Density viscosity Chemical Engineering Notes | EduRev

Chemical Engineering : Density viscosity Chemical Engineering Notes | EduRev

 Page 1


University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
OBJECTIVE: 
To measure the density of water at room temperature and hence find its viscosity, using two 
standard liquids and an Ostwald viscometer. 
 
THEORY: 
The density of fluids changes with temperature and is not fixed. But certain fluids are chosen 
as standards as there is not a large change in the value of density. Using these, the densities of 
other fluids can be calculated. 
The viscosity of fluid is a measure of the resistance of the fluid which is being deformed by 
either shear stress or tensile stress. In everyday terms (for fluids), viscosity is usually known 
as ‘internal friction’. Thus, water is ‘thin’, having a lower viscosity, while honey is ‘thick’, 
having a higher viscosity. Viscosity describes a fluid's internal resistance to flow and may be 
thought of as a measure of fluid friction. In Ostwald’s Viscometer, when a liquid flows by 
gravity, the time taken by the liquid to flow between the two marks, upper and lower marks, 
through a vertical capillary tube is determined. The time of flow of the liquid under test is 
compared with the time taken by the two standard liquids. The viscosity of the unknown 
liquid can be determined using the equation: 
?/? = At – B/t
2 
 
 
DESCRIPTION OF SETUP: 
The Ostwald viscometer is a type of capillary viscometer. There is a U shaped tube consisting 
of two bulbs and two marks. The Ostwald viscometer is also known as the U-
tube viscometer or the capillary viscometer. This device measures the fluid’s viscosity using 
direct or reverse flow of the test fluid through a U-shaped tube. 
The Ostwald viscometer measurement is determined by noting the time required for the fluid 
to flow a certain distance through tubing of a specific diameter. Each side of 
an Ostwald viscometer consists of different size of tubing. Capillary is a small tube with a 
very small cross sectional area. For a direct flow viscometer, a bulb is located toward the top 
of the capillary side. On the wider diameter side, a slightly larger bulb is located toward the 
bottom. Two marks are placed on the tubing at a known distance apart. These marks are 
placed above and below the smaller bulb. 
 
 
 
 
 
 
 
Page 2


University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
OBJECTIVE: 
To measure the density of water at room temperature and hence find its viscosity, using two 
standard liquids and an Ostwald viscometer. 
 
THEORY: 
The density of fluids changes with temperature and is not fixed. But certain fluids are chosen 
as standards as there is not a large change in the value of density. Using these, the densities of 
other fluids can be calculated. 
The viscosity of fluid is a measure of the resistance of the fluid which is being deformed by 
either shear stress or tensile stress. In everyday terms (for fluids), viscosity is usually known 
as ‘internal friction’. Thus, water is ‘thin’, having a lower viscosity, while honey is ‘thick’, 
having a higher viscosity. Viscosity describes a fluid's internal resistance to flow and may be 
thought of as a measure of fluid friction. In Ostwald’s Viscometer, when a liquid flows by 
gravity, the time taken by the liquid to flow between the two marks, upper and lower marks, 
through a vertical capillary tube is determined. The time of flow of the liquid under test is 
compared with the time taken by the two standard liquids. The viscosity of the unknown 
liquid can be determined using the equation: 
?/? = At – B/t
2 
 
 
DESCRIPTION OF SETUP: 
The Ostwald viscometer is a type of capillary viscometer. There is a U shaped tube consisting 
of two bulbs and two marks. The Ostwald viscometer is also known as the U-
tube viscometer or the capillary viscometer. This device measures the fluid’s viscosity using 
direct or reverse flow of the test fluid through a U-shaped tube. 
The Ostwald viscometer measurement is determined by noting the time required for the fluid 
to flow a certain distance through tubing of a specific diameter. Each side of 
an Ostwald viscometer consists of different size of tubing. Capillary is a small tube with a 
very small cross sectional area. For a direct flow viscometer, a bulb is located toward the top 
of the capillary side. On the wider diameter side, a slightly larger bulb is located toward the 
bottom. Two marks are placed on the tubing at a known distance apart. These marks are 
placed above and below the smaller bulb. 
 
 
 
 
 
 
 
University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
 
SCHEMATIC DIAGRAM: 
 
 
 
 
 
 
 
 
 
 
 
 
 
PROCEDURE: 
(i). The room temperature was noted down and the specific gravity bottle was calibrated 
using mercury at room temperature. 
(ii). The density of water was calculated using the specific gravity bottle. 
(iii). The viscometer was installed in a vertical position and was checked for any type of 
leakage. 
(iv). A standard liquid was taken, say ethyl acetate, whose viscosity is known at given 
temperature and was used to fill the viscometer. 
(v). Then, the pinch knob was opened and the time required by the liquid to pass between 
the two marks, at the top and bottom of the bulb, was measured. 
(vi). The above steps were repeated to get around 8 readings for the given liquid. 
(vii). Another set of 8 readings was taken for the second standard liquid i.e. heptane. 
(viii). The calculations were carried out and the viscosity of water determined. 
 
