DEPARTMENT
OF
CHEMISTRY
CHEMISTRY
LABORATORY
MANUAL
R.V.R. & J.C.COLLEGE OF ENGINEERING
CHANDRMAOULIPURAM :: CHOWDAVARAM
GUNTUR – 522 019 :: ANDHRA PRADESH
EE/ME/CE 151 & CS/EC/IT 161 - CHEMISTRYLAB
(R-20 Regulations)
Practicals : 3 periods/ week
Semester Exam. : 3 hrs
Internal Assessment: 30 Marks
Semester End Examination: 70 Marks
Credits: 1.5
Course Objectives:
1. To know the methods of determining hardness and chloride ion content of water sample.
2. To learn the redox methods to determine Fe2+ ions present in solution.
3. To know principles and methods involved in using instruments like conductivity bridge
and potentiometer
4. To know the molecular properties like surface tension, viscosity.
5. To know synthetic methods for preparation of drugs and polymer
Course outcomes:
After successful completion of the course student shall be able to
1. Estimate the Fe(II) content of a given solution and chloride/hardness content of water.
2. Measure conductance of solutions, redox potentials of a cell.
3. Synthesize a small drug molecule and polymer.
4. Measure molecular properties such as surface tension, viscosity and determine physical
parameters like saponification value, partition co-efficient and Rf value.
List of Experiments:
1. Estimation of Mohr’s salt using KMnO4.
2. Estimation of Mohr’s salt using K2Cr2O7.
3. Determination of chloride ion content of water.
4. Determination of Hardness of water using EDTA method.
5. Determination of Fe(II) strength using K2Cr2O7 potentiometrically.
6. Determination on strength of NaOH using HCI conductometrically.
7. Preparation of p-bromo acetanilide.
8. Preparation of Phenol Formaldehyde resin.
9. Determination of surface tension.
10. Determination of Viscosity.
CO1
CO1
CO1
CO1
CO1&2
CO2
CO3
CO3
CO4
CO4
PERMANGANOMETRY
Experiment No: 1
ESTIMATION OF MOHR’S SALT USING POTASSIUM PERMANGANATE
Aim: To estimate the amount of Mohr’s salt present in one litre of the given solution.
Apparatus required: Pipette, Burette, Conical flask, Wash bottle, Glazed tile, Burette stand.
Chemicals required: 1) Standard Mohr salt solution.
2) Potassium Permanganate solution.
3) Mohr’s salt solution. (Unknown)
4) 10% Sulphuric Acid.
Chemical Reaction:
10FeSO4 + 2KMnO4+ 8H2SO4
K2SO4 + 2MnSO4 + 5Fe2 (SO4)3 + 8H2O
Procedure:
Part A: Standardization of Potassium Permanganate:
10 ml of the standard Mohr salt solution is pipetted out into a clean conical flask. To
it 10 ml of 10% dilute sulphuric acid is added. The flask is kept underneath the burette and
the permanganate is run slowly, swirling the liquid in the flask at the same time. The
solution is run till the addition of a drop more of the permanganate solution gives a
permanent pink color to the solution present in the conical flask. This is the end point. The
reading of the burette is noted.
The titrations are repeated with 10 ml of ferrous ammonium sulphate solution,
till a concordant value is obtained. Results are entered in a tabular form.
Part B: Estimation of Mohr’s Salt Solution:
The given solution is made up to the mark with distilled water. 10 ml of the made up
solution is pipetted out into a clean conical flask. To it 10 ml of 10% dilute sulphuric acid is
added. The flask is kept underneath the burette and the permanganate is run slowly,
swirling the liquid in the flask at the same time. The solution is run till the addition of a drop
more of the permanganate solution gives a permanent pink color to the solution present in
the conical flask. This is the end point. The reading of the burette is noted.
The titrations are repeated with 10 ml of ferrous ammonium sulphate solution,
till a concordant value is obtained. Results are entered in a tabular form.
