Investigation to determine the viscosity of glycerol Essay
Investigation to determine the viscosity of glycerol
This document reports on an experiment that examined the relationship between temperature and viscosity. The terminal velocity and up-thrust experienced by a sphere of fixed weight and radius was calculated by dropping it into a measuring cylinder filled with glycerol heated to different temperatures. Using Stokes Law viscosity corresponding to each temperature level was worked out. This generated a range of data points with viscosity corresponding to each temperature level.
These data points were statistically analysed. The results corresponded to those indicated by theory i. e. temperature and viscosity are inversely related; as temperature increased viscosity decreased. This report is in five sections. The first details the plan and the science on which the experiment is based. The second describes implementation while the third analyses the results. The fourth section evaluates the both the experiment and its results. The fifth concludes. 1 Plan 1. 1 The Question Is viscosity affected by temperature? When temperature increases does viscosity decrease or increase and if it does are the changes systematic or random? These are the questions I investigate in this experiment. 1. 2 Key Concepts Archimedes’ principle
“A body immersed in a fluid (totally or partially) experiences an upthrust (i. e. an apparent loss of weight) which is equal to the weight of fluid displaced. ” 1Ships don’t sink in water because of upthrust. Upthrust is also the cause for weight loss when a body is partially or wholly immersed in a fluid. Viscosity “Viscosity is the virtue by which a fluid offers a resistance to the motion through it of any solid body. “2 The theory of viscosity is almost identical to the theory of friction between two solids, just that viscosity is the term used for fluids. Viscosity is basically the resistance between the particles within a fluid.
In a solid molecules are tightly packed i. e. there is a strong intermolecular force. Therefore when you move a solid, it moves as a whole as all the particles move together. In a fluid this is not the case. This is because due to lower intermolecular force the particles move at different velocities in relation to each other. This feature can be understood by discussing what happens when pouring a jug of water into a glass. In liquids the molecules flow in layers. See the right – water flowing from a jug, it looks simple, but in reality it is quite complex. Actually only the top layer of water is flowing, the bottom layer is still.
This is explained with the help of the diagram on the left. The red line is the upper layer of water in the jug which flows in the glass, when this layer has flown into the glass the maroon layer starts flowing and the finally the black layer. This is because the black layer is closest to the solid (which in this case is the jug); the resistance offered by the solid is greater than the resistance offered by the layers of the liquid. This is because the number of molecules that make contact between the solid and the liquid layer are more than those that make contact between the liquid and liquid layer.
The number of molecules that have contact between the liquid layer and air is the least. Hydrogen Bonding “Unusually strong dipole-dipole attractions that occur among molecules in which hydrogen is bonded to a highly electronegative atom. “3 Hydrogen bonding is a much stronger variant of Van Der Waals Forces. This strong bonding causes great friction between the layers of liquid and therefore gives glycerol its property of high viscosity. Glycerol has a high viscosity as opposed to other alcohols because, it has three -OH functional groups attached to it.
Therefore more hydrogen bonds are formed, thus increasing the attraction between two neighbouring molecules (greater bond strength). Thus unlike alcohols that are volatile, glycerol is not only non-volatile, but is also very thick and viscous. Stokes Law Stokes Law plays an important part in understanding the motion of a solid (in his experiment he used a sphere) through liquids. “Stokes law states that when a body is under free fall in a tube containing a liquid of infinite length there is a point when there is no more acceleration in the body and the body reaches terminal velocity.
Stoke further went on to say that this was due to the viscous forces acting within the liquid. The layers of the liquid in contact with the solid start moving with the velocity of the solid particle whereas the layers far away from the body remain at rest. The viscous forces being frictional forces act against the acceleration of the body and therefore there is a point when the viscous forces equal the resultant force driving the body. This is when the body reaches its terminal velocity.
University/College: University of Chicago
Type of paper: Thesis/Dissertation Chapter
Date: 7 July 2017
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