Controlled variables: the type of gas in the flask is kept the same and the rubber bung was never removed from the flask once the experiment had been started. The volume of the gas sample and the number of molecules it contains is kept constant.
Materials and Methods:
Diagram of Setup:
Apparatus: pressure sensor, temperature probe, flask with rubber bung, water bath (large beaker), ice blocks, hot water from kettle.
Procedure: First, the pressure in the flask will be measured at room temperature and then the flask will be placed in a water bath so the temperature of the bath can be increased by small increments to determine the effect of temperature on vapour pressure. The natural log of the vapour Pressure (in kPa) versus the Kelvin temperature is plotted.
1. The apparatus for this experiment is set up as shown in the diagram above.
2. The flask and temperature probe are completely immersed into the hot-water bath (as shown in the diagram). (The flask will be buoyant and may need to held down).
3. After a few minutes the temperature and pressure are recorded.
4. The independent variable is varied by cooling the hot water. To obtain a wide range of temperatures, ice is added to the water. The temperature of the water is kept constant for a few minutes before taking each result because air is a bad conductor of heat (insulator) and takes a longer time than liquids and solids to conduct heat from the water bath that it is in.
5. After every 3 minutes an ice block is added to the mixture to cool it down gradually, and the readings of temperature and pressure are taken simultaneously.
Methods for control of variables:
How the independent variable was varied: by adding an ice block to the hot water-bath to cool it down at a faster rate and obtain a wide range of readings.
How the controlled variables were controlled: a scale was used to ensure that the volume of gas was kept the same the same flask was used and the rubber bung was not removed throughout the experiment.
How sufficient relevant data recording was ensured: a wide range of readings were taken to maintain accuracy of the experiment.
Results:
Data collection:
Tables: Table showing the raw data collected:
Table showing processed data:
Equations and methods for collecting relevant data:
Sample calculation: temperature in degrees Celsius + 273 = temperature in Kelvin
For example (1st row of readings): 80.7 + 273=353.7
Data represented by graphs: both variables are continuous so a point graph is used
A Scatter diagram showing the same data with a line of best fit running through it:
Observations: the trend of the data shown is a straight line, and we see that as the water in the beaker cools down and also the temperature of the gas in the flask, the pressure decreases.
Conclusion
In the results obtained correspond with the hypothesis made. It has been proven that
a gas consists of molecules that are so small that they can be considered mass points and it is assumed that there are no forces between the mass points. The molecules are in constant motion and as they bounce off the walls of the container exert a pressure (a force per unit area) on the walls of the container. The average kinetic energy of the molecules is proportional to the temperature, and the higher the temperature the faster the molecules move. The pressure will increase as the temperature rises because the molecules move faster and hit the walls harder. Judging by the results obtained in this experiment, the pressure and temperature of the gas obey a linear relationship (as seen in the graph above). Compared to literature values the results obtained are similar in the sense that they all portray a linear relationship, which is, as temperature increases pressure increases and as temperature decreases, pressure decreases. the absolute temperature TK of the gas in Kelvin is proportional to the average kinetic energy of the gas molecules. So even though there are just as many gas molecules in the flask the pressure can be altered by heat.
“f molecules move faster, they will make more violent collisions (momentum) and they will arrive back at the wall for another bang more often. So you might expect the speed to appear twice over as a factor in the pressure. Pressure varies as (speed). A gas molecule's motion energy (KE) which clearly increases with temperature might be a good way of measuring temperature itself.”
Evaluation of procedures
- The pressure in the flask could have been slightly affected by body heat, as the flask is held into the water my hand, and this could further increase the kinetic energy of the gas molecules in the flask thus leading to an increase in pressure.
- The flask may not have fully conducted heat to equal that of the water-bath and the readings taken could have been different from that in the flask.
- The volume of water in the water-bath over the surface area of the flask could have increased or decreased some of the data obtained as parts of the flask could not be fully immersed in the water.
Improvements:
- Instead of holding the flask into the water-bath by hand, a clamp may be used to keep the flask in place
- The flask should be held in the flask for a longer time before taking temperature readings to allow the gas to conduct enough heat because air is a bad conductor of heat (insulator) and takes a longer time than liquids and solids to conduct heat from the water bath that it is in.
- The flask should be immersed in a constant depth of water so that the same surface area of the flask can be exposed to the water ensuring better conduction of heat.
References:
atmos.uiuc.edu
www.chm.davidson.edu/ChemistryApplets/GasLaws/CharlesLaw.html
school.discoveryeducation.com/lessonplans/programs/temperatureandpressure