Observations & Calculations:
Part A: Standardization of Potassium Permanganate:
Molarity of Mohr’s salt solution=M1=
Sl.
Volume of Mohr’s salt
No.
Solution V1 ml
1.
10
2.
10
3.
10
Burette readings
Initial(a)
Volume of Potassium
permanganate (b-a) V2 ml
Final(b)
Mohr’s salt Solution
Potassium Permanganate
V1M1/n1
=
V2M2/n2
Volume of Mohr’s salt solution
=
V1 ml
Molarity of Mohr’s salt solution
=
M1
Volume of KMnO4 solution
=
V2 ml
Molarity of KMnO4 solution
=
M2
n1= No. of moles of Mohr salt in the balanced equation
=
10
n2 =No. of moles of KMnO4 in the balanced equation
=
2
=
M2
M2 =
V1M1 x n2
n1 V2
Therefore molarity of Potassium permanganate solution
Part B: Estimation of Ferrous Ammonium Sulphate (Mohr’s salt):
Molarity of Potassium permanganate solution M4=M2=
Sl.
Volume of Mohr’s salt
No.
Solution V3 ml
1.
10
2.
10
3.
10
Burette readings
Initial(a)
Volume of Potassium
Final(b)
Mohr’s salt
permanganate (b-a) V4 ml
Potassium Permanganate
V3M3/n3
=
M3
=
V4M4/n4
V 4M 4 n 3
n4 V3
Volume of Mohr’s salt solution
=
V3 ml
Molarity of Mohr’s salt solution
=
M3
Volume of KMnO4 solution
=
V4 ml
Molarity of KMnO4 solution
=
M4
n3 =No. of moles of Mohr’s salt in the balanced equation=10
n4 =No. of moles of KMnO4 in the balanced equation=2
Therefore molarity of Mohr’s salt solution =
M3
Amount of Mohr’s salt present in one litre of the given solution
=
Molarity x Molecular wt. x Vol. in lts.
=
M3 x 392.15 X 1
=
................ gms
Result: Amount of Mohr’s salt present in one litre of the given solution =
gms
DICHROMETRY
Experiment No.:2
ESTIMATION OF MOHR’S SALT USING POTASSIUM DICHROMATE
Aim: To estimate the amount of Mohr’s salt present in 1 litre of the given solution.
Apparatus required: Pipette, Burette, Conical flask, Wash bottle, Glazed tile, Burette stand.
Chemicals required: The following solutions are required.
1) Standard Mohr’s salt solution.
2) Potassium Dichromate.
3) Mohr’s salt solution.
4) 25% Sulphuric acid.
5) N-Phenyl anthranilic acid.
Chemical equations:
K2Cr2O7 + 6FeSO4 + 7H2SO4
K2SO4 + 3Fe2 (SO4)3 + Cr2 (SO4)3 + 7H2O
Procedure:
Part A: Standardization of Potassium Dichromate:
10ml of standard Mohr’s salt solution is pipetted out into a conical flask. 10 ml of
25% sulphuric acid is added. Then 5 or 6 drops of N-Phenyl anthranilic acid is added. Now
the solution in the conical flask is colorless. The dichromate solution is run from the burette
till the solution becomes green. This is before the end point. The titration is continued until
the solution color suddenly turns red violet. This is the end point. The volume of the
potassium dichromate added is noted from the burette reading. The experiment is
repeated until a concurrent value is obtained.
Part B: Estimation of Mohr’s salt:
The given solution is made up to the mark using distilled water. 10 ml of made up
Mohr’s salt solution is pipetted out into a conical flask. 10ml of 25% sulphuric acid is added.
Then 5 or 6 drops of N-phenyl anthranilic acid is added. Now the solution in the conical flask
is colorless. The dichromate solution is run from the burette till the solution becomes green.
This is before the end point. The titration is continued until the solution color suddenly
turns red violet. This is the end point. The volume of the potassium dichromate added is
noted from the burette reading. The experiment is repeated until a concordant value is
obtained.