Page 3


University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
OBJECTIVE: 
To measure the density of water at room temperature and hence find its viscosity, using two 
standard liquids and an Ostwald viscometer. 
 
THEORY: 
The density of fluids changes with temperature and is not fixed. But certain fluids are chosen 
as standards as there is not a large change in the value of density. Using these, the densities of 
other fluids can be calculated. 
The viscosity of fluid is a measure of the resistance of the fluid which is being deformed by 
either shear stress or tensile stress. In everyday terms (for fluids), viscosity is usually known 
as ‘internal friction’. Thus, water is ‘thin’, having a lower viscosity, while honey is ‘thick’, 
having a higher viscosity. Viscosity describes a fluid's internal resistance to flow and may be 
thought of as a measure of fluid friction. In Ostwald’s Viscometer, when a liquid flows by 
gravity, the time taken by the liquid to flow between the two marks, upper and lower marks, 
through a vertical capillary tube is determined. The time of flow of the liquid under test is 
compared with the time taken by the two standard liquids. The viscosity of the unknown 
liquid can be determined using the equation: 
?/? = At – B/t
2 
 
 
DESCRIPTION OF SETUP: 
The Ostwald viscometer is a type of capillary viscometer. There is a U shaped tube consisting 
of two bulbs and two marks. The Ostwald viscometer is also known as the U-
tube viscometer or the capillary viscometer. This device measures the fluid’s viscosity using 
direct or reverse flow of the test fluid through a U-shaped tube. 
The Ostwald viscometer measurement is determined by noting the time required for the fluid 
to flow a certain distance through tubing of a specific diameter. Each side of 
an Ostwald viscometer consists of different size of tubing. Capillary is a small tube with a 
very small cross sectional area. For a direct flow viscometer, a bulb is located toward the top 
of the capillary side. On the wider diameter side, a slightly larger bulb is located toward the 
bottom. Two marks are placed on the tubing at a known distance apart. These marks are 
placed above and below the smaller bulb. 
 
 
 
 
 
 
 
University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
 
SCHEMATIC DIAGRAM: 
 
 
 
 
 
 
 
 
 
 
 
 
 
PROCEDURE: 
(i). The room temperature was noted down and the specific gravity bottle was calibrated 
using mercury at room temperature. 
(ii). The density of water was calculated using the specific gravity bottle. 
(iii). The viscometer was installed in a vertical position and was checked for any type of 
leakage. 
(iv). A standard liquid was taken, say ethyl acetate, whose viscosity is known at given 
temperature and was used to fill the viscometer. 
(v). Then, the pinch knob was opened and the time required by the liquid to pass between 
the two marks, at the top and bottom of the bulb, was measured. 
(vi). The above steps were repeated to get around 8 readings for the given liquid. 
(vii). Another set of 8 readings was taken for the second standard liquid i.e. heptane. 
(viii). The calculations were carried out and the viscosity of water determined. 
 
University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
RECORDINGS: 
Room temperature                                            = 29 °C 
Temperature of water                                       = 28.5 °C 
Weight of empty specific gravity bottle           = 17.97 g 
Weight of specific gravity bottle + mercury    = 166.82 g  
Weight of specific gravity bottle + water         = 28.92 g 
Density of Hg                                                   =13521.36 kg/m
3
 
Density of ethyl acetate                                    = 897 kg/m
3
 
Density of heptane                                            = 671 kg/m
3
 
Viscosity of ethyl acetate                                  = 0.426 centiPoise 
Viscosity of heptane                                          = 0.376 centiPoise 
 
OBSERVATIONS: 
Efflux time in seconds (s) 
S. No. Ethyl Acetate Heptane Water 
1 9.09 9.45 9.36 
2 9.18 9.54 9.49 
3 9.21 9.47 9.36 
4 9.31 9.67 9.45 
5 9.26 9.49 9.42 
6 9.22 9.46 9.48 
7 9.15 9.52 9.37 
8 9.18 9.57 9.40 
Average 9.2 9.52 9.42 
 
SAMPLE CALCULATIONS: 
Volume of specific gravity bottle = Weight of mercury/Density of mercury 
                     = (148.85/13.522) cm
3
 
                                                      = 11.01 cm
3
 
Weight of water = (28.92 – 17.97) g = 10.95 g 
Calculated density of water = Weight of water/Volume of bottle 
                                             = (10.95/11.01)g/cm
3
 = 0.99484 g/cm
3 
 Thus,                         ?
water
 = 994.836 kg/m
3
 
Page 4


University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
OBJECTIVE: 
To measure the density of water at room temperature and hence find its viscosity, using two 
standard liquids and an Ostwald viscometer. 
 
