Determination of Determination of the Molecular the Molecular

Weight of ButaneWeight of Butane

Virtual LabVirtual Lab

Objectives of this lab:Objectives of this lab:

1.1. Collect a sample of gas using the Collect a sample of gas using the water displacement method.water displacement method.

2.2. Measure the volume, temperature, Measure the volume, temperature, and pressure of a sample of gas.and pressure of a sample of gas.

3.3. Calculate the molecular mass of a Calculate the molecular mass of a gas using the ideal gas equation.gas using the ideal gas equation.

ProcedureProcedure

In this lab, students In this lab, students collected butane gas collected butane gas from a common from a common lighter using the lighter using the water displacement water displacement method using the method using the equipment shown at equipment shown at the right. Advance to the right. Advance to the next slide and the next slide and then read through the then read through the procedure of the lab procedure of the lab to familiarize yourself to familiarize yourself with this method.with this method.

ProcedureProcedure

Beaker

Eudiometer (gas collection tube)

Thermometer

Trough

Step 1Step 1

The procedure The procedure asks you to read asks you to read the initial mass of the initial mass of the lighter. The the lighter. The measurement is measurement is shown to the shown to the right. Record the right. Record the value on your data value on your data table.table.

Step 2Step 2

In this step, you In this step, you are to set up the are to set up the eudiometer for eudiometer for gas collection. gas collection. The picture at The picture at the right shows the right shows the eudiometer the eudiometer filled completely filled completely with water.with water.

Step 3Step 3

The filling of the The filling of the eudiometer with eudiometer with butane is shown in butane is shown in the pictures below. the pictures below.

Step 4Step 4

Read the Read the volume of the volume of the butane in the butane in the eudiometer as eudiometer as shown in the shown in the picture at left picture at left and record and record this value on this value on your data your data table.table.

Step 4Step 4Read the temperature of the room off Read the temperature of the room off the thermometer shown below. The the thermometer shown below. The units on the thermometer are units on the thermometer are ooC.C.

Step 5Step 5

The final mass of The final mass of the lighter is the lighter is shown in the shown in the picture on the picture on the right. Record right. Record this on your data this on your data table.table.

Step 6Step 6The barometric pressure was obtained from the The barometric pressure was obtained from the

national weather service website which is shown national weather service website which is shown below. Record this value on your data table below. Record this value on your data table under atmospheric pressure. (The unit is inHg.) under atmospheric pressure. (The unit is inHg.)

Determining the pressure Determining the pressure of the butane gasof the butane gas

The eudiometer does not just contain The eudiometer does not just contain butane. Evaporated water is also inside butane. Evaporated water is also inside the tube and the pressure of this vapor the tube and the pressure of this vapor must be accounted for. To do this, we must be accounted for. To do this, we must use Dalton’s Law which states that must use Dalton’s Law which states that the total pressure in a container is equal the total pressure in a container is equal to the sum of the partial pressures of the to the sum of the partial pressures of the gases in the container. Mathematically, gases in the container. Mathematically,

PPTotal Total = P= P11 + P + P22 + P + P33 + … + …

(continue on next slide)(continue on next slide)

Determining the pressure Determining the pressure of the butane gasof the butane gas

So, the total pressure inside the So, the total pressure inside the eudiometer is equal to the pressure of the eudiometer is equal to the pressure of the butane plus the pressure of the water butane plus the pressure of the water vapor. The total pressure is also equal to vapor. The total pressure is also equal to the atmospheric pressure. The water the atmospheric pressure. The water vapor pressure can be obtained from the vapor pressure can be obtained from the table on your lab sheet. Then use the table on your lab sheet. Then use the following equation to solve for the following equation to solve for the pressure of the butane. Be careful with pressure of the butane. Be careful with units!units!

PPatmatm = P = Pbutanebutane + P + Pwater vaporwater vapor

Good luck!!!Good luck!!!