Observations & Calculations:
Part A: Standardization of Potassium Dichromate:
Molarity of Mohr salt solution= M1=
Sl.
Volume of Mohr’s Salt
No.
solution V1 ml
1.
10
2.
10
3.
10
Burette readings
Initial (a)
Volume of Potassium
Dichromate (b-a) V2 ml
Final (b)
Volume of Mohr’s salt solution
=
V1 ml
Molarity of Mohr’s salt solution
=
M1
Volume of Potassium Dichromate used
=
V2 ml
Molarity of Potassium Dichromate solution
=
M2
n1=No. of moles of Mohr’s salt in the balanced equation
=
6
n2 =No. of moles of K2Cr2O7 in the balanced equation
= 1
By using the formula: V1M1/n1
M2
=
=
V2M2/n2
V 1M 1 n 2
n 1 V2
Molarity of Potassium Dichromate solution =M2 =
Part-B: Estimation of Mohr’s salt:
Molarity of Potassium Dichromate solution =M2=
Sl.
Volume of Mohr’s Salt
No.
solution
V3 ml
1.
10
2.
10
3.
10
Burette readings
Initial (a)
Final (b)
Volume of Potassium
Dichromate V4 (b-a) ml
Volume of Mohr’s salt solution
=
V3 ml
Molarity of Mohr’s salt solution
=
M3
Volume of Potassium Dichromate used
=
V4 ml
Molarity of Potassium Dichromate solution
=
M4
Potassium Dichromate
Mohr’s salt solution
V4M4/n4
=
M3 =
V3M3/n3
V4M4n3
n 4 V3
Molarity of Mohr’s salt solution = M3
Amount of Mohr’s salt present in one litre of the given solution
=
Molarity x Molecular wt x Vol. in lts.
=
M3x 392.15 x1 =
Result:
Amount of Mohr’s salt present in one litre of the given solution=
gms
Experiment No.:3
ESTIMATION OF CHLORIDE IN WATER
Aim: To determine the chloride content of the given sample of water using silver nitrate
Solution with potassium chromate as an indicator. (Mohr’s indicator)
Apparatus required: Pipette, Burette, Conical flask, Burette Stand, Wash bottle, Glazed tile,
volumetric flask and beaker.
Chemicals required: a) Standard sodium chloride solution.
b) Silver nitrate solution.
c) Potassium chromate solution.
d) Water sample.
Chemical Reactions:
AgNO3 + Cl2AgNO3 + K2CrO4
Yellow
AgCl + NO3Ag2CrO4 + 2KNO3
Red
Procedure:
Part A: Standardization of Silver nitrate solution:
10 ml of the standard sodium chloride is pipetted into a conical flask keeping it upon
a tile. To it 1 ml of the indicator solution is added. The solution colour changes to yellow.
This solution is titrated slowly with silver nitrate solution from the burette, swirling the
solution constantly until the red color formed by the addition of each drop begins to
disappear more slowly. This is an indication that more of the chloride has been precipitated,
change in the color occurs. At the end point a faint reddish tinge persists after brisk shaking.
The final burette reading is noted. The titration is repeated until a concordant value is
obtained. The molarity of silver nitrate solution is calculated.
Part B: Estimation of Chloride content in water:
After standardizing the silver nitrate solution the titration is repeated with water
sample. 20 ml of the water sample is pipetted into a conical flask keeping it upon a tile. To it
1 ml of the indicator solution is added. The solution colour changes to yellow. This solution
is titrated slowly with silver nitrate solution from the burette, swirling the solution
constantly until the red color formed by the addition of each drop begins to disappear more
slowly. This is an indication that more of the chloride has been precipitated, change in the
color occurs. At the end point a faint reddish tinge persists after brisk shaking. The final
burette reading is noted. The titration is repeated until a concordant value is obtained.
