Lab: Molar Volume of a Gas

The Goal of the Experiment

In this experiment you will collect hydrogen gas generated by a reaction between magnesium metal and hydrochloric acid. By measuring its volume and temperature, and obtaining its pressure from the current National Weather Service (NWS) report you will calculate the volume of the equivalent of one mole of gas. By using the ideal gas law, you will calculate the volume of the gas under standard conditions (Standard Temperature and Pressure, or STP), which are 0°C and 1 atm.

Follow the instructions of your teacher and use the procedure in the lab handout to carry out the experiment. Be sure to write down all of the necessary information yourself for your independently written lab report.


The Formal Lab Report

Each individual student will write and submit an independently written formal lab report.

Introduction

  1. The chemical reaction you used including a balanced chemical equation.
  2. The relevance of the proportion between the moles of a gas and volume.
  3. The method, briefly, by which you determined the volume of hydrogen gas in the experiment.
  4. The definition of the molar volume of a gas.
  5. The purpose of the lab, to calculate the molar volume of a gas at STP.

Procedure

While giving a brief overview of the steps taken to complete the experiment, be sure to include the following:

  1. How did you measure the empty space in the buret that was not marked?
  2. How did you measure the pressure of the hydrogen gas alone, not including the water vapor?
  3. Include the NWS reading for the barometric pressure.
  4. You put your buret with its contents of water and hydrogen gas into a tall cylinder of water and read the volume of gas only after equalizing the water level inside and out. Comment on why this was helpful in determining the total gas pressure inside the tube.

Data and Graphs

  1. Include a table showing Length of Mg Ribbon, Mass of Mg, Volume of H2 Gas, Volume of H2 Gas corrected to STP, Molar Volume of a Gas (L/mol). The last column requires you to calculate the number of moles of H2 and divide the STP volume by that number. Include an average value of the molar volume of a gas at STP.

Sample Calculations

  1. Show your calculation steps for one trial to find the molar volume of a gas, including the stoichiometry to find the moles of H2.
  2. Calculate a percent difference between your measured molar volume of a gas at STP and the standard value, which is 22.41 L/mol.

Analysis

  1. Report your result for the molar volume of a gas at STP.
  2. Compare your result to the standard value of 22.41 L/mol using the percent difference calculation.
  3. For each of the following comment on both how the event would have affected your final measurement of the molar volume of a gas at STP and whether or not you observed that it may have had an impact on your results. In particular, remark on whether the event would have made your result larger or smaller than the true value.
    1. How would the accidental inclusion of a bubble of air along with your hydrogen gas have affected your final measurement?
    2. How would a leak in the valve of the buret have affected your final measurement?
    3. How would a corroded piece of magnesium metal have affected your final measurement? Corroded metal is metal that has reacted with oxygen or other substances in the air to make compounds which do not react with acid in the same way the metal does.

Conclusion

Comment on the educational experience of carrying out this experiment.



Last updated: Mar 08, 2023       Home