Lab: Molar Volume

Post Author: Georgia A. 

Homework:

1) 2 WebAssigns are due tonight @ 11:59pm 

2) Watch the video going over the prelab problems for the lab you did today, and take notes (check in tomorrow).  The write-up for this lab is due Monday, 11/25.

3) Print out a copy of the Unit 5 Review Packet (in the Unit 5 Handouts folder) and start work on it tonight!  Our unit test is on Tuesday, 11/26.

4) If you were uncertain about the manometer calculations you did for homework last night, check your work against the key posted in the Unit 5 Keys folder

Lab

Background and Purpose:

The "molar volume" of a gas is the amount of space one mole of a gas occupies at Standard Temperature (0℃) and Standard Pressure (1.0 atm). Standard Temperature and Pressure are abbreviated "STP." As it turns out, this number is always the same: one mole of gas (ANY gas) at STP always occupies 22.4 litters. In this lab you will attempt to demonstrate this fact. 

Pre-Lab Questions:

Reaction of 0.0285 g of magnesium with excess hydrochloric acid generated 31.0 mL of hydrogen gas. The gas was collected by water displacement in a 22.0℃ water bath. The barometric pressure in the lab was 746.4 mmHg. 

1. Use Dalton's law and the vapor pressure of water at 22.0℃ to calculate the partial pressure of hydrogen gas in the tube. 

2. Use the Combined Gas Law to calculate the corrected volume of hydrogen at STP

3. What is the theoretical number of moles of hydrogen that can be produced from 0.0285 g of Mg?

4. Divide the corrected volume of hydrogen by the theoretical number of moles of hydrogen to calculate the molar volume of hydrogen at STP.

Lab Write-up

1. Title

2. Purpose 

3. Data

4. Calculations: Use data from both trials 

       a. Write and balance the reaction between magnesium and hydrochloric acid

       b. Calculate the mass of magnesium and then calculate the moles of magnesium for each of the two trials (Recall that 1.00 cm of magnesium ribbon has a mass of 0.01085 grams)

       c. Using stoichiometry, calculate the moles of H2 produced for each trial.

       d. Using Dalton's Law of Partial Pressures, calculate the pressure of the H2 gas in the eudiometer for each trial.

       e. Using the Combined Gas Law, calculate the volume of the H2 gas at STP for each trial.

       f. Calculate the molar volume of a gas at STP for each trial. Average the two molar volumes to get the final molar volume you will report in your conclusion

       g. Calculate the percent error of your reported molar volume.

       h. In setting up this experiment, a student noticed that a bubble of air leaked into the eudiometer. What effect would this have on the measured volume of a hydrogen gas? Would the calculated molar volume of hydrogen be too high or low? 

Conclusion

a. Claim - state here what you found the molar volume of the hydrogen gas to be.

b. Evidence - What data led you to this conclusion? Talk through the logical steps that led you from the data you measured in class to the claim stated above.

c. Reasoning - How close were you to the actual molar volume of a gas? What was your percent error? What SPECIFIC mistakes in the lab could have caused the error in your results? 

Data:

Observations: 

 It starts bubbling from the Magnesium and Copper at the bottom of the eudiometer. Bubbles rush faster as time progresses. The gas is pushing the H2O out of the rubber stopper. A space full of Hydrogen gas starts forming at the top. 

Next Author: Pamela H.