Observations & Calculations:
Part A: Standardization of silver nitrate:
Molarity of NaCl =M1=
Sl.
No.
Volume of Sodium
Chloride V1 ml
1.
10
2.
10
3.
10
Burette readings
Initial (a)
Volume of Silver nitrate
=
V2 ml
Molarity of Silver nitrate
=
M2
Volume of Sodium chloride =
V1 ml
Molarity of Sodium chloride =
M1
Final (b)
n2 =No. of moles of AgNO3 in the balanced equation = 1
n1= No. of moles of NaCl in the balanced equation = 1
Volume of Silver Nitrate
Solution (b-a) V2 ml
V1M1/n1
=
V2M2/n2
M2 = V1M1 x n2
n1V2
Therefore molarity of silver nitrate solution ( M2 ) =
Part B: Estimation of Chloride in water:
Molarity of silver nitrate solution = M2=
Sl.
Volume of water sample
No.
Burette readings
Initial (a)
1.
20 ml
2.
20 ml
3.
20 ml
Final (b)
Volume of Silver Nitrate
used (b-a)
1000 ml of 1M AgNO3 = 35.46 grams of chloride
V3 ml of M2 AgNO3 is equivalent to V3M2 x 35.46 grams of chloride
1000
20 ml of water sample contains V3M2 x 35.46 grams = X grams of chloride
1000
1000 ml of water sample contains
50 x X grams of chloride
5x104 x X mg of ClChloride content of given water sample =
ppm
Result: Chloride content of given water sample………. ppm
V3 ml
Experiment No.:4
DETERMINATION OF TOTAL HARDNESS OF WATER
Aim: To determine the total hardness of water using EDTA.
Chemicals required: 1) Standard Zinc salt solution.
2) EDTA solution.
3) Eriochrome Black T indicator.
4) Ammonia and Ammonium chloride buffer solution.
5) Water sample.
Chemical equations:
Na2H2Y
H2Y2- + 2Na+
H2In-
↔ HIn2- ↔ In3-
Red
Blue
Yellow/Orange
Part A: Standardisation of EDTA:
In2- + Mg2+
MgIn- + H+
Wine red
Mg2+ + H2Y2-
MgY2- + 2H+
MgIn- + H2Y2- MgY2- + HIn2- + H+
(Wine red)
(Blue)
Part B: Determination of total hardness of water: (M= Ca and Mg)
M2+ + HIn2M2+ + H2Y2MIn- + H2Y2-
MIn- + H+
MY2- + 2H+
MY2- + HIn2- + H+
(Wine red)
(Blue)
Procedure:
Part A: Standardisation of EDTA:
The burette is filled with EDTA and the lower meniscus is adjusted to the zero mark.
10 ml of standard magnesium salt solution is pipetted into a 250 ml conical flask. 2 ml of
ammonia and ammonium chloride buffer solution and 2 to 3 drops of Eriochrome Black T
indicator is added. The solution becomes wine red in colour which is titrated with EDTA
from the burette till the colour changes to blue. The burette reading is noted. The titration is
repeated for a concordant value.
Part B: Determination of total hardness of water:
50 ml of water sample is pipetted into a clean conical flask. 2 ml of ammonia and
ammonium chloride buffer solution and 2 to 3 drops of Eriochrome Black T indicator is
added. The solution becomes wine red in colour which is titrated with EDTA from the
burette till the colour changes to blue. The burette reading is noted. The titration is
repeated for a concordant value.
Observations & Calculations:
Part A: Standardization of EDTA:
Molarity of Magnesium salt solution=M1=
Sl.
No.
Volume of magnesium
salt solution V3 ml
1.
10
2.
10
3.
10
Burette readings
Initial(a)
Volume of EDTA added
(b-a) V2 ml
Final(b)
Magnesium Sulphate
EDTA
V1M1/n1
Molarity of EDTA solution
=
M2
=
V2M2/n2
V1M1n2
n1V2
Part B: Determination of total hardness of water:
Molarity of EDTA =M2=
Sl.
