventional method)

6. Synthesis of diazoaminobenzene from aniline (conventional method).

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3. 1 B.Sc. | Semester Chemistry Lab Manual

Experiment No. 1: Calibration of Pipette, Burette and Standard flask
Aim: To calibrate the given pipette, burette and standard flask.

Principle: It is necessary that all volumetric glassware like pipette, burette, volumetric flask,
ete. should be tested for accuracy before use. This is done in order to find error of graduation,
ifany.
Pipette having mark is employed to measure a fixed volume of liquid. It is called transfer
pipette. The volume of water delivered by the pipette is weighed by knowing the density of
water at laboratory temperature the exact volume of water is calculated. This gives the true

capacity ofthe pipette.

Procedure:

Part A: Calibration of pipette: The pipette is first cleaned with chromic acid. It is then

thoroughly washed with tap water and rinsed with distilled water.

‘A clean and dry 100 cm? beaker is weighed accurately. The pipette is filled with the distilled
water (stored at lab temperature) well above the mark. The outer surface of the pipette is
dried by means of an ordinary filter paper. Water is run out until the lower meniscus is
adjusted to the mark. Its then transferred into a previously weighed beaker. The beaker is
‘weighed again. The laboratory temperature is noted. The exact volume of water delivered by
the pipette is calculated, This gives the true capacity of the pipette.

Part B: Calibration of the burette: The burette is washed and rinsed with distilled water. It
then filled with distilled water up to the tip without any air bubble. The lower meniscus is
adjusted to zero. Now 10 cm? of water is run down from the burette into a previously weighed
beaker. The beaker is weighed again. Another 10 cm? of water (from 10.0 cm to 20.0 em) is
added to the same beaker and weighed again. The same procedure is repeated up to 50.0 cm’.

Part C: Calibration of standard flask: A clean and dry 100 cm? standard flask is weighed
accurately, The standard flask is filled with the distilled water (stored at lab temperature)
exactly up to the mark. It is weighed accurately. The laboratory temperature is noted. The
‘exact capacity of the standard flask is calculated. This gives the true capacity of the standard

flask.

Result: The true capacity of the pipette
‘The true capacity of the burette: 1) (0 - 10 cm)
2) (10 - 20cm) =
3) (20-30 em)
4) (30-40 cm)
5) (40-50 cm)

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4. 1B.Sc. 1 Semester Chemistry Lab Manual

Observations & Calculations:
Part A: Calibration of pipette:
1. Laboratory temperatu

e
2. Density of water at the laboratory temperature

=
[ | 7 ‘Observed volume
acted | ace PA wage | ri
| Sapacity | ight of beaker of ‘True capacity Correction
| ofthe beaker! + water water of the pipette
Pipette | view
vas | m Lee | mm | Oe") mer
| is | ® Density of water
a
|
Homes
ne a
a lb er mero
Burette | Volume Mass
[; En Observed
"Marked | "of | beake | massof | YM cor
fi ecte y LS
inem || water | _ vom
v wi | w | (we-wi) ww) | cv
h | Densityofwater cms
| 100
[2201 s00| 100 |
Ps mas | | |
(a lue) mag |] PA
le lol aol am |
| |
ll

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5. 1 BSc.1 Semester Chemistry Lab Manual

Part ¢: Calibration of standard flask:
1. Laboratory temperature... €

2 Density ofwater at che laboratory temperature = un em
Pen a observed volume
capacity | Weight of on Weight | 7, d
ofthe | standard | Sanda of True capacity, | correction
standard) flask BERN water (atthe standard,
aula water flask
| | Vem _
(we = wi)
vim | w av |
CR a
|
100m |
|
DEPARTMENT OF CHEMISTRY Page 413

6. 1 B.Sc. 1 Semester Chemistry Lab Manual RZ
A A
Experiment No. 2: Determination of alkali present in soaps/detergents.

‘Aim: To determine the percentage of free alka in the soap sample.
Apparatus: - Burette, beaker, conical Mask; titration lask, measuring cylinder, funnel.

Chemicals:
*Soap sample
“Water
“001 N Hol
* Phenolphthalein indicator

Procedure: -

+ Weigh out 10g of foundry soap and transfer itinto a beaker containing 150 ml of
distilled water.

‘+ Warm the beaker to dissolve soap for 30 to 40 minutes and transfer this solution along,
with the washings to the 250 ml standard flask.

+ Add more distilled water to make up to the mark.

+ Don't shake the flask otherwise foam will be produced which may give wrong results.

+ Take 10 ml of the soap solution in the titration flask.

‘+ Add two drops of phenolphthalein indicator in the titration flask, color will change into
pink.

‘+ Titrate it against 0.01N HC from the burette, until the solution turn colorless.

‘+ Repeat the process two or three times to get concordant results

RESULT:
‘The percentage of alkall in soap is.

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7. 1 BSc. | Semester Chemistry Lab Manual

Observation and calculations:
Determination of alkall in soap solution:
In burette: HCI Solution

In conical flask: Soap solution

Indicator: Phenolphthalein

End point: pink to colorless

SLNO Initial burette | Final burette reading | Volume of hydrochloric
reading acid used (in ml)

(MV) = (MV) Sur
M = (MY) a / Vin

‘Amount of NaOH in g/L= M4

Amount of NaOH in g/L= Xg/L

‘Amount in g in 1000 ml of sample= xg.

‘Amount in gin 1 ml of sample= X/1000

Amount in g in 250 ml of sample= Xx250/1000 =Yg

Percentage Alkalinity=Yx100/10=.

