Experiment- 1
Aim:
Determine the surface tension of a given liquid at room temp using
stalgmometer by drop number method
Requirements:
Stalgmometer, specific gravity bottle, a small rubber tube with a screw pinch
cork, distilled water, experimental liquid.
Theory:
In the drop number method, the number of drops formed by equal volumes
of two liquid is counted. If m1 and m2 is the mass of one drop of each of the
liquid having densities d1 and d2 respectively. If n1 and n2 is the number of
drops formed by volume v of the two liquids, then their surface tensions are
related as
¥1/¥2= (d1/d2)*(n2/n1)
One of the liquid is water its surface tension and density are known.Then te
surface tension of the given liquid can be calculated.
Procedure:
1. Clean the stalgmometer with chromic acid mix, wash with water and dry
it
2. Attach a small piece of rubber tube having a screw pinch cock at the
upper end of the stalgmometer.
3. Immerse the lower end of the stalgmometer in distilled water and suck the
water 1-2cm above mark A. adjust the pinch cork so that 10-15 drops fall per
minute
4.Clamp the stalgmometer allow the water drops to fall and start counting
the number of drops when the meniscus crosses the upper mark A and stop
counting when the meniscus passes mark B
5. Repeat the exercise to take three to four readings
6. Rinse the stalgmometer with alcohol and dry it
7. Suck the given liquid in the stalgmometer and count the drops as in case
of water
8. Take a clean dry weighing bottle weighs it with water as well as with
liquid.
9. Note the temp of water taken in a beaker.
Observations:
Room temp=t0C
Density of water=dw
Surface tension of water=¥ dynes/cm
No of drops From a Fixed Volume
Mean
Liquid
1….
2……
3…..
nl=
Water
1….
2…….
3……
nw=
Weight of empty specific gravity bottle=w1gram
Weight of specific gravity bottle+water=w2 gram
Weight of empty sp.gravity bottle+liquid=w3gram
Weight of water= (w2-w1)gram
Weight of liquid= (w3-w1)gram
Calculations:
Density of the liquid
Dl= (w3-w1)/(w2 –w1) *dw
Surface tension of liquid=
¥l/¥w = (dl/dw)*(nw/nl)* ¥w
Result
The surface tension of liquid is ………dynes/cm.
Experiment-2
Aim- Determine the surface tension of a given liquid by means of
stalgmometer using drop weight method.
Requirements- Stalgmometer , wide mouthed weighing bottle , a small
rubber tube with screw pinch cork, distilled water, experimental liquid.
TheoryThe size of the drop of liquid forming on a capillary end depends upon the
surface tension of the liquid. The drop falls when the total surface 2πr¥ is
equal to its weight (w)
i.e. w= mg= 2πr¥
if two liquids having surface tension ¥1 and ¥2 are allowed to fall through
the same capillary then
w1/w2 = m1/m2 = ¥1/¥2
Procedure1. Clean the stalagmometer with chromic acid mixture , wash with water
then with alcohol and dry it.
2. Attach a small piece of rubber tube having a screw pinch cork at the
upper end of the stalgmometer.
3. Immerse the lower end of the stalgmometer in distilled water and suck
the water 1-2cm above the mark A. Adjust the pinch cork so that 1015 drops fall per minute.
4. Clamp the stalgmometer and allow 10 drops of water to fall into the
pre-weighed wide mouthed weighing bottle.
5. Weigh the weighing bottle along with 10 drops of water. Repeat the
experiment three to four times.
6. Rinse the stalgmometer with the given liquid, dry it. Fill it with the
experimental liquid and the repeat the above steps.
ObservationsRoom temperature = toC\
Density of water = dw
Surface tension of water= ¥w
Weight of empty weighing bottle=w1g
Weight of weighing bottle+ 10 drops of water=w2 gram
Weight of bottle+ 10 drops of liquid=w3gram
Weight of water= (w2-w1)gram
Weight of liquid= (w3-w1)gram
Calculations¥l/¥w= (w3-w1)/(w2- w1)
ResultThe surface tension of the given liquid is …………………. Dynes/cm
EXPERIMENT 3
Aim: To determine the viscosity of a given unknown liquid with respect
to water, at laboratory temperature, by viscometer.