Volume of water sample
No.
V3
1.
50 ml
2.
50 ml
3.
50 ml
Burette readings
Initial(a)
Final(b)
Volume of EDTA added
(b-a) ml
V4
1000 ml of 1M EDTA = 100 gm of CaCO3
V4 ml of M2 EDTA = V4 x M2 x 100/1000 gm CaCO3
50 ml of water contains V4 x M2 x 100/1000 gm CaCO3
1000 ml of water contains V4 x M2 x 100/50 gm CaCO3
= X gm CaCO3
= X x 1000 mg CaCO3
Result:
Total hardness of given water sample is__________ ppm of CaCO3
Experiment No. 5
POTENTIOMETRIC TITRATION
DETERMINATION OF IRON (II) USING POTASSIUM DICHROMATE
Aim: To determine the concentration of Iron (II) using Potassium dichromatePotentiometrically.
Apparatus required: Potentiometer, Calomel electrode, Platinum electrode, beaker, wash
bottle, magnetic stirrer, measuring jar.
Chemicals Required: Ferrous ammonium sulphate, sulphuric acid, potassium dichromate.
Theory: The reduction potential of Cr (III) / Cr (VI) solution system is 1.36 Volts and that of
Fe (III) / Fe (II) system is 0.76 volts. Since dichromate system has high reduction potential
value it can oxidize iron (II) to iron (III). In order to maintain acidity, sufficient sulphuric acid
must be added.
Indicator Electrode
Pt / Fe (II), Fe (III)
E0 = + 0.76 V
Calomel Electrode
Hg, Hg2Cl2 / KCl (Sat) E0 = 0.24 V
(ref. Electrode)
Cell Representation
Hg, Hg2Cl2 / KCl Sat || Fe (II), Fe (III) | Pt
Above cell emf can be measured by potentiometer.
In the above cell:
Ecell
= EFe(III)/Fe(II) – Ecalomel
Ecell

0.0591
Fe ( II ) 
= 0.76V −
log
− 0.24
1
Fe ( III ) 

= 0.52V −
0.0591
Fe ( II )
log
1
Fe ( III )
During the titration of Fe (II) solution with K2Cr2O7, the concentration of Fe (II) decreases
and Ecell value increases.
Preparation:
1.
2.
3.
0.05 N Potassium dichromate: About 0.613 gr. of potassium dichromate is
weighed accurately and transferred into a 250 ml volumetric flask. The
compound is dissolved in distilled water and made upto the mark. Normality of
the solution is calculated from the weight of K2Cr2O7.
0.05 N Iron (II) Solution: About 4.99 gr. of ferrous ammonium sulphate is
weighed and transferred into a 250 ml volumetric flask. Compound is dissolved
in distilled water and made upto the mark.
10 N H2SO4 Solution: It is prepared by mixing 28 ml con. H2SO4 and 72 ml water.
Procedure:
10 ml of iron (II) solution is transferred into a 150 ml beaker. 40 ml of 10 N H2SO4
solution and 50 ml distilled water are added to it. A platinum electrode is dipped into the
solution. A saturated calomel electrode is also immersed in the solution. The lead wires of
platinum electrode and calomel electrode are connected to respective terminals on
potentiometer. Ecell can be read from potentiometer.
Potassium dichromate solution (0.05N) is added in equal increments. Solution in the
beaker is uniformly agitated with the help of magnetic stirrer. After the addition of each
increment cell potential is measured and noted.
A graph is drawn between e.m.f of the cell and volume of potassium dichromate.
The equivalence point of titration is noted as the value where maximum change in e.m.f
with unit volume addition of potassium dichromate is observed.
Observations:
S.No.