THEORY: 
The density of fluids changes with temperature and is not fixed. But certain fluids are chosen 
as standards as there is not a large change in the value of density. Using these, the densities of 
other fluids can be calculated. 
The viscosity of fluid is a measure of the resistance of the fluid which is being deformed by 
either shear stress or tensile stress. In everyday terms (for fluids), viscosity is usually known 
as ‘internal friction’. Thus, water is ‘thin’, having a lower viscosity, while honey is ‘thick’, 
having a higher viscosity. Viscosity describes a fluid's internal resistance to flow and may be 
thought of as a measure of fluid friction. In Ostwald’s Viscometer, when a liquid flows by 
gravity, the time taken by the liquid to flow between the two marks, upper and lower marks, 
through a vertical capillary tube is determined. The time of flow of the liquid under test is 
compared with the time taken by the two standard liquids. The viscosity of the unknown 
liquid can be determined using the equation: 
?/? = At – B/t
2 
 
 
DESCRIPTION OF SETUP: 
The Ostwald viscometer is a type of capillary viscometer. There is a U shaped tube consisting 
of two bulbs and two marks. The Ostwald viscometer is also known as the U-
tube viscometer or the capillary viscometer. This device measures the fluid’s viscosity using 
direct or reverse flow of the test fluid through a U-shaped tube. 
The Ostwald viscometer measurement is determined by noting the time required for the fluid 
to flow a certain distance through tubing of a specific diameter. Each side of 
an Ostwald viscometer consists of different size of tubing. Capillary is a small tube with a 
very small cross sectional area. For a direct flow viscometer, a bulb is located toward the top 
of the capillary side. On the wider diameter side, a slightly larger bulb is located toward the 
bottom. Two marks are placed on the tubing at a known distance apart. These marks are 
placed above and below the smaller bulb. 
 
 
 
 
 
 
 
University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
 
SCHEMATIC DIAGRAM: 
 
 
 
 
 
 
 
 
 
 
 
 
 
PROCEDURE: 
(i). The room temperature was noted down and the specific gravity bottle was calibrated 
using mercury at room temperature. 
(ii). The density of water was calculated using the specific gravity bottle. 
(iii). The viscometer was installed in a vertical position and was checked for any type of 
leakage. 
(iv). A standard liquid was taken, say ethyl acetate, whose viscosity is known at given 
temperature and was used to fill the viscometer. 
(v). Then, the pinch knob was opened and the time required by the liquid to pass between 
the two marks, at the top and bottom of the bulb, was measured. 
(vi). The above steps were repeated to get around 8 readings for the given liquid. 
(vii). Another set of 8 readings was taken for the second standard liquid i.e. heptane. 
(viii). The calculations were carried out and the viscosity of water determined. 
 
University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
RECORDINGS: 
Room temperature                                            = 29 °C 
Temperature of water                                       = 28.5 °C 
Weight of empty specific gravity bottle           = 17.97 g 
Weight of specific gravity bottle + mercury    = 166.82 g  
Weight of specific gravity bottle + water         = 28.92 g 
Density of Hg                                                   =13521.36 kg/m
3
 
Density of ethyl acetate                                    = 897 kg/m
3
 
Density of heptane                                            = 671 kg/m
3
 
Viscosity of ethyl acetate                                  = 0.426 centiPoise 
Viscosity of heptane                                          = 0.376 centiPoise 
 
OBSERVATIONS: 
Efflux time in seconds (s) 
S. No. Ethyl Acetate Heptane Water 
1 9.09 9.45 9.36 
2 9.18 9.54 9.49 
3 9.21 9.47 9.36 
4 9.31 9.67 9.45 
5 9.26 9.49 9.42 
6 9.22 9.46 9.48 
7 9.15 9.52 9.37 
8 9.18 9.57 9.40 
Average 9.2 9.52 9.42 
 
SAMPLE CALCULATIONS: 
Volume of specific gravity bottle = Weight of mercury/Density of mercury 
                     = (148.85/13.522) cm
3
 
                                                      = 11.01 cm
3
 
Weight of water = (28.92 – 17.97) g = 10.95 g 
Calculated density of water = Weight of water/Volume of bottle 
                                             = (10.95/11.01)g/cm
3
 = 0.99484 g/cm
3 
 Thus,                         ?
water
 = 994.836 kg/m
3
 
University Institute of Chemical Engineering and Technology, P.U. Chandigarh 
 
Equation used to find density:  
?/ ? = At – B/t
2 
 
For ethyl acetate: 
                                0.000426/897 = A (9.2) – B/(9.2)
2 
For heptane: 
                               0.00055/671 = A (9.52) – B/(9.52)
2
  
Therefore;   A= 1.244×10
-7
         B = 5.658×10
-5 
For water:        
 
?/995.95 = (1.244×10
-7
) × (9.42) - (5.658×10
-5
)/(9.42)
2
 
? 
water 
= 0.631 centiPoise 
 
DISCUSSION OF RESULTS: 
Value of ?water found experimentally              = 0.631 centiPoise 
Theoretical value of ?water from the literature = 0.798 centiPoise 
Percentage Error = [(0.798 – 0.631)/(0.798)] ×100 
                             = 20.8 % 
Value of ?water found experimentally              = 994.839 kg/m
3
 
Theoretical value of ?water from the literature = 995.948 kg/m
3
 
Percentage Error = [(995.839 – 995.948)/(995.948)] ×100  
                             = 0.111 % 
The errors in the results can be attributed to various reasons. Experimental error is another 
cause and human error is a major reason for the inaccurate results. Also, the weighing 
balance cannot be totally relied upon. 
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