Chemistry Lab: Determination of the
Universal Gas Constant (R)
You will be collecting butane gas (C4H10) using the “over water” method described in class. By
determining the initial and final mass of the lighter, you will be able to calculate the number of moles
of gas captured. Through Dalton’s Law of Partial Pressures, you will calculate the pressure of butane
gas. Using this, and the measured values for temperature and volume, you will be able to use the Ideal
Gas Law to calculate an experimental value for R, the Universal Gas Constant.
Purpose:
1. To measure the volume, pressure, moles, and temperature of a sample of wet butane gas
2. To determine the pressure of dry butane gas by using Dalton’s Law of Partial Pressures
3. To calculate the experimental value of the Universal Gas Constant, R, and compare it with
the accepted value
Materials:
Balance
100-ml Graduated cylinder Hair Dryer
Thermometer
Butane lighter
Fume Hood
Pneumatic trough
Barometer
Procedure:
1. Put on your lab apron and safety goggles.
2. Record the mass of the dry butane lighter in Table 1. Be sure not to let any gas out of the
lighter after finding its initial mass.
3. Record the temperature of the water in the pneumatic trough in Table 1.
4. Invert and fill with water a 100 ml graduated cylinder in the pneumatic trough, being sure
not to have any air bubbles in the graduated cylinder.
5. While one partner holds the mouth of the graduated cylinder under the surface of the water,
the other partner should hold the butane lighter under water, releasing the gas into the
graduated cylinder. Continue collecting the gas until 100 ml of water is displaced. When
you measure the volume, be sure that the water level inside the graduated cylinder is
the same as the water level in the trough. Record the volume of gas captured in Table 1.
6. Remove the lighter from the water and dry it with a hairdryer. Be sure to get the lighter
COMPLETELY DRY!! ALSO, be sure not to let any gas out of the lighter in the process.
Once it is dry, record the mass in Table 1.
7. Record the barometric pressure of the room in Table 1.
8. Use the chart to record the vapor pressure of water (PH2O) at room temperature in Table 1.
9. Remove the graduated cylinder from the trough. Turn it upright and cover the top with a
watch glass. Proper disposal of the heavier than air butane involves pouring it out in the
operating fume hood.
Data Presentation:
TABLE 1. Collected Data
Initial mass of butane lighter
______________ g
Final mass of butane lighter
______________ g
Temperature of water
__________ ˚C
Volume of gas collected
___________mL
Barometric pressure of room Pt
__________ atm
Vapor pressure of water at room temperature(PH2O) __________ atm
Data Analysis: Find the variables to plug into the Ideal Gas Law.
1. Record the difference in the mass of the lighter in Table 2.
2. Using the difference in the mass of the lighter, calculate the number of moles (n) of butane
gas collected. Butane’s formula is C4H10. This value is the (n) in step 6.
3. Using Dalton’s Law of partial pressures Pt = PH2O + Pb, determine the pressure of butane gas
(Pb). Pt = barometric pressure, PH2O = Vapor pressure of water at room temperature. Solving
for Pb will yield the pressure of butane gas. This value is the (P) in step 6.
4. Convert the temperature of water from Table 1 into Kelvins and record it in Table 2.
5. Convert the volume of gas collected from Table 1 into liters and record it in Table 2.
6. Using the Ideal Gas Law (PV = nRT), calculate the experimental value of R, the universal
gas constant. Record this value in Table 2. Also record the accepted value of R in Table 2.
7. Calculate the percent error by dividing the absolute value of the difference between the
experimental and accepted R values by the accepted R value and multiplying by 100.
Record this value in Table 2.
% error = /experimental R – accepted R/ X 100
accepted R
8. Show ALL calculations in a neat and organized fashion. It is acceptable to type in the
calculations or include an appendix of hand written calculations.
TABLE 2. Calculated Data
Mass difference of butane lighter
__________ g
Moles of butane gas (C4H10) collected
(n)
__________ moles C4H10
Partial pressure of butane gas C4H10 (Pb)
(P)
__________ atm
Converted temperature of water
(T)
__________K
Converted volume of gas collected
(V)
__________L
Experimental value of R
__________ Latm/molK
Accepted value of R
__________ Latm/molK
Percent error in your value of R
__________ %
Conclusions:
1. List at least 3 factors that either did or could contribute to the percent error?
2. Would the value of R go up or down if the gas had not been corrected for the partial
pressure of water? Why?
3. How could this experiment be repeated to increase the accuracy, or in other words, decrease
the percent error?
4. Why is it said that the R value is “accepted”? Is this really the value, or is it some other
value?
5. What is the difference between a scientific law and a legal law?