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8. 1 BSc. I Semester Chemistry Lab Manual

Experiment No, 3: Determination of alkali content in antacid tablets using HCI

‘Aim: To determine the alkali content in an antacid tablet using HCI

Chemicals required: antacid tablets, sodium carbonate (0.1N), and, hydrochloric acid solution
(O.1N) methyl orange, distilled water.

ettes (10 mi), burette, beaker, pestle and

flask (100 ml),

Apparatus required: volumet
mortar, filter stand

‘Theory: Antacids, which are mildly alkaline substances like sodium carbonate, are prescribed
to neutralize stomach acidity. The strength of alkali content in an antacid is estimated by
titrating itagainst HCl in the presence of methyl orange indicator.

Procedure:
Part A: Preparation of Standard solution of sodium carbonate (0.1N): Weigh accurately
053 grams of AR grade sodium carbonate and transfer it into a 100 ml measuring flask with
the help of distilled water, Add more distilled water, stopper the flask and shake thoroughly so
that the alkali completely dissolves. Make up the volume by adding more distilled water.

Part B: Standardization of hydrochloric acid: Fill the clean dry burette with hydrochloric
acid solution. Pipette out 10 ml of sodium carbonate solution into a 250 ml conical flask and
add 2-3 drops of methyl orange indicator. Titrate this solution with the hydrochloric acid
solution with constant stirring until the solution in conical flask acquires a very faint yellow
color. Continue the addition of acid drop wise with stirring until the color of solution becomes
orange red color. This is the end point. Repeat the process two or three times in order to
obtain concordant results.

Part C: Determination of alkali content in an antacid tablet: Weigh accurately about 4
grams of well powered antacid tablet and transfer it into a 250 ml measuring flask. Add about
50-100 ml of distilled water, stopper the flask and shake thoroughly so that the antacid
completely dissolves. Make up the volume up to 250 ml mark by adding more distilled water.
Pipette out 10 ml of antacid solution into a 100 ml conical flask and add 2-3 drops of methyl
orange indicator, The solution turns yellow. Titrate this solution with standardized HC tll the
solution acquires orange red color. Repeat the whole process to take at least two similar
readings.

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DEPARTMENT OF CHEMISTRY

9. 1 B.Sc. 1 Semester Chemistry Lab Manual

Observations and calculations:
‘Weight of empty weighing bottle = W=
‘Weight of weighing bottle + sodium carbonate = W;
Weight of sodium carbonate = W = Wa - Wr
Normality of sodium carbonate (Eq, We

‘Standardization of HCl solution:

In burette: HCI Solution

In conical flask: sodium carbonate solution
Indicator: Methyl orange

End point: Yellow to orange red

SLNO | Inkialburete | Finalburete reading | Volume of hydrochloric
| reading acid used (in ml)

1

EE

‘The Concordant burette reading =

mi
(NAV) = (NX) sos

Na = (09) waco / Vue

Determination of alkali content in an antacid tablet
In burette: HCI Solution.

In conical flask: Antacid solution

Indicator: Methyl orange

End point: Yellow to orange red

SLNO | Initial burette reading | Final burette reading | Volume of standardized
hydrochloric acid used (in
mi)

‘The Concordant burette reading

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10. 1B.Sc. Semester Chemistry Lab Manual

(Nx Vianos = (N XV) ne

Nuor= (NV) vo Atco =

Amount of NaHCO present in one liter of antacid solution

= Nnatoas x Equivalent weight of NaHCO»
= Nano x 84

=xg

AmountofNaHCOs presentin 250 ml ofantacidsolution =x/4 g=Y8

This is the amount of NaHCOs present in 4 grams of antacid tablet.

.. of NalICOs presentin antacid = yx 100,/4

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11. 1 BSc. Semester Chemistry Lab Manual

Experiment No. 4: Determination of Iron (I) using potassium dichromate

Aim: To determine the amount of fertic chloride present in a liter of the solution using
approximately 0.1 N potassium dichromate solution and Ferrous Ammonium Sulphate (Mohr

sal) crystals.

Principle: In presence of dilute sulphuric acid, potassium dichromate serves as an oxidizing

agent
KaCraO> + 42506 —» KaSO4 + Cra(SO4)o + 41120 + 310]

‘The ferrous ions are oxidized by dichromate to ferric ions.
2FeSO4 + HiSO4+ [0] ——+Fe2 S04)» + Ha

Potassium dichromate solution can be standardized using standard solution of ferrous
ammonium sulphate (Mohr salt). A known volume of the ferrous ammonium sulphate
solution is titrated in presence of sulphuric acid against standard potassium dichromate
solution. The orange-colored potassium dichromate is changed to green colored chromic salt
due to reduction. Diphenylamine is used as the internal indicator. Its oxidized by dichromate
to a violetcolored substance after the complete oxidation of ferrous ions present in the
solution, Thus, the appearance of violet color marks the end point of he titration,

À known volume of ferric chloride solution is taken. The ferric ions present in the solution
are reduced to ferrous ions using stannous chloride in presence of hydrochloric acid in hot
condition

2Fe™ + Sn? —e 2 et + Sn

‘The excess of stannous chloride is removed by the addition of mercuric chloride. Then, the
amount of ron present in the solution is determined by titrating against potassium dichromate
solution using diphenylamine as an interna indicator.

