The Effect of Hydrogen Bonding on Resisting Flow
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THE EFFECT OF HYDROGEN BONDING
ON REGISTING FLOW
Design
Investigating a factor affecting the viscosity of a mixture of liquid
Research Question
Look at the issue given to you and identify a focused research question. For example, “The effect of changing charge flowing on the mass of copper deposited on the cathode in an electrolytic cell containing 1 mol dm−3 copper(II) sulfate.” is better than “The effect of size of current in an electrolytic cell on the mass of metal deposited on the cathode.”
Background Theory
Viscosity is the resistance of a fluid to flow, either within itself, or to moving past an objects moving through it. A liquid with high viscosity is thick and flows slowly. A liquid with a low viscosity is thin and flows quickly. Different liquids have different viscosities.
Factors, which affect viscosity of a liquid, are:
Size of a molecule: Spherical molecules provide less resistance therefore less viscosity compared to oval shaped or disc-like molecule which provide a greater resistance in the flow of liquid. The more spherical molecule is, the lower the viscosity of a liquid.
Temperature: When a solid or liquid is heated, most of the bonds are being broken between particles. In viscosity, the bonds are closer together and they resists the flow, so when the liquid is heated, the bonds are being broken. The liquids with broken bonds flow faster than before.
Intermolecular force: There are three types of intermolecular force between molecules: hydrogen bonding, van der Waals forces and permanent dipole force. Hydrogen bonding is the strongest bond in terms of intermolecular forces. The attraction between molecules is high; the viscosity of a liquid is high.
In this investigation, the purpose is to compare the viscosities of four different liquids and to interpret the results in terms of hydrogen bonding.
Hypothesis
The liquids, which have more hydrogen bonding will have higher viscosity and flow slowly.
Test a liquids viscosity by timing how long it takes for the marble to sink.
Variables
Clearly state:
Independent variable
The one which you purposely vary, eg surface area.
If you are going to plot a graph of your data, this variable will go on the x-axis.
Dependent variable
The one that is observed to see how it responds to the change made to the independent
variable, eg rate of reaction.
If you are going to plot a graph of your data, this variable will go on the y-axis.
Controlled variables
All other variables you must keep constant, eg concentrations, volumes, temperatures.
In this section you need to discuss and show your understanding of the need to control
variables and how they can affect results. NOTE that some variables cannot be realistically
controlled (eg room temperature) but should be monitored. Examiners have mentioned that in
the control of variables students rarely allow time for a variable such as temperature to
equilibrate.
You can present your controlled variables in the form of a table:
Variable controlled
Why it needs to be controlled
How it will be controlled
NB: Control variables are different from a control experiment!
Materials
List apparatus and solutions.
State quantities, eg 6 test tubes
State sizes, eg 50 cm3 measuring cylinders.
State concentrations and volumes, eg 100 cm3, 1 mol dm−3 hydrochloric acid solution (dont forget to allow for gross errors).
You can present your materials in the form of a table:
Chemicals/Consumables
Glassware
Equipment
Risk Assessments
State safety issues/identify hazards and how will you minimise them.
Use MSDS on the chemicals to state hazards/risks associated with their use, precautions that should be taken and how wastes are to be disposed of. This can be presented as a table:
Chemical
Hazards/Risks
Precautions
First