Verification of Boyle’s Law
Introduction
Prior to this lab, Boyle’s Law was analyzed. Boyle’s law is an ideal gas law, stating that the pressure and volume of a gas have an inverse relationship. The law is valid, as long as the temperature and the amount of gas are constant. This experiment will demonstrate that as the independent variable (volume) increases, the dependent variable (pressure) decreases. This is tested by examining the pressure of gas in a syringe and measuring the pressure as the volume of gas in the syringe increases. By plotting the results it can be determined that there is a relation between these variables.
The equation for Boyle’s Law is PV = K. The P represents pressure which will be measured in kilopascals and the V represents volume which will be measured in millilitres. More specifically, for a given mass at a constant temperature, the pressure multiplied by the volume equals a constant (K). The constant, k, will depend on the number of moles and the temperature. Boyle’s law will hold if these two state functions are constant, meaning the k value will be a constant.
There are some limitations to Boyle’s Law that include the temperature at which the experiment is being performed. The temperature must remain constant because if there is variation in multiple factors, there is no way to prove Boyle’s Law. As stated before, the equation for Boyle’s Law that is being used to determine the constant is PV = K. This equation only has two variables, therefore only two factors in the experiment can change. One is controlled and the other will be observed. This should result in a constant value known as K because of the relationship between P and V.
Procedure:
The Gas Pressure Sensor was prepared by attaching a 20 mL syringe to the Sensor, that was connected to LabQuest 2.
The experiment begins with the volume of air measuring at 3 mL. The points were plotted once the pressure stabilized using LabQuest. After each point was plotted, the volume of air increased by 2 mL, making 9 plots on the graph (3mL- 19mL).
Any volume that was inputed had an additional 0.8 mL added on to consider the space inside the pressure sensor.
After the 9 measurements, the syringe was pushed back to the original volume of 3 mL.
All results were recorded in a table (see Data and Observations).
For specific steps regarding how to use LabQuest 2, refer to the Lab Manual.
Data and Observations:
Table 1: Data and Results when validating Boyle’s Law
Trial 1*
Independent Variable
Volume (mL)
Dependent variable
Pressure (kPa)
3.8
101.26
5.8
63.73
7.8
49.39
9.8
37.05
11.8
27.92
13.8
24.52
15.8
25.11
17.8
22.27
19.8
20.56
3.8
103.15
*Data was taken from table on LoggerPro. This explains why these values do not reflect the values on the raw data observations.
Table 2: Data and Results when validating Boyle’s Law
Trial Two
Independent Variable
Volume (mL)
Dependent variable
Pressure (kPa)
3.8
91.32
5.8
63.24
7.8
45.47
9.8
36.99
11.8
30.48
13.8
26.60
15.8
23.57
17.8
21.07
19.8
19.42
3.8
102.24
Table 3: Average Constant between Trial One and Two
Independent Variable
Average K
3.8
365.902
5.8
368.213
7.8
369.954
9.8
362.796
11.8
344.56
13.8
352.728
15.8
384.572
17.8
385.726
19.8
396.802
Observations: As expected, during the experiment we observed that as we increased the volume, the pressure decreased. This is shown on the graph; as the curve is decreasing.
Calculations
PV = K
P = pressure
V = volume
K = constant
PV=K
(101.26) (3.8)= K
384.788= K
Therefore the constant has a value of 3.8 x102 _____ when the volume is 3.8 mL and the pressure is 101.26 kPa.
Average K Value
K1 = constant from trial 1 at 3.8 mL
K2 = constant from trial 2 at 3.8 mL
KA= average constant
0.5 (K1 + K2 ) = KA
0.5 (384.788 + 347.016) = KA
365.902 = KA
Discussion
Sources of error
Human held syringe at the volume but it could have shifted
Similar to question 4
Trial 1 raw data was not recorded at the same time that graph was plotted (didn’t wait until it had stabilized)
First trial at 15.8 according to the graph the pressure increased instead of decreasing
During the lab there were encountered errors that potentially affected the data results. The data that was recorded on LabQuest was different than the raw data that was recorded when the pressure was being measured. This occurred because the data was recorded in the lab notebook before it was recorded on LabQuest. This also occurred because the pressure wasn’t stabilized when the results were measured. This could have also impacted why the constants were not all the same. Without any errors, this lab should have had different results. The dependent variable is where the error occurred. The constant should be the same, as the independent variable increases, the dependent variable should have decreased respectively, however the graphs show that the dependent variable is the reason that the constant was not the same.
Additionally, for trial one, there was an error in the pressure value when the volume was at 15.8mL. At 15.8 mL instead of seeing a pressure decrease compared to 13.8, the pressure increased. This was problematic because this pressure value did not reflect Boyle’s Law or the pattern of the rest of the data. Ultimately this was overlooked when the entire lab was being taken into account because this one increase was clearly an error, due to analyzing every other result, which showed a decrease in pressure, therefore validating Boyle’s Law.
Using your data, calculate a Boyle’s law constant. Explain how you determined the constant.
The Boyle’s Law constant is determined by multiplying the volume by the pressure. We determined the K value by multiplying a volume of 3.8 mL by a pressure of 101.26 kPa. This gave a constant of 3.8 x 102. Hypothetically, this constant would be the same for a given reaction, therefore if the independent variable continued to increase from the original value of 3.8mL, dividing the constant by the volume would give you the pressure at that desired volume.
Describe the mathematical relationship illustrated by Boyle’s law, and use the constant you calculated in Step 1 to write an equation for Boyle’s law.
The mathematical relationship is illustrated by measuring and multiplying the initial volume and the associated pressure, giving the Boyle’s constant. This number can be used to determine the pressure if you have the Boyle’s constant and the volume.
You were directed to take your first and last measurements at the same mark on the syringe. Speculate about the importance of taking multiple readings of the dependent variable for the same value of the independent variable.
When crafting a hypothesis, it is important to take multiple readings of the dependant variable for the same value of the independent variable, because by doing so you will increase the accuracy of the data and will avoid reporting false or feasible results.
Boyle’s law requires certain conditions be met for other gas variables. What are these variables? Did you take these variables into consideration? What did you do to ensure they remained constant? Does this affect your results? If so, how? If not, why not?
Pressure and volume are the two variables identified in Boyle’s Law. There are other conditions that were not considered in this lab that could have affected the results. These conditions include but are not limited to, the temperature at which the experiment was performed at, the number of moles of the gas itself, and the time it took for each different pressure to be recorded. The temperature was assumed to have remained constant because the lab was performed over a short period of time and was indoors, therefore any temperature change outside would not have affected the reaction. The number of moles of the gas was something that was uncontrolled, however the system used to measure the reaction was closed, therefore gas could not have escaped nor could it have been added. This could have affected why the constants were not the same for each separate measurement of K. These were not the only factors that affected the value of K but they would have impacted the different values that were recorded.
Use Logger Pro (software link available on Brightspace) to make all graphs.
Conclusion
According to the data, as the volume increased the pressure decreased, proving the inverse relationship between these two variables.
Need Assessment Criteria
One example of each different calculation
Raw data after references
mzidan@uottawa.ca
Any tense that is consistent
Different k value, you can find k in a different manor
Explain observations in discussion