Procedure: Part A: Preparation of standard Mohr' salt solution

‘The weighing bottle containing FAS crystals is weighed accurately. The crystals are carefully
transferred into a 250 cm’ standard flask using a funnel. The crystals are dissolved by adding
small amount of distilled water. 5 cm? of dilute sulphuric acid is added to it. The solution is
made up to the mark using distilled water and shaken well for uniform concentration. The
empty weighing bottle is weighed again. The difference of the two masses gives the mass of
FAS crystals. The normality of FAS solution is calculated,

Part B: Standardization of potassium dichromate:
10 cm? of standard FAS solution is pipetted out into a clean conical flask. 1 test tube of

dilute sulphuric acid - phosphoric acid mixture and 2 drops of diphenylamine indicator are

added to it. The solution is titrated against potassium dichromate solution taken in the burette

until the green color first formed just changes to violet color, The titration is repeated for

concordant ttre values,

DEPARTMENT OF CHEMISTRY

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1 BSc. Semester Chemistry Lab Manual @

Part C: Determination of amount of ferric chloride:

10 em? of the given ferric chloride solution is pipette out into a clean conical ask. 2 cm’ of
cone. HCI is added and the solution is heated nearly to boiling, Stannous chloride solution is
added to the hot solution from a burette drop wise until yellow color of the solution is
discharged. 2 drops of stannous chloride are added in excess. The contents of the flask are
cooled to room temperature under running tap water. 5 cm of saturated solution of mercuric
chloride is added to get a silky white precipitate, (The solution has to be discarded if no
precipitate or grey precipitate is obtained. In that case, the reduction process has to be
repeated). 1 test tube of dilute sulphuric acid - phosphoric acid mixture and 1-2 drops of
diphenylamine indicator are added to it This solution is titrated against potassium
dichromate solution until the green color formed just changes to violet color. The titration is
‘repeated to get concordant ttre values.

Result: Mass of ferric chloride per iter of solution =... g
Observation and Calculations:

Part A: Preparation of standard ferrous ammonium sulphate solution:
Mass of weighing bottle +FAS crystals WE

Mass of empty weighing bottle we

Mass of FAS crystals dissolved (WW) = ont

Normality of FAS solution = Hass 21 PAS crystals per250en x 4

a eqmassof FAS

cree ee
sr

Part B: Standardization of potassium dichromate solution:
Titration — :K2Cra07 solution vs FAS solution

Burette _ : Potassium dichromate solution

Conical flask: 10 cm? of standard FAS solution + 14.1. of H:SOx~HaPO4 mixture
Indicator: 2 drops of diphenylamine

Endpoint — : Green to violet

Final burette |
reading
Initial bureite
reading |
Volume of KGrz07
added in em? (TV)

DEPARTMENT OF CHEMISTRY age 11132

13. 1 BSc. 1 Semester Chemistry Lab Manual

Xeno, = (N X Vas

Mano, = LD = x0
Visor

Part C: Determination of amount of ferric chloride
Titration :K:Cr207 solution vs ferric chloride solution

Burette Standard K:CrOrsolution

Conical Mask: 10 em of ferrie chloride soln. + 2em? ofcone. HCL + SnClasoln.+
HgCl son. + 1 & of phosphoric acid - sulphuric acid mixture

Indicator :2drops of diphenylamine

End Point — ¿Green t violet

Trial No. 1 i

Final burette
reading
Initial burette |
reading,

Volume of KaGra07 |
added in cm (Tv) |

WM) pect, = (NV),

Mass of FeCls/ lite ofthe solution = Mac, > g eq. mass of FeCls

= x 16235 8.

8

rei XO ea we o ects

Mass ofFeCh/250 cm of the solution = a

DEPARTMENT OF CHEMISTRY Page 12132

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1 BSc. 1 Semester Chemistry Lab Manual @

Experiment No. 5: Determination of Oxalic acid using KMnO4 solution.

Aim: To determine the amount of oxalic acid present in 250 cm of the given solution using
potassium permanganate solution

Procedure: Potassium permanganate is an oxidizing agent and oxalic acd isa reducing agent.
Potassium permanganate oxidizes oxalic acid to carbon dioxide and water in acid medium
under hot conditions. In this process, potassium permanganate is reduced to colorless
manganous sulphate. Therefore, at the end point, the solution turns pink. It is a titration
involving an oxidizing agent and a reducing agent. Hence, it is called a redox titration, The
titration does not need any indicator as potassium permanganate produces a permanent pink
color at the end point, In the beginning, the titration is carried out by adding potassium
Permanganate solution dropwise as the reaction is catalyzed by Mn?* ions. Once the Mn ions
are formed, the titration can be carried out by adding potassium permanganate solution one
ml ata time. (Ifthe titration is carried out by adding potassium permanganate one or two ml at
a time in the beginning, a brown solution is obtained. In such a situation, the solution is
discarded and a fresh trial is carried out).

In the first part of titration, Mohr’s salt solution is titrated against potassium permanganate
solution. Potassium permanganate oxidizes ferrous ions present in the Mohr' salt solution to

ferric ions in presence of sulphuric acid,

Reactions:
2KMnO4 + 3 H:S0¢ ——* K:SO4 + 2 MnSO4 + 3120 + 5 [0]

[2 FeSOs + H2504 + [0] —+Fe:(S0)s + 120] x 5

ZKMnO4 + 8 H:S04 + 10 FeSO, ——» FeaiS0s)s + K2S0s + 2MnS0s + 810

In the second part of titration, hot oxalic acid solution is titrated against potassium
permanganate solution. Potassium permanganate oxidizes oxalic acid in presence of sulphurie
acid.