Requirements: Ostwald viscometer, rubber tube with screw pinch cock,
stand, beaker, unknown liquid, distilled water. specific gravity bottle
Theory: The force of friction which one part of the liquid offers to another
part of the liquid is called viscosity. For measuring the viscosity coefficient,
Ostwald viscometer method is used which is based on Poiseuille’s law.
According to this law, the rate of flow of liquid through a capillary tube
having viscosity coefficient, , can be expressed as

  r 4tP
8vl
where, v= vol. of liquid (in ml)
t= flow time (in sec.) through
capillary
r=
radius
of
the
capillary (in cm)
l= length of the capillary (in cm)
P= hydrostatic pressure (in dyne/sq.cm)
= viscosity coefficient (in poise).
Since, the hydrostatic pressure (the driving force) of the liquid is given by P
= dg h (where h is the height of the column and d is the density of the
liquid);
 P t ;
or,
d g h t
If, 1 and 2 are the viscosity coefficients of the liquids under study, d1, d2
, are their densities and t1 and t2 are their times of flow of equal volume of
liquids through the same capillary respectively, then
1  d1 g h t1 and 2 
d2 g h t2
1
Hence,
2

d1t1
d 2t2
Here, usually the viscosity of given liquid is measured with respect to water
whose viscosity is known very accurately at different temperatures. The SI
physical unit of viscosity is the pascal-second (Pa·s), (i.e., kg·m−1·s−1). This
means: if a fluid with a
viscosity of one Pa·s is placed between two plates, and one plate is pushed
sideways with a shear stress of one pascal, it moves a distance equal to the
thickness of the layer between the plates in one second. The cgs unit for the
same is the poise (P), (named after J. L. Marie Poiseuille). It is more
commonly expressed, as centipoise (cP). [1 cP = 0.001 Pa·s]. Water at 20
°C has a viscosity of 1.0020 cP.
Procedure:
1. Note the laboratory temperature.
2. Wash the specific gravity bottle with distilled water and dry.
3. Take the weight of the empty & filled (with distilled water) specific
gravity bottle (with stopper). Then, weigh the filled with specific gravity
bottle h unknown given liquid. Use the data for measuring the densities.
4. Clean and rinse the viscometer properly with distilled water. Fix the
viscometer vertically on the stand and filled with specific amount (say 20ml)
of mixture (every time take the same volume).
5. Time of flows were recorded for each solutions (water and the given
liquid).
6. Take 3 to 4 readings.
Observations:
1. Laboratory temperature=…. C
2. Density measurement:
Weight of empty R.D.bottle (w1) =…g.
Weight of R.D.bottle with water (w2) =…g.
Weight of R.D. bottle with liquid (w3) =…g.
So, weight of water (ww) = (w2-w1) =…g.
Flow
(sec)
Sl no.
t1
t2
times
t3
mean
1
2
3
4
Calculations:
1. Determination of the density of the liquid (dl):
Density of liquid = Weight of liquid
(dl)
(wl) Weight of
Density of water water (ww)
(dw)
(Take density of water =1.0g/ml at
Density of liquid (dl )  wl
d w 25
ww
2. Determination of the viscosity of the liquid (l )
Viscosity
liquid, 
of
the

l
tl dl
t
d

w
w w
Result: The viscosity of the given liquid with respect to water at laboratory
temperature was found to be ……..cP.
______
Experiment-4
Aim- To verify Beer Lambert’s law for dichromate solution.
Theory-The primary objective of this experiment is to determine the
concentration of an unknown K2 Cr2 O7 solution. The K2 Cr2 O7 solution
used in this experiment has a blue color, so Colorimeter users will be
instructed to use the red LED. A higher concentration of the colored
solution absorbs more light (and transmits less) than a solution of lower
concentration.
