Viscosities of Liquids

Topics: Viscosity, Fluid dynamics, Fluid Pages: 7 (1259 words) Published: February 12, 2013
Lab report: Viscosity of Liquids

Introduction
This experiment focuses on measurements of different trials of various concentrations. The collected data is used to compare and contrast to the ideal binary solutions and their components. The Ostwald viscometer is a useful laboratory equipment to measure the viscosities of many binary solutions. Background

Molecules have the ability to slide around each other, result in a flow. Such a flow has a resistance called viscosity. Microscopically, viscosity is the energy association of molecules in a liquid state. The energy needs to be applied to overcome the attractive forces between the molecules in order for the liquid to flow. The heat of vaporization or surface tensions are examples of attractive forces.

This is the Newton’s law of viscous flow:
dfx / dA = η (∂vx /∂z)z
Fluids that behave like the equation above are called Newtonian fluids or they go laminar flow.
Viscosity coefficient η =kg m-1 s-1

Viscosity measurement is important in many applications. This property of the fluid can be used to determine the rate of mass transport, diffusion or within that liquid when it is to be used as a solvent. These are all fundamental and intrinsic property of a liquid. Mass transport through a circular tube of small internal diameter by Poiseuille:

dV / dt = π r4 ΔP / 8 η L
dV/dt = volume flow rate of liquid
r = radius of the tube
L = length of the tube
ΔP = change in pressure, also the driving force
F = 1 / η
F = fluidity, denotes fluid mobility which is one that has a relatively low viscosity F = xA F’A + xB F’B

When we have mixed solutions of non- associating liquids (additive), we can apply the above equation to find the flow of liquid upon chemical composition of that liquid. Ideal solution is one in which the interaction energies between its constituents are the same as those between the molecules of each pure components.

Non ideal solution has the formation of association complexes between the components occurs, or the destruction of such complexes originally present in pure liquids happens upon mixing. For this, F = xA F’A + xB F’b does not hold.

For the experiment, the Oswald viscometer is to be used to measure data:

η = π r4 P t / 8 V L
t = time elapsed
v = volume of liquid (constant)
p = density
Data/Results
Temperature: 24C
Calibration time of water (in min)
T1: 1.50
T2: 1.50
T3: 1.50
Pressure: 29.62 inches of mercury
Table 1: Methanol/water times (min) and concentrations (ml/ml) Methanol/water| 20%| 40%| 60%| 80%| 100%|
T1| 2.46| 2.27| 3.24| 3.12| 1.28|
T2| 2.49| 2.35| 3.26| 3.30| 1.28|
T3| 2.50| 2.40| 3.28| 3.50| 1.28|

Table 2: Toluene/p-xylene times (min) and concentrations (ml/ml) Toluene/pxylene| 0%| 20%| 40%| 60%| 80%| 100%|
T1| 1.17| 1.18| 1.19| 1.18| 1.22| 1.23|
T2| 1.17| 1.18| 1.20| 1.18| 1.22| 1.24|
T3| 1.17| 1.19| 1.20| 1.18| 1.22| 1.24|

Table 3: Flow chart of viscosities (methanol/water)
(not shown) Pr*Tr = 1.5 (P water = 1gmL-1, T water = 1.5min) Nr = 0.89centipoise
Viscosity of methanol (centipoise) = (P*t/Pr*tr)*Nr
| Trial| t (min)| P of methanol/water (g/ml)| p*t| Viscosity of methanol (centipoise)| 20%| 1| 2.46| 0.971| 2.38866| 1.4172716|
| 2| 2.49| 0.971| 2.41779| 1.4345554|
| 3| 2.5| 0.971| 2.4275| 1.440316667|
|  |  |  |  |  |
40%| 1| 2.27| 0.944| 2.14288| 1.271442133|
| 2| 2.35| 0.944| 2.2184| 1.316250667|
| 3| 2.4| 0.944| 2.2656| 1.344256|
|  |  |  |  |  |
60%| 1| 3.24| 0.909| 2.94516| 1.7474616|
| 2| 3.26| 0.909| 2.96334| 1.7582484|
| 3| 3.28| 0.909| 2.98152| 1.7690352|
|  |  |  |  |  |
80%| 1| 3.12| 0.859| 2.68008| 1.5901808|
| 2| 3.3| 0.859| 2.8347| 1.681922|
| 3| 3.5| 0.859| 3.0065| 1.783856667|
|  |  |  |  |  |
100%| 1| 1.28| 0.788| 1.00864| 0.598459733|
| 2|...