Reactions:

5(COOH); + 2Mn0,-+ 6H > 10C0:f + 2Mn + 8H.0

Procedure:
Part A: Preparation of Standard solution of Mohr's salt (Ferrous ammonium sulphate):

A weighing bottle containing about 98 g of Mohr's salt is weighed accurately. The crystals,
are transferred into a clean 250 cm? standard flask and are dissolved by adding small amount

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HEMISTRY Pa

15. 1 Semester Chemistry Lab Manual

of distilled water. The solution is made up to the mark using distilled water and shaken well
for uniform concentration. The empty weighing bottle is weighed again. The difference of the
‘wo masses gives the mass of Mohr's salt. The normality of oxalic acid solution is calculated

Part B: Standardization of potassium permanganate solution:

10 cm? of standard FAS solution is pipetted into a clean conical flask. One test tube full of
dilute sulphuric acid and 2 test tube full of water are added. The solution is titrated against
Potassium permanganate solution taken in the burette until the colorless solution just changes
to pale pink. The titration is repeated for concordant ttrevalues.

Part C: Determination of amount of oxalic acid in given solution:

10 cm? of oxalic acid solution is pipetted into a clean conical flask. One test tube full of dilute
sulphuric acid is added to it. The solution is heated nearly to boiling (the solution should not be
boiled). The hot solution is titrated against potassium permanganate solution taken in the
burette until the colorless solution just changes to pale pink (Initially add KMnO4 solution
slowly). The titration is repeated for concordant titrevalues,

Result: Mass of oxalic acid present in 250 cm? ofthe solutior
Observations and Calculations:

Part A: Preparation of standard FAS solution:

Mass of weighing bottle + FAS crystals Dors
Mass of empty weighing bottle Mess
Mass of FAS erystals dissolved CASE"

(Mass of oxalic acid crystals per 250 em’
Den. mass of F

Normality of FAS solution

x4
3921

Part B: Standardization of potassium permanganate solution:

Titration: FAS vs KMnOs
Burette otassium permanganate solution

Conical flask: 10 cm? of standard FAS solution + 1 t of dil H:SO4
Indicator _ :Selfindicator (KMnO itself)

End point — Colorless to pale pink

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[rial No. 1 u T ui
Final burette
reading
Initial buretie
reading _ _
Volume ofKMnO+
added in cm

(N XV)xmno, = (N X Voxaticacia

Vas x10
Vaso

Nxsnos

Part €: Estimation of oxalic acid:
Titration _:KMnOs vs Oxalicacid
Burette
Conical flask: 25 cm of oxalic acid solution + 1 € full of di. 12504 +Boil
Indicator :Selfindicator (KMnOs itself)

End Point

otassium permanganate solution

lorless to pale pink

Trial No. 1 T u m ]
Final burette
‘reading
Initial burette

ro

N X Voxaticacia = (N % Vamo,

U ico, x
= La.
Noxatic acid = Yo cic acia 10

Noxaicacia X 9 eg. mass of Oxalic acid
+

Mass of Oxalic acid /250 cm of the solution =

DEPARTMENT OF CHEMISTRY Page 15132

17. 1 BSc. 1 Semester Chemistry Lab Manual

Experiment No. 6: Standardization of EDTA solution and determination of hardness of

water

‘Aim: To estimate the total hardness of the given sample of water using appro}
EDTA solution and zine sulphate crystals,

ately 0.02 M

Principle: The total hardness of water is generally due to dissolved calcium and magnesium
salts. This may be determined by complexometrc titration with EDTA.

HOOC- HR CHaCOO- Nat
N-~CHe-CHa-N

Nat -00C - CH2 4 CH:COOH

EDTA, being a chelating agent, forms extremely stable complexes with calcium and
‘magnesium ions, which cause hardness.
Me + EDTA ——> (ME-EDTA] + In
blue
‘The dye, known as eriochrome black-T, serves as an excellent indicator. When a small
amount of indicator is added to hard water with a pH of about 10.0, it combines with a few of
the Ca?» and Mg2* ions to form a weak wine-red colored complex as shown below:

Mg" + In ——+ [Mg?-In)
blue _wine-red complex

During the titration with EDTA, all the free Ca and Mg? ions causing hardness are
complexed. Finally, EDTA disrupts the wine-red complex as it is capable of forming more
stable complexes with Ca* and Mg ions. This action liberates the eriochrome black-T
indicator and the wine-red color changes to. clear blue color, indicating the end of titration,

EDTA solution is standardized by titrating with standard solution of zinc sulphate using
eriochrome black-T indicator.

Procedure:
Part A: Preparation of standard solution of zine sulphate:

‘The weighing bottle containing ZnS04 crystals is weighed accurately. The crystals are
carefully transferred into a 250 cm’ standard flask. The crystals are dissolved by adding small
amount of distilled water. 5 em? of dilute sulphuric acid is added to it. The solution is made up
to the mark using distilled water and shaken well for uniform concentration, The empty
‘weighing bottle is weighed again. The difference of the two masses gives the mass of zinc
sulphate crystals. The normality of ine sulphate solution is calculated,

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18. 1 B.Sc. I Semester Chemistry Lab Manual
Part B: Standardization of EDTA solution:

10 cm’ of zine sulphate solution is pipette out into a clean conical flask. 5 cm? of NHs - NHCl
buffer and a pinch of solid eriochrome black-T indicator are added. ‘The wine-red colored
solution so obtained is titrated against standard EDTA solution taken in the burette until the
color of the solution just changes to clear blue. The titration is repeated for concordant titre
values.