You will prepare five of known concentration (standard solutions).
Each solution is transferred to a small, rectangular cuvette that is placed into
the Colorimeter or Spectrometer. The amount of light hat pene ra es the s
lution and strikes the photocell is used to compute the absorbance of each solu
on. When you graph absorbance vs. concentration for the standard solutions, a
direct relationship should result. The direct relationship between absorbance
and concentration for a solution is known s Beer’s law.
You will determine the concentr tion of n unknown K2 Cr2 O7 solution by
measuring its absorbance. By locating the absorba nce of the unknown on
the vertical axis of the graph, the
corresponding concentration can be found on the horizontal axis. The
concentration of the unknown can a so be found using the slope of the
Beer’s law curve.
REQUIREMENTS
Colorimeter cuvette
five 20 × 150 mm test tubes
two 10 mL pipets or graduated cylinders two 100 mL beakers
0. 01M K2 Cr2 O7 solution
distilled water test tube rack stirring rod
tissues (preferably lint-free)
PROCEDURE
1. Obtain small volumes of 0. 01M K2 Cr2 O7 solution and distilled water in
separate beakers.
2. Label five clean, dry, test tubes 1–5. Use pipets to prepare five standard
solutions according to the chart below. Thoroughly mix each solution with a
stirring rod. Clean and dry the stirring rod between uses.
Test
Tube
1
2
3
4
5
0.01M
K2 Cr2 O7 . Distilled H2O Concentration
(mL)
(mL)
(M)
2
4
6
8
~10
8
6
4
2
0
0.002
0.004
0.006
0.008
0.0100
4. Prepare a blank by filling a cuvette 3/4 full with distilled water. To correctly
use cuvettes, remember:
 Wipe the outside of each cuvette with a lint-free tissue.
 Handle cuvettes only by the top edge of the ribbed sides.
 Dislodge any bubbles by gently tapping the cuvette on a hard surface.
Always position the cuvette so the light passes through the clear sides.
You are now ready to collect absorbance-concentration data for the five standard
solutions.
a. Using the solution in Test Tube 1, rinse the cuvette twice with ~1 mL
amounts and then fill it 3/4 full. Wipe the outside with a tissue and place it
in the device (Colorimeter or Spectrometer). Close the lid on the
b. Colorimeter.
c.
When
Discard
rinse
and
thethe
fill
absorbance
cuvette
the cuvette
readings
3/4
full.
stabilize,
directed.
Wipe the
Using
outside
the the
solution
andabsorbance
placeinthe
Test
cuvette
Tube in
2,
the
device
(close
thecontents
lid
of
theas
Colorimeter).
When
readings
stabilize,
d. Repeat the procedure for Test Tubes 3 and 4. Trial 5 is the original
0.01M K2 Cr2 O7 solution. Note: Do not test the unknown solution
e. until
WhenStep
you9.have finished testing the standard solutions
f.
10. Determine the absorbance value of the unknown K2 Cr2 O7 solution.
a. Obtain about 5 mL of the unknown K2 Cr2 O7 in another clean, dry, test
Record
the number
of the
insolution
your
data
b. tube.
Rinse
the outside
cuvette
twice
theunknown
unknown
andtable.
fill
it about
3/4of
full.
Wipe
the
Colorimeter.)
the
of
the with
cuvette,
place
it into
the device.
(Close
the lid
c. Read the absorbance value displayed in the meter. When the displayed
absorbance value stabilizes, record its value as Trial 6 in your data table.
d. Select Interpolate from the Analyze menu. Find the absorbance value that is
closest to the absorbance reading you obtained in Step c above. Determine
the concentration of your unknown K2 Cr2 O7 solution and record the
concentration in your data table.
e. Dispose of any of the remaining solutions as directed.
DATA TABLE
Trial
Concentration (mol/L)
1
0.002
2
0.004
3
0.006
4
0.008
5
0.010
6
Unknown number
____
Absorbance