Tutorial #6.5 Effusion Experiment 2 Draft 8.13.01

Part 1.

Questions: How is the molecular weight or a gas related to the time it takes for it to escape from a pinhole in a container? How is the molecular weight of a gas related to its rate of escape?

This tutorial accompanies the effusion experiment #2 simulation.

In this experiment, a syringe is filled with a gas. The syringe has markings on it to indicate the volume (in mL) of the gas in the syringe. You can choose the gases you wish to investigate from the menu of available gases. In this experiment, the initial temperature of each gas is 25.0°C or 298K. [You can measure the pressure of the gas. You can measure the mass of the gas.] The syringe needle is plunged into an evacuated flask (a flask with no air or other gas in it - a vacuum) and the gas starts to escape from the end of the needle into the evacuated flask. You can time how long it takes for the piston to move from the starting point (250.0 mL ) to a point lower on the syringe 0.0 mL ).

If different gases are placed into the syringe, at the same temperature and pressure and then allowed to escape (leak out) through a pinhole located at the end of the needle. You can compare the rates of escape, in units of mL/sec, for each gas tested. You will first be working with known gases

 Experimental set-up and more questions. Data Collection. Web simulation #40.

For this first set of experiments, we suggest that you keep the initial temperature of each gas at 298K and the initial pressure of each gas at 1.00 atm.

Here are several questions for you and your group to investigate:

You will need to design your experiment. In your experiment, what is the dependent variable? What are the independent variables? You will need to construct a data table.

Of the gases available to investigate: Which gas escapes from the syringe fastest? Which gas escapes from the syringe slowest? Explain what you mean by fastest.

The time it takes for a gas to escape can be measured by using a timer. However, another measure of how fast or slow a gas escapes is the rate. How will you determine the rate of escape of a gas?

In order to answer the two main questions, you will need to find a linear relationship between two variables. One of the variables will be rate (and or time). What is the other variable?

How is the molecular weight of a gas related to the time it takes for it to escape? Plot a graph.

How is the rate of escape of a gas related to its molecular weight? Plot a graph.

Other questions: How is the density of a gas related to the time it takes for it to escape? Plot a graph.

Addtional Data for Experiment #40 The Great Escape

Gas	MW	Time (sec)	Rate (mL/sec)
hydrogen	2.0000
helium	4.0000	9.89
methane	16.000	19.80
oxygen	32.000
sulfur dioxide	64.000	39.60
hydrogen iodide	128.00
unknown gas

Check your work with a staff member.

Once you have successfully identified the linear relationships, you should be able to write an equation that summarizes the main realtionship.

You can use this information in Part 2.

Define the term effusion..

Part 2. Determine the molecular weight of an unknown gas.

The Effusion Experiment #2 has the information you need to determine the molecular weight of an unknown gas.

Part 3. A model for effusion.

Which gas effuses faster through a hole of a given size, oxygen or xenon? Draw a picture diagram at the particulate nature of matter of this experiment. Show a small volume of each gas (1.00 x 10-21 L) initially. Show, relatively, how many molecules of each gas effuse after a very short period of time.

Situation 1. Assume each gas follows ideal gas behavior. Assume each gas is at the same initial temperature, volume and pressure.

Situation 2. Assume each gas is a real gas. Assume each gas is at the same initial temperature and volume. Explain, using the kinetic molecular theory, why one gas has a higher rate of effusion than the other.

Part 4. Applying the model.

Compare the rate of effusion of two gases, hydrogen and oxygen.

The rate of effusion of hydrogen gas is __________________ as the rate of effusion of oxygen gas.

Write an algebraic expression for this statement.

Compare the time it takes for equal volumes of hydrogen gas nd oxygen gas at the the same temperature and pressure to effuse through the same pinhole. of two gases, hydrogen and oxygen.

The time it takes for the effusion of hydrogen gas is __________________ as the time it takes for of effusion of oxygen gas.

Write an algebraic expression for this statement.

When you discuss effusion in terms of rate and time, what is the difference.