Part C: Determination of total hardness of the given sample of water:
10 cm of the given sample of water is pipette into a clean conical flask. 5 cm? of NH - NICH
buffer and a pinch of solid eriochrome black-T indicator are added. The wine-red colored
solution so obtained is titrated against standard EDTA solution taken in the burette until the
color of the solution just changes to clear blue. The titration is repeated for concordant titre
values.

Result: Total hardness of given sample of water =. ppm of C2C0s.
Observation and Calculations:

Part A: Preparation of standard zinc sulphate solution:

Mass of weighing bottle + ZnSOsIystals Wi = soon

Mass of empty weighing bottle wre.

Mass of ZnSO, crystals dissolved [CPS ER"

(Mass of 21504 per 250 cm5) x 4
9 mol. mass of Zn504

Molarity ofZnSOs solution =

ww) x 4
28754

x4
28754

Part B: Standardization of EDTA solution:

Titration: EDTA solution vs zinc sulphate solution
Burette — :EDTAsolution

Conical flask: 10 cm of standard ZnS0 solution + 5 cm? of NH3 - NHC! buffer
Indicator _ : A pinch of eriochrome black-T

Endpoint: Wine red to clear blue

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19. 1B.Sc. | Semester Chemistry Lab Manual

ria
| Final burette
reading | |
Initial burette

(reading ___
Volume of EDTA
added in em? (TV) | |

(MX Wera = (M X V)zns0,

x10

Part C: Estimation of total hardness of water

Titration — : EDTA solution vs hard water

Burette Indard EDTA solution

Conical flask: 10 cmof hard water + 5 cm? of NHs - NHACl buffer
Indicator _ : A pinch of eriochrome black-T

End Point _:Wine ed toclearblue
Malle | 1 D à

Final burete

reading |
Ina rete

reading |
Volume of EDTA

added in cm? (TV)

Volume of …… M EDTA solution required for 50 cm? of given sample of hard water

Lem of 0.01 M EDT/

100 mg of CaCO

‘Therefore, 1 em? of M EDTÍ

mg of CaCO (Say 2)
‘Total hardness of the given sample of water (expressed in terms of number of parts of CaCOs

Tee oz

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20. 1 B.Sc. | Semester Chemistry Lab Manual

Part-B
ORGANIC CHEMISTRY

Experiment No: 1: SELECTION OF SUITABLE SOLVENTS FOR PURIFICATION /

CRYSTALLISATION OF ORGANIC COMPOUNDS

‘Types of Purification
A large number of methods are available forthe purification of substances. The choice of method,
however, depends upon the nature of substance (whether solid or liquid) also depends on the
type of impurities presentin it We commonly use these methods for purification of substances:

+ Simple crystallization

+ Fractional erystalization

+ Sublimation

+ Simple distillation

+ Fractional distillation

+ Distillation under reduced pressure

+ Steam distillation

+ Azeotropic distillation

+ Chromatography

‘Simple Crystallization
‘This is the most common method that we use to purify organic solids. For crystallisation, a
suitable solventis one
+ which dissolves more of the substance at a higher temperature than at room
‘temperature
+ in which impurities are either insoluble or dissolve to an extent that they remain in
solution (in the mother liquor) upon crystallization
‘+ which is not highly inflammable and
+ which does not react chemically with the compound to be crystallized. The most
commonly-used solvents for crystallization are water, alcohol, ether, chloroform,
carbon- tetrachloride, acetone, benzene, petroleum ether ete.

Fractional Crystallization
Itisthe process of separation of different components of a mixture by repeated crystallisations. In
the first step, we dissolve the mixture in a solvent in which the two components have different
solubilities. When we cool a hot saturated solution of this mixture, the less soluble component
crystallises out first while the more soluble substance remains in solution.

‘The mother liquor left after crystallisation of the less soluble component is again concentrated
and then we allow ito cool. Hence, we obtain the erystals ofthe more soluble component.
Sublimation

Certain organic solids on heating directly change from solid to vapour state without passing
through a liquid state. These substances are sublimable This process is sublimation.

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We use this process for the separation of sublimable volatile compounds from non-sublimable
impurities. We use this for the purposes of purification of camphor, naphthalene, anthracene,
benzoic acid, lodine and salicylic acid etc containing non-volatile impurities.

Simple Distillation

Distillation is the joint process of vaporization and condensation. We use this method for the
purification of liquids which boil without decomposition and contain non-volatile impurities. We
can also use this method for separating liquids having sufficient difference in ther boling points.

Dismuuen
QU

Fractional Distillation

We can use this process to separate a mixture of two or more miscible liquids which have boiling
points close to each other. We carry out this process by using fractionating columns. The
fractionating column isa special type of long glass tube that has obstructions tothe passage ofthe
vapour upwards and that of liquid downwards. This method can separate a mixture of acetone (b.
p.330 K) and methyl alcohol (b. p.338 K) or a mixture of benzene and toluene.