Graph:
Volume of K2Cr2O7
in ml
E.M.F in
milli volt
Calculations:
Fe (II)
V 1N 1
K2Cr2O7
=
V2N2
10 x N1= Vgraph X 0.05
N1= Vgraph X 0.05/10
Result: Concentration of iron (II) solution is ______N
[Type here]
Experiment No. 6
CONDUCTOMETRIC TITRATION
Determination of strength of NaOH
Aim: To determine the molarity of given sodium hydroxide solution.
Apparatus required: Micro burette, pipette, glass rod, Conductometer
Chemicals required: Standard hydrochloric acid, sodium hydroxide.
Chemical Reaction: NaOH + HCl
NaCl + H2O
Procedure:
The instrument is switched on and left for 15 minutes to warm up. The conductivity
cell is connected to the conductometer and the cell constant is fixed at 1. 10 ml of 0.1M HCl
and 90 ml of distilled water are taken in a 250 ml beaker. The conductivity cell is completely
immersed into the beaker containing the solution. The range switch is kept in a position
where conductivity of the solution in the beaker is read from the digital display. NaOH in 1
ml increments is added to HCl and the corresponding conductance is noted. A graph is
drawn by plotting conductance versus volume of sodium hydroxide added. The point of
intersection of the two straight lines gives the end point of the titration.
Precautions: Stirring should be done after each addition of sodium hydroxide.
[Type here]
Observations:
S.No.
Volume of
NaOH (in ml)
Conductance
(in mS)
Graph:
Conductance
(mS)
Vol. of NaOH added (in ml)
[Type here]
Calculations:
HCl
V1M1/n1
NaOH
=
V2M2/n2
As n1= n2 =1;
V1M1 = V2M2
M2 = V1M1/V2 = 10 x 0.1 / Vgraph
Result: The concentration of NaOH solution is
[Type here]
M
Experiment No. 7
Preparation of p-Bromoacetanilide
Reagents:
Acetanilide
..
5 gms
Gl. acetic acid
..
50 ml
Bromine
..
2 ml
Procedure: Dissolve 5 gms, of acetanilide in 2.5 ml. of glacial acetic acid in a 250 ml. conical
flask. In another small flask, dissolve 2 ml. of bromine in 25 ml. of glacial acetic acid and
transfer the solution to a burette. Stand the flask in iced water bath and add bromine
solution drop wise slowly and regularly shaking the flask to ensure thorough mixing. After
the addition of all bromine, the solution will become of orange colour due to slight excess of
bromine. Allow the mixture to stand at room temperature for about half an hour with
occasional shaking. Pour the contents with stirring to about 250 ml. cold water in a beaker.
Filter and wash the product with cold water and dry. Recrystallise 1 gm. of the product from
ethyl alcohol.
Yield
: 6 gms
M.P
: 1670C
Colour
: Colourless crystals.
[Type here]
Experiment No.:8
PREPARATION OF PHENOL FORMALDEHYDE RESIN
Aim: To prepare phenol formaldehyde resin.
Apparatus required: Beaker, glass rod, glass funnel etc.,
Chemicals required: Glacial acetic acid, 40% Formaldehyde solution, phenol, concentrated
HCl.
Reactions:
OH
HCHO
CH2
CH2
OH
OH
Procedure: Place 5 ml of glacial acetic acid and 2.5 ml of 40% formaldehyde solution in a
500 ml beaker and add 2 grams of phenol, wrap a cloth of a towel loosely round the beaker.
Pass dry HCl gas (or less preferably a few ml of concentrated HCl) into the mixture carefully.
Within 5 minutes, a large mass of pink plastic is formed (if concentrated HCl is used slight
heating is required). The residue obtained is washed several times with distilled water and
filtered product dried and yield is calculated.
Precautions:
1. The reaction is some times vigorous and at in better to be few feet away from the
beaker while adding the HCl and until the reaction is complete.
2. The experiment should be preferably carried out in fume cupboard.
[Type here]
Experiment No. 9
SURFACE TENSION
Object : To determine the surface tension of the given liquid at room temperature by
stalagmometer.
