This presentation is based on demonstration on the Determination of the molecular weight of high polyvinyl alcohol (pva) by viscosity method. The presentation is made for Undergraduate Chemistry Students of Mumbai University

1. Determination of the molecular weight of
high polyvinyl alcohol (PVA) by viscosity
method.
Dr. P. U. Singare
Associate Professor
Department of Chemistry
N.M. Institute of Science, Bhavan’s College,
Andheri, Mumbai 400 058

2. Understanding the basic concept
• Viscosity: is the resistance to flow of one layer of liquid over other layer. In case of liquid,
viscosity represent the concept of “thickness”, for example oil is has higher viscosity
(more thick) as compared to water which is having relatively low viscosity (less thickness).
• Unit of Viscosity: The SI unit of viscosity is the newton-second per square meter
(N·s/m2), also frequently expressed in the equivalent forms pascal-second (Pa·s)
and kilogram per meter per second (kg·m−1·s−1). The CGS unit is the poise (P) or
centipoise (cP).
• Conversion: 0.001 Pa.s = 1mPa.s = 1cP
A centipoise is one hundredth of a poise.
• Symbol of Viscosity: ƞ (eta)
• Liquid water has a viscosity of 0.00890 P at 25 °C at a pressure of
1 atmosphere (0.00890 P = 0.890 cP = 0.890 mPa⋅s).
• The viscosity of water at 20 °C is almost exactly 1 centipoise.

3. Different types of Viscometers
• Redwood viscometer
• Ubbelohde type viscometer
• Ostwald viscometer, also known as U-tube viscometer or
capillary viscometer

4. Ostwald viscometer
It consist of an U-shaped glass tube.
It is having 2 arms: arm 1 & arm 2.
It is having 2 bulbs: Bulb A (large capacity) &
Bulb B (small capacity).
Below the Bulb B there is a fine capillary glass
tube.
Below and above the bulb B there are 2
markings. Upper mark C and lower mark D.
The solution whose viscosity is to be determined
in introduced through Arm 1 in bulb A.
The solution is sucked by using the rubber bulb
or by mouth through arm 2 in upward direction
in the bulb B.
The viscometer is clamped to a burette stand
and the solution is allowed to flow down freely
in arm 2.
The time required by the solution to flow from
mark C to mark D is recorded in seconds using a
stopwatch.

5. Requirements
1. Ostwald Viscometer
2. 1% Polyvinyl alcohol (PVA) solution
3. Distilled water
4. Glass beakers (50 mL capacity)
5. Bulb Pipette (10 mL capacity)
6. Graduated pipette (10 mL capacity)
7. Stop watch

6. Procedure
• Cleaning of Viscometer
Add distilled water in Bulb A through the Arm 1.
Suck the water upward in Bulb B (Arm 2) by mouth suck
or by rubber bulb.
Push the water forcefully in downward direction by
blowing the Arm 2.
As a result, the water will move down forcefully through
the fine capillary tube.
When the water move down forcefully in the Arm 2
through the fine capillary tube, the capillary tube will
get clean.
Discard the cleaning water through the Arm 1.
Repeat the above steps many times using fresh water to
ensure the proper cleaning of capillary tube.
Note: In order to get proper readings, it is essential to
clean the capillary tube before and after taking the
readings.

7. Procedure (Continued----)
1. Wash/clean the capillary of Ostwald viscometer
using distilled water (as mentioned previously).
2. Clamp the clean viscometer to the burette stand.
3. By means of pipette, add 10 mL of distilled water in
bulb A.
4. Mouth suck the water through Arm 2 in bulb B, so that
water level will be above mark C.
5. Allow the water to flow down freely.
6. As the level of water touch the marking C start the
stop watch.
7. As the level of water touch the marking D stop the
stopwatch.
8. Record the efflux time (in seconds) required for water
to flow from mark C to mark D.
9. Using the same water take more number of readings by
repeating the above steps 4 to 8 till you get constant
readings (in seconds)

8. Procedure (Continued----)
10. Using 1% PVA stock solution, prepare
polymer solutions of 5 different
concentrations as shown in the Table.
11. Pipette 10 mL of 0.2% polymer solution and
introduce it in the bulb A of a viscometer.
12. Repeat the above procedure (steps 4 to 9) to
get constant readings of efflux time in
seconds for 0.2% polymer solution.
13. Clean the viscometer properly with distilled
water.
14. Measure the efflux time in seconds for higher
concentrations of PVA solutions (0.4%, 0.6%, 0.8% &
1.0%) by repeating the above procedure (steps 4 to
9).
Note: The viscometer should be cleaned every time
when you take the new polymer solution.
Flask
No.
Volume of
1% PVA
solution
Volume
of water
Total
volume
Final
Concentration (%)
1 4 16 20 0.2
2 8 12 20 0.4
3 12 8 20 0.6
4 16 4 20 0.8
5 20 0 20 1.0