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22. 1 B.Sc. Semester Chemistry Lab Manual

‘Thermometer

To sink

Fractionating Copdenar
column with amor
packing ges
Lindo o 5 \
distiled Water inter

Distilled liquid

(The vapours of lower boiling fraction reach the tap of the column fist

followed by

vapours of higher boiling fractions à

Purification of Liquids - Fractional Distillation
Distillation under Reduced Pressure
We use this method for the purification of high boiling liquids and liquids which decompose at or

below their boiling points. Practical examples include the crude oil industry, sugarcane industry
ete,

Steam Distillation
‘This method is applicable for the separation and purification of those organic compounds (solids
or liquids) whieh:

+ are insoluble in water

+ are volatile in steam

+ possess a high vapor pressure (10-15 mm Hg) at 373 K and

+ contain non-volatile impurities

DEPARTMENT OF CHEMISTRY Page 21132

23. istry Lab Manual

PU condensed water
jw IN

compaurd 0
he did,

Purification of Liquids by Steam Distilation

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24. 1 BSc 1 Semester Chemistry Lab Manual

Experiment No.2: Preparation of Acetanilide from aniline using Zn/acetic acid (Green method)
‚Alm: Acetylation of primary amine (Preparation of acetanilide):

Theory: Acetyl derivatives of aromatic amines may be prepared citer by acetic anhydride, acctyl chloride
or acetic acid Primary amines react realy on warming with acetic anhydride to yield, in the frst instance
the monoacety] derivative. (If the heating is prolonged and excess of acctic anhydride is used, variable
‘amounts of diacetyl derivatives ae formed). The reaction of acetylation is witen as follows:

[ = 7

" o. pl |
On
EM ee" Bie

Conventional method: Non green solvent dichloromethane is used; Pyridine is tone and is not eco:
friendly. Acetic anhydride leaves one molecule of acetic acid unused which devoid the rule of atom
economy.

Non-green Components: Use of chlorinated solvent like CH:Ch, pyridine is also not eco-friendly and
acetic anhydride leaves one molecule of acetic acid unused (not atom-economic)

Greener approach:
+ A mixture of aniline and zinc dust in acetic acid in a round bottom flask was heated over a
gente flame using water condenser.
‘+ Heating was continued for about Z hrs

{The ci mito was then cael poured ia ld wate beater vith olga
+ Tiran cafe ere sprl sly
2 Aer mn e asado ae wre ee tatin
+ Th es ere wach er ie Buchner ni er an the products de
© Ras ee in bling water. mes, dolor cara hay u Ta
method des as ile ac any, hou sent los waste ce Sone
procedure eld be eid o wi stc aline fom, vs, met
pere
o
Nie md
DEPARTMENT OF CHEMIST aia

25. I B.Sc. | Semester Chemistry Lab Manual

Green Context: Avoids use of acetic anhydride (usage banned in some states, due to its utility in
narcotic business), minimizes waste by-products and avoids hazardous solvent.

Report: Yield ofthe crude sample = M =.
Melting point of the crystallized sample = 114°C

Calculation of theoretical yield:
1 gram molecular weight of Aniline = 1 gram molecular weight of Acetani

93g of aniline

35 gof acetanilide,

+X gofanilin gives 22

N gofacetanilide

‘Theoretical Vield (N) of Yield ==

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OF CHEMISTRY a

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26. 1 B.Sc. 1 Semester Chemistry Lab Manual

Experiment No: 3
Preparation of p-Nitro acetanilide from acetanilide

Aime

To prepare p-Nitro acetanilide from acetanilide and acetic acid in the presence ofnitrating mixture

Theory:

‘The organic compound p-nitro acetanilide is prepared from acetanilide through nitration, When

acetanilide is treated with nitrating mixture that is a mixture of nitric acid and sulphuric acid p-nitro

acetanilide is formed. Along with p-nitro acetanilide, o-nitro acetanilide Is also formed as a minor

Product. Since o-nitro acetanilide is very much soluble in alcohol it is very easy to isolate p-nitro

acetanilide through crystallization

“The chemical reactions involved in this process is given below.

NHCOCH, ICOCH, NHCOCH,
NO. 1450, 4 a
NO, gum

Itis an electrophilic substitution reaction. The electrophile -NO; will attach the para position because
the -NHCOCH, isan electron releasing group. Nitro aniline can be prepared by this type of reactions
because nitration of aniline is not possible, amino group gets oxidized with nitrating mixture. In order
to protect the amino group from oxidation acetanilide is frst nitrated to give p-nitro acetanilide and

‘then on hydrolysis to give p-nitroaniline which I dificult to obtain by direct nitration.

Other names - N-(4-nitrophenyl) acetamide, p-Acetamido nitrobenzene, p-Nitro acetanilide, N-Acetyl-
nitro:

Reagents Required: Acetaniide, Acetic acid, Concentrated Sulphuric acid, Puming Nitric acid, Ethyl
alcohol

Procedui
1. Take 1 gm of finely powdered acetanilide ina clean beaker and dissolve it by adding glacial
acetic acid by string the content carefully at room temperature,
2. Gently warm the mixture to dissolve acetanilide completely.
3. Cool the solution and add concentrated sulphuric acid slowly with constant tiring. The
solution becomes warm, keep the mixture in ice-bath and clear solution is obtained.
4. Tothe cool solution add fuming nitric acid dropwise through a dropping funnel with constant
stirring.
5. Maintain the temperature below 20°C during the whole process.
6. Once the addition of nitric acid is completed, the beaker is removed from the freezing mixture
bath and allow standing for half an hour at room temperature
7. Pour the mixture into 100gm of crushed ice in a beaker and stir well
Large erystals of p-nitro acetanilide is obtained, Filter the crystals through filter paper:
9. The separated p-nitro acetanilide is washed with cold water in order to remove excess of acid.

