Experiment n. 5 - Properties of gases

Experiment n. 5
Welcome chemists!
Here we are once more ready to share with you all a new experience!
This week, we studied how the pressure of a gas varies depending on the temperature at which it is subjected to.

Task
To study the pressure of a gas depending on the temperature at which it is subjected to.

Background information

According to Boyle’s law, we would have to double the pressure to halve the volume. Thus, if the volume of gas is to remain the same, doubling the temperature will require doubling the pressure.This law was first stated by the Frenchman Joseph Gay-Lussac (1778 to 1850). According to Gay-Lussac’s law, for a given amount of gas held at constant volume, the pressure is proportional to the absolute temperature.
Gay-Lussac’s Law is expressed as:


   So  P / T = k (constant).

where
Pi = initial pressure
Ti = initial absolute temperature
Pf = final pressure
Tf = final absolute temperature

It is extremely important to remember the temperatures are absolute temperatures measured in Kelvin, NOT °C or °F.

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Gay-Lussac-s-Law-952.html


Procedure
1. Collect the materials and arrange them following the image shown.
2. Pour water inside the container, so that it covers the gas container.
3. Connect the two sensors to the computer: the pressure sensor will be connected to the gas container and the temperature sensor will be inside the water.
4. Place some ice-cubes inside the water in order to cool down the temperature .
5. Turn on  the computer and open ‘Logger Pro’ program. Then, press ‘collect data’, in order to record the first values of temperature and pressure.
6. Then, switch the bunsen burner on to heat the water up. The temperature will start increasing, as the magnetic stirrer will homogenise the temperature of the water that consequently will homogenise the temperature of the gas at the same time and temperature.
7. Press ‘collect’ again, every time the temperature of the water increases about three degrees celsius. Proceed with this procedure until the temperature of the water reaches 100 ºC/273ºKelvin.
Materials:
- Magnetic stirrer with heating.
- Bunsen burner
- Container
- Schlenk
- Water
- Lighter
- Manometer- Tripod
- Clamp
- Stand
- A laptop with the programme “Logger Pro” installed, in order to record the data obtained.


VIDEOS AND IMAGES

Images of the materials used and the system created

Video: Practical explanation of Gay-Lussac's law using a balloon (well, rather a glove...)

Results: Graph and table

Table: Representing the pressure in hPa of a constant volume of gas in relation with its temperature in ºC.

Graph 1: Representing the pressure in hPa of a constant volume of gas in relation with its temperature in ºC. (original data)

Graph 2: Representing the pressure in hPa of a constant volume of gas in relation with its temperature in ºC (best fitting line)

Conclusion
After carrying out the experiment, and looking at the results recorded, we got to the conclusion that there is a directly proportional relationship between the pressure of a gas and the temperature it is subjected to, keeping the gas volume's constant, what proves Gay - Lussac’s law:

On the graph we can observe the following: R^2= 0,9974. In order for the experiment to be perfect, the number should be 1. But, although it is not exactly one, it is quite close. This means that our results are quite good.

It can be seen that the function represented is a lineal function.

In order to improve the results, as we had to collecr the data following a 'pattern of degrees' (we had to click on 'collect data' using the data processing program that we used everytime that the temperature increased a specific number of degrees celcius), and we sometimes commited errors, we should be more precise and careful when collecting the data.

On the other hand, we are happy to have used this new program and we consider it very appropriate and useful, as having such an interphase and sensor system connected to the computer which uses a data processing special program to collect the data, makes it a lot more easy to collect the data (which is collected more precisely) , and much quicker too. If we had done it by hand, the process would have been much longer, the fact that we would have had to draw a hand-made graph would have also made it slower and much less precise. And, by using 'Excell', we have even been able to calculate our error and to see how well or how wrong the experiment went.