9. Observations & Calculations
% Concentration of
Polymer solution
(C)
Efflux time
(s)
Ƞrel Ƞsp = ƞrel -1 Ƞsp/C
0%
(blank solution
having only water)
ts ---
0.10 t1 t1/ts = X1 X1-1 X1-1/0.10
0.25 t2 t2/ts =X2 X2-1 X2-1 /0.25
0.50 t3 t3/ts =X3 X3-1 X3-1/0.50
0.75 t4 t4/ts = X4 X4-1 X4-1 /0.75
1.00 t5 t5/ts =X5 X5-1 X5-1

10. Observations & Calculations (continued)
% Concentration of
Polymer solution (C)
Efflux time
(s)
Ƞrel Ƞsp = ƞrel -1 Ƞsp/C
1 2 3 Constant
reading
0%
(blank solution
having only
water)
93 95 93 93 - - -
0.10 106 106 109 106 1.14 0.14 0.700
0.25 131 136 131 131 1.41 0.41 1.025
0.50 145 147 147 147 1.58 0.58 0.960
0.75 176 176 182 176 1.89 0.89 1.110
1.00 198 198 198 198 2.13 1.13 1.130

11. Graph & Calculations
α = 0.76 K = 2x10-4 (GIVEN)
Mv =
α
ƞInt/K
log Mv =
1
α
(log ƞInt - log K)
log Mv =
1
0.76
(log 0.79- log 2X10-4)
log Mv = 1.3158 (log 0.79 - log 0.0002)
log Mv = 1.3158[-0.1024- (-3.690)]
log Mv = 1.3158[3.690 -0.1024]
log Mv = 1.3158 [3.5876]
log Mv =4.7206
Mv = a.log(4.7206)
Mv = 52,553 g/mol
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.25 0.5 0.75 1
Ƞsp/C
Concentration (%)
ƞInt = 0.79

12. Results
• Intrinsic Viscosity ƞInt = 0.79
• Molecular weight of a high polymer PVA = 52,553 g/mol

13. Experimental Video
https://www.youtube.com/watch?v=68bo-h3Kf7s

14. Theory
• When the number of repeating unit i.e. No. of monomers in the polymer is in excess of
100 , the polymer molecule is called High Polymer.
• Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer.
• It is having the general formula [CH2CH(OH)]n.
Polymerisation
n(CH2=CHOH)
Polyvinyl alcohol (Polymer)
• It is colorless (white) and odorless. It is commonly supplied as beads.
• Generally 1% PVA solution (Stock solution) is prepared by dissolving 1 g of solid powder
PVA in 50 mL distilled water by boiling and diluting the solution at room temperature to
100 mL.
Vinyl alcohol
(monomer)

15. Theory (Continued----)
• In this method the viscosity of PVA polymer sample is determined by comparing its
viscosity with a standard solvent like water whose viscosity is known (1 centipoise).
• With increase in concentration of polymer solution from 0.10% to 1.00%, the viscosity of
the polymer solution also increases.
• The increase in viscosity with concentration of the polymer solution is reflected from the
efflux time which also increases with rise in concentration.
• The relative viscosity (ƞrel) for different polymer solutions is calculated by the formula
ƞrel =
𝑒𝑓𝑓𝑙𝑢𝑥 𝑡𝑖𝑚𝑒 𝑓𝑜𝑟 𝑝𝑜𝑙𝑦𝑚𝑒𝑟 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑜𝑓 𝑎 𝑔𝑖𝑣𝑒𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
𝑒𝑓𝑓𝑙𝑢𝑥 𝑡𝑖𝑚𝑒 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑤𝑎𝑡𝑒𝑟 (𝑡𝑠)
------ (1)
• From the calculated values of relative viscosity (ƞrel), specific viscosity (ƞsp) is calculated for
each polymer solution using equation
ƞsp = ƞrel – 1 -------- (2)

16. Theory (Continued----)
• The ratio Ƞsp/C indicate relative increase in specific viscosity per unit concentration of
polymer.
• It is also known as reduced viscosity.
• It depends upon the concentration of a polymer solution.
• Therefore the plot Ƞsp/C against concentration is extrapolated to zero concentration.
• This extrapolated value is known as intrinsic viscosity (ƞInt) which is also called viscosity
number or Staudinger index.
ƞInt = C0
𝑙𝑖𝑚 Ƞsp
𝐶
----------- (3)
• The viscosity average molecular weight is calculated from the experimentally measured
intrinsic viscosity (ƞInt) value using Mark Houwink equation
ƞInt = K.Mv
α ------------ (4)
Here α = 0.76 K = 2x10-4 are the constants for a given PVA polymer solution.