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10, [tis crystallized from ethyl alcohol. Dry the erystals in the folds of ter paper and weigh them
to know the yield

Report: Yield ofthe crude sample = M = 8
Melting point ofthe crystallized sample = 2149C

Calculation of theoretical yield:
4 gram molecular weight of Acetaniid
135g of Acetanlide = 180.164 ofp

1 gram molecular weight of p-Nitro acetanilide,
itroacetanilide.

19016xx
X of Acetanilide gives 12029 = y y of acetanilide
Theoretical Yield (N) Experimental Yield (M) ‘% of Yield |

Precautions:
1. Temperature should not exeeed more than 20°
2. Advisable to add nitric acid into the reaction mixture while its immersed in ie-bath
3. Add fuming nitric acid drop by drop carefully and do not inhale the fumes of nitric acid.

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28. 1 BSc. I Semester Chemistry Lab Manual

Experiment No.4 (0) Electrophilic aromatic substitution reaction-I (Bromination of
acetanilide).

‘Aim: To prepare p-Bromoacetanilide by bromination of acetanilide, a conventional method.
Theory: Acetanilide on bromination gives a mixture of ortho and para Bromo acetanilide (A difference rom
aniline which gives 2:46 trbromo aniline owing to the deactivating property of acetyl group). o-Bromo

nie being highly soluble in alcohol helps in the crysalizatin of pure p- Bromo acetanilide.

och, com
AS
ee: + Hor
serie Poromeacetaniise

Reagents:
+ Acetanilide: Se

+ Glacial acetic aci: ce
‘+ Bromine in acetic acid: 2 co

Procedure:
+ Dissolve Sg of acetanilide in 25 cc o gacialacei aid in 200 ml fas.
+ Now dissolve 2.1 ce of bromine in 30 ce of glacial acetic acid and add this solution drop wise, with

string into acetanilide solution in glacial acetic acid.
‘Allow the mixture to stand for half an hour and pour the contents to about 250 ce cold water

Fier and wash the product with water. Ciystalize from ethyl alcohol. Recrystaliz 1 g of p-brome
acetanilide from ethy alcohol

Report: Yield of the crude sample

‚sic

‘Melting point ofthe crystallized sample
Caleulation of theoretical yield:
1 gram molecular weight of Acetanilide =1 gram molecular weight of p-Bromo acetanilide.

1358 of acetanilide = 214g of p- Bromo acetanilide

X of Acide gives 22 = go p- Bromo acti

a | ann |
ihre | pene iu |

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29. E)
1 B.Sc. | Semester Chemistry Lab Manual RZ,

(i) Bromination of acetanilide with ceric ammonium nitrate and potassium bromide (green
method)
Reagents required:

+ Cericammonium nitrate
+ Kor
+ Ethanol
Green Procedure:
‘+ Inaconical flask acetanilide was dissolved in ethanol.
‘+ Then potassium bromide and ceric ammonium nitrate were dissolved in water.
‘+ This solution was transferred into an addition funnel,

This solution was added drop wise to the conical ask containing acetanilide solution.

After the addition was over, the reaction mixture was stirred for 10 minutes in room
temperature, white erystals appeared.

‘Then this solution was poured into ice-cold water.

‘The white crystals were fitered through Buchner funnel and the solid was dried.

Green Contest: carried out in aqueous medium, chlorinated solvents are avoided, use of acetic acid as
solvent is avoided and reaction is considerably fast.

Note: This reaction can be used for making bromo-derivative of acetanilide in Identification of organic
compounds.

Report: Yield ofthe crude sample = Mg
Melting point of the crystallized sample = 165°C
Calculation of theoretical yield:

ram molecular weight of p-Bromo acetanilide.
148 of p- Bromo acetanilide.

2X go Acct give Ey of p- Bromo acti

‘Theoretical Yield (N) Experimental Yield (M)

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CHEMISTRY nee 28132

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1B.Sc. 1 Semester Chemistry Lab Manual @

Experiment No. 5: Hydrolysis of methyl m-nitrobenzoate to m-nitrobenzoic acid (Conventional
method).

Aim: To prepare m-nitrobenzoic acid from methyl m-nitrobenzoate (Conventional method).
‘Theory: m-Nitrobenzoic acid can be prepared by the nltration of benzoic acd by means ofnivicacid a mixture
‘ofnitricand sulfuric acids or mintures of nitrates and sulfuric aci: these methods lead tothe production ofa
‘mixture containing principally the m-nitrobenzoic acid with a smaller proportion of the ortho and 1-2 per cent of
‘the para isomer, Nitration of benzo trichloride with subsequent hydrolysis also furnishes m-nitrobenzoic aca

or ae ey

Procedure:

+ In around-bottomed Mask ited with arefux condenser are placed a solution of2 y. (0.05 moles)
‘of sodium hydroxide in 20 ce of water (Note 1) and 45 g. of methyl m-nitrobenzoate

+ The mixture is heated to bolling during ive to ten minutes or until the saponification is complete as
shown by the disappearance ofthe ester:

‘+The reaction mixture I now diluted with a equal volume of water, and when coo! is poured, with string
Into 10 cc.of concentrated hydrochloric acid (Note 2)

‘+ After the solution has cooled to room temperature, the m-nitrobenzoic acid is filtered off by means of
suction

+ This crude acid when dry weighs is 90-96 por cent ofthe theoretical amount.