Theory
The surface tension of the given liquid is determined relative to water at the roomtemperature by using stalagmometer. The no. of drops for the same volume of water and the given
liquid are counted and let these be as n1 and n2 respectively. Now if d1 and d2 are densities of water
and the given liquid at the room temperature as determined separately by using specific gravity
bottle or pyknometer, then the surface-tension 2 of the given liquid can be calculated by using the
simplified relationship as:
 1 n2 d1
= 
 2 n1 d 2
Materials
Stalagmometer, distilled water, unknown liquid, beaker, rubber tube with screwpinch cock,
clamp stand, specific gravity bottle or pyknometer.
Description of the apparatus
The stalagmometer consists of a bulbed dropping tube with a capillary. The lower end of
capillary is well ground, polished and flattened in order to provide larger dropping surface. There
are two marks C and D above and below the bulb B. The upper end of the apparatus is connected
with a rubber tube with a screw pitch cock in order to control the rate of flow so that spherical drop
may be formed.
Hence by simply counting the number of drops for the given liquid and water and knowing
their density, we can find the relative surface tension of the liquid. The advantages of the droppipette method are that it is very convenient and quick. It can also be employed for determinations
at different temperatures by placing the whole apparatus in a thermostat.
[Type here]
Procedure
1. Clean the stalagmometer, a specific gravity bottle or pyknometer thoroughly first with
chromic acid solution and wash finally with distilled water and then dry.
2. By immersing lower end in a beaker containing distilled water, suck up water until it rises
above the mark C and tighten the screw of the screwpinch.
3. Now loosen the screw of the screw-pinch carefully so that the liquid drops start falling at an
interval of about 2-3 seconds in successive drops. Counting of drops is started when the
water meniscus just reaches the upper mark C, and stopped when the meniscus just passes
the lower mark D. Repeat to get three readings and take the mean value.
4. Clean the stalagmometer and dry it. Fill it with liquid until it rises above the upper mark C
and count the number of drops as before.
5. Clean and dry the specific gravity bottle and measure the density of liquid. The density of
liquid can also be determined by pyknometer.
Observations and Calculations
Room Temp. = ……….0C
Density of water at room temp. = d1
Weight of empty specific gravity bottle or pyknometer = w1g
Weight of specific gravity bottle or pyknometer with water = w2g
Weight of specific gravity bottle or pyknometer with liquid for the same volume as that of water =
w3g

Weight of water = (w2 – w1) = m1g (say)
and
Weight of liquid = (w3 – w1) = m2g
Surface tension of water at room temp. = say (16.8)
[Type here]
Liquid
No. of drops
(1)
(2)
Mean value
(3)
Water
n1
Given Liquid
n2
Calculations
Density of the given liquid relative to water at room temperature.
m2
= d2
m1
Also
 1 n2 d1
= 
 2 n1 d 2

2 = 1 x
n1 d 2

n2 d1
Where 1 = surface tension of water at room temp.
Substituting the values of 1, n1, n2, d1 and d2, the surface-tension of the given liquid at room
temperature thus becomes known.
Result
The relative surface tension of liquid with respect to water at room temperature is……
………….
[Type here]
Precautions
1.
2.
3.
4.
5.
The stalagmometer and specific gravity bottle or pyknometer should be cleaned
properly and dried before use.
Fit the stalagmometer vertically.
The rate of the fall of drops should be adjusted in a way of having interval of at least 2-3
second in successive drops. The number of drops per minute must be in between 15-20.
The drops should fall from the tip of the stalagmometer under their own weight rather
than pushing them by force.
Wash and dry the stalagmometer after use.
Stalagmometer
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Experiment No. 10
VISCOSITY
Object
Determine relative viscosity of liquid with respect to water at room temp. by Ostwald’s
viscometer.
Apparatus
Distilled water, stop watch, viscometer (Ostwald’s), unknown liquid, pyknometer or R.D.
bottle, pipette etc.
