Molar Volume of a Gas Determined via a Reaction between Magnesium and Hydrochloric Acid

During this experiment students will:
o gain experience using an electronic gas pressure sensor
o calculate molar volume of a gas at STP in a hands-on manner
o use the ideal gas law and combined gas law to solve a problem
Key concepts:
o Ideal gas law
o Stoichiometry
o Combined gas law
o Standard temperature and pressure (STP)
o Molar volume of a gas
Key vocabulary:
o Ideal gas, stoichiometry, STP

This lab is intended for a high school chemistry class, geared more towards and honors or AP class. This experiment will require about 2 hours worth of instructional time (30 minutes pre-lab, 1 hour for data collection, and 30 minutes for data analysis, with further data analysis that can be done outside of class). This experiment requires a gas pressure sensor and is written specifically for use with Vernier brand equipment. Students should understand how to do a stoichiometry calculation before doing this experiment. Students should have working knowledge of the ideal gas law and combined gas law before doing this experiment also. This experiment would likely be the last experiment during my gas unit. This activity could be adapted for lower level or upper level classes by changing the amount of calculation hints along the way.

This experiment would be done near the end of a gas unit as a way to illustrate how the ideal gas law, combined gas law, and molar volume of a gas all come together. Students will react ~0.01 g of Mg with 5mL of HCl solution (excess). The reaction forms hydrogen gas. Students will perform the reaction in a 125mL Erlenmeyer flask with a 2-hole stopper. Hooked up to the stopper will be a syringe (used to deliver the HCl) and a plastic tube connected to a gas pressure sensor. The gas pressure sensor will be hooked up to a Vernier interface and/or a PC depending on your equipment. Students will do 2 more trials with slightly different amounts of Mg and HCl, being sure that the HCl is in excess. By varying the amounts students will see that the molar volume of a gas does not depend on how much gas is produced and that it is in fact a constant! Students will collect their data in a form provided to them by the teacher and work through a series of calculations leading up to finding the molar volume of a gas. The calculations involve using stoichiometry to determine the amount of hydrogen gas formed, and the ideal gas law and combined gas law to determine the molar volume of a gas. Lab Handout Vernier Molar Volume Lab (Microsoft Word 145kB Aug5 08)

This lab will be difficult to finish in traditional 50-60 minute periods. Best if pre-labbed the day before.

This lab can be assessed as is - checking the students' results or it could be assigned with a formal lab report where the students are asked to further explain their findings.

Physical Science 9-12
Sub Strand: B. Chemical Reactions
Standard: The student will describe chemical reactions and the factors that influence them.
Benchmarks: 1. The student will describe chemical reactions using words and symbolic equations.
4. The student will explain how the rearrangement of atoms and molecules in a chemical reaction illustrates conservation of mass.