‘+ Ithas alight brownish colour, melts at 140%, and shouldbe completely soluble In ether, thus showing the
absence of salts

‘+ This acid Is satisfactory for many purposes, but inorder to prepare a perfectly pure product it must be
crystallized once from 1 per cent aqueous hydrochloric acid (Note 3). À light cream-colored product is
thus obtained with ose of bout Sper cent ofthe material (Note 4)

Notes:

1. The use of a more dilute sodium hydroxide solution than that recommended above has been found to
yield unsatisfactory results in the saponification of the este. Prolonged boiling may lead to the
production of coloured products

2. After the hydrolysis of the methy mnitrobenzoate tis essential thatthe solution ofthe sodium salt be
poured into the acid. acid is added tothe salt in the usual way, a less soluble aid salt separates; and, as
this cannot be entirely removed from the m-nitrobenzoic acid even on long digestion with hydrochloric
‘cia products obtained which does not dissolve completely in eter.

3. m-Nitrobenzoie acd is soluble tothe extent of 1 part in 300 parts of water at 20%, and 20 parts a 100°
‘The crystallization from water or dute hydrochloric acid 1 therefore quite saisactoy.

4. mNitrobenzoic acidis obtained in a higher yield by nitration of methyl benzoate with subsequent
hydrolysis than by the direct nitration o benzoic acid; this method is also preferable on account ofthe
Iaborfous nature of the methods necessary forth separation of the meta acd from the small quantities of
the para isomer formed inthe later process

Report Yield ofthe crudo sample = M = 8
Meling point of the crystallized sample = 140°C
DEPARTMENT OF CHEMISTRY Powe 29132

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1 BSc. 1 Semester Chemistry Lab Manual
Cateutation of theoretical led:
1 gram molecular weight of Methyl m-Nitro benzoate #1 gram molecular weight of m-Nitro benz acid

181. 15g of Methyl m-Nitro benzoate = 167.12g of m-Nitro benzoic acid.

Xy. of met ntroenzoate gives BIE «Ng of mntrobenzolcci
7 IS
‘hese Viel) | Esperimental Vic

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32. 1 B.Sc. 1 Semester Chemistry Lab Manual

‘Experiment No. 6: Synthesis of diazoaminobenzene from aniline (Conventional method).
Aim: To prepare diazoaminobenzene from aniline (Conventional method).
Theory:

Diazoaminobenzene has been prepared by the action af sodium nitrite on aniline sulphate;by the action
ofsodium nitriteon aniline hydrochlride:by the action ofsodium nitrite and sodium acetate on aniline
hydrochloride: by the action of ammonium nitrate and hydrogen sulfide on aniline hydrochloride inthe presence
ofiron;by the action ofsodium mititeandpotasstum chromate or dichromate on aniline and
{rom aniline and amyl nitrite,

Diazoaminobenzene has also been prepared by the action of nitrous acid gas on aniline in alcohol: by the
action of silver nitrite on aniline hydrochloride; and together with phenyl urea by the action ofnitroso phenyl
‘urea on aniline in methyl alcohol. Niementowski and Roszkowskihave reported studies on the diazotizaion
ofanitin aniline hydrochloride, and aniline sulphate with sodium nitriteand silver alte. The procedure
described is adapted from that of Fischer

Procedure:
+ In afaskftted with a mechanical sürrer and adropping funnel are placed 1 kg. of cracked ice, 1.5 L of
water, 24 8 of a technical grade of nine, and Sal concentrated hydrechlori ac (sp. gr 118).
+ Thestirer is started, and a solution of tml of 95 per cent sodium nitrite in 10cc of water s added over a
Period of een minutes.
+ The reaction mixture is then stirred for teen minutes, and à solution of 36 g of rystaline sodium
acetate dissolved in 8 eof water Is added over a period of five minutes,
‘+ _Ayellow precipitate of diszoaminobenzene begins to form at once.
‘+ Strringis continued for fory-Ave minutes, keeping the temperature below 20° (Note 1)
‘+ The yellow dazoaminobenzene is ftered on a 19-em. Büchner funnel (Note 2), washed with cold water,
and then sucked as dry as possible and spread out ona shee of paper to dry (Note 3).
+ The product thus obtained Is recrystallized by dissolved in of boilingligroin (hp. 60-90" (Note 4),
filtered, and allowed to cool to room temperature and stand overnight
Notes:
1. The temperature noted is not known tobe the maximum temperature at which the reaction maybe ru,
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33. 1 Semester Chemistry Lab Manual

2. Acentrilugeofsulabl sizes preferable.

3. Arubber dam is ted aver the top of the Buchner funnel and held in place by rubber bands in order to
remove as much ofthe water as possible.

4. Prolonged heating ofthe diazoaminobenzene with igron causes decomposition. For this reason its well
te heat the gro o boiling before its added tothe product to be crystallized. Slution s affected as
rapidly as posible. I the crudediazoaminobenzene is not dry, a layer of water will separate at the
bottom of the flask This should be removed as completely as possible before filtering the
hot iron solution.

Report: Yield ofthe crude sample = M =. $

Melting point ofthe crystallized sample = 140°C

Calculaion of theoretical yield:
1 gram molecular weight of Aniline =! gram molecular weight of diazoaminobenzene

932 of Methyl m-Nitro benzoate = 197.24 ofm-Nitro benzo acid,

+g omy matrbenzate gives 22222 = Ne of noble ac

| %of Yield
‘Theoretical Yield 0) Experimental Yield (M) |

L

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