Description
Ostwald’s viscometer is a U-shaped glass tube as shown in the Fig. In one arm, the bulb A is
connected with a fine capillary. The lower end of the capillary is connected with a U-tube provided
with a bulb B in the second arm. The bulbs are necessary to maintain the hydrostatic pressure
during flow of liquid. Through the capillary tube, the liquid flows with measurable speed. There are
two marks C and D above and below the bulb A. The upper end of the bulb A is attached with a
rubber tube. The liquid flows under its own weight.
The density of liquid is determined either by pyknometer or by R.D. bottle.
Theory
The measurement of viscosity by viscometer is based on the Poiseulle’s equation, which is
=
[Type here]
 Pr 4 .t
8V .l
… (1)
V = volume of liquid of viscosity  flowing in the time t, through the capillary
where
tube of radius r and length l.
P = Pressure (hydrostatic pressure) of liquid.
If t1 and t2 are times required to flow for equal volumes of two liquids through the same
length of a capillary tube, then from equ. (1) We have
1 P1.t1
=
2 P2t2
… (2)
The pressure of liquid = h.d.g
Since for two liquids h and g are same, hence
P1 d1
=
P2 d 2
Therefore
… (3)
1 d1.t1
=
2 d 2 .t2
Where d1 and d2 are the densities of two liquids.
If
1 = Viscosity of the liquid.
2 = Viscosity of water
Then
[Type here]
1
= Relative viscosity of liquid with respect to water.
2
… (4)
Relative viscosity has no unit.
Procedure
Clean the viscometer with chromic acid and then wash thoroughly with distilled water. It is
finally washed with alcohol or acetone and then dried. A sufficient volume of distilled water is
introduced by pipette in bulb B so that the bend portion of tube and half or a little more than half of
bulb B are filled up. Clamp the viscometer in quite vertical position. Through the rubber tube
attached to upper arm of a bulb A, suck up water until it rises above the upper mark C and allow it to
flow under its own weight. The time of flow of water from C to D is counted by starting the stop
watch as the meniscus just reaches upper mark C and stopping the watch as the meniscus just
passes the lower mark D. Take at least 3 or 4 readings with water and then take the mean of them.
Now remove the water from viscometer and dry it. Introduce in bulb B the same volume of
liquid and measure the time of flow of liquid as before. Take at least 3 or 4 readings and then take
the mean value.
Now, wash and dry the pyknometer (or R.D. bottle) and then weight it empty. Then fill it
with distilled water and weigh. Remove water and dry. Then fill it with experimental liquid and
weigh. Note the room temperature.
Fig. Ostwald’s viscometer
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Observations
(1) Room Temperature…….
(2) Time of flow between C and D:
S.No.
Water
Time of flow
Liquid under experiment
Mean (t2)
Time of flow
1
…..
…..
2
…..
…..
3
…..
…..
4
…..
…..
Mean (t2)
(3) Density of liquid (d1) and of water (d2)
Mass of empty of R.D. bottle (or pyknometer)
=
….gm.
Mass of R.D. bottle (or pyknometer) + water
=
….gm.
Wt. of water
=
….gm.
Mass of R.D. bottle (or pyknometer) + liquid
=
….gm.
Mass of liquid
=
….gm.
Calculations
Density of liquid(d 1 ) wt. of liquid
=
Density of water(d2 ) wt. of water
Relative viscosity of liquid =
[Type here]
1 d1t1
=
 2 d 2t 2
By inserting the respective values, the relative viscosity of liquid is calculated.
Result
The relative viscosity of this liquid with respect to water, at room temp. is ……
Precautions
1. The viscometer should be thoroughly be cleaned before use.
2. Viscometer must be strictly kept in vertical position.
3. Observe accurately when the meniscus of liquid and water are just passing the upper
and lower marks.
4. Same volumes of water and liquid should be taken in viscometer.
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