Experimental determination of the molar volume of a gas at STP
Name: ________________________
Period: __________________
Lab Station: ____________________
Partners: _________________
I.
II.
III.
Purpose: The purpose of this lab is to experimentally determine the volume a
mole of hydrogen will occupy at STP.
Materials:
1cm piece of magnesium, 400mL and 250mL beakers, gas collection tube, 1.5 –
2.0mL of concentrated HCl, metal rod, buret clamp, thermometer, and of course,
goggles
Procedure:
You MUST wear safety goggles at ALL TIMES! Hydrochloric Acid
burns!
1. Obtain a small(about 2-cm) piece of magnesium ribbon and measure its mass.
Record.
2. Prepare a piece of copper wire to serve as a cage for your strip of magnesium. Wrap
a small piece of wire around your finger a few times to make the basic cage.
3. Prepare the set-up shown in Figure 1. Half fill a 400mL beaker with tap water.
4. Add about 1.5 to 2mL of concentrated HCl to the tube. You can measure the volume
added by on the tube.
5. Use the water in the 250mL beaker to SLOWLY fill the gas collection tube with
water.
6. Slide the copper wire along into the tube such that the piece of magnesium will be in
the gas collection tube and tape the copper to the tube. Cover the end of the tube
with a small piece of paraffin or your finger and invert the tube under the water in the
400mL beaker.
7. Secure the gas collection tube with the clamp attached to the metal rod in your table.
8. After all of the bubbles have stopped and all of the magnesium reacted, measure the
final volume in the tube and record.
9. Record the barometric pressure and water temperature on your data chart. Dump
the water down the drain and CLEAN UP YOUR LAB AREA!
Data Chart:
1. Length of Magnesium: _________ cm
2. Mass of Magnesium: _________ grams
3. Barometer Reading: _________ mm Hg
4. Volume of Hydrogen: _________ mL
5.
= _________ L
6. Water Temperature: _________ 0C
7.
= _________ K
8. Height of water in tube: ________ mm
Molar Volume of a Gas at STP Lab
Name:
Show all of your work to receive credit for each question.
Score:
IV.
Calculations:
1. Moles of magnesium
________ mol
2. Correction factor to convert water
________ mm Hg
height to mercury (barometric) height
[Height of water in tube/13.6]
3. Vapor pressure of water at the
________ mm Hg
specified temperature (Look it up).
4. Pressure of Hydrogen in tube
________ mm Hg
(barometer – vapor pressure of water –
correction factor)
5. Pressure of Hydrogen in kPa
________ kPa
(measurement in mm Hg x 101 kPa/760
mm Hg)
6. Moles of hydrogen, actual (PV = nRT),
________ mol
R = 8.31 kPa*L/mol*K
7. Moles of hydrogen, theoretical
________ mol
8. % Error [|(#7-#6)/#7|x100]
________ %
9. Write the balanced chemical equation
for the reaction.
10. How would your results have been
different if you would have produced
oxygen instead of hydrogen?
Calculations/Questions(show ALL work)
11. Write the balanced equation for the reaction. What type of reaction is this?
12. Calculate the number of moles of magnesium that reacted.
13. Calculate the number of moles of hydrogen produced based on the mole ratio
between magnesium and hydrogen.
14. Calculate the experimental value for the volume of a mole of hydrogen. Use the
experimental volume(in Liters) divided by the experimental number of moles of
hydrogen.
15. What is the volume of a mole of any gas at STP?
16. Calculate what volume a mole of a gas would take up in class the day of the lab.
Use the combined gas law(P1V1/T1 = P2V2/T2). The result of this calculation is your
expected value.
17. Calculate your percent error by using the equation:
Percent error = (experimental – expected)/expected x 100
18. How would your results have been different if you would have produced oxygen gas
instead of hydrogen?