Title: the Molar Volume of a Gas (AKA the Cage of Death Lab )

Title: The Molar Volume of a Gas (AKA “The Cage of Death Lab”) Name:

Purpose: To 1. collect over water a volume of hydrogen gas produced by the reaction between magnesium metal and hydrochloric acid; 2. determine the partial pressure of the hydrogen gas; 3. determine the volume occupied by one mole of hydrogen at room conditions, using experimental results.

Procedure: 1. Measure the length of your magnesium ribbon to the nearest 0.5mm. 2. Measure and pour (carefully) 10 mL of concentrated HCl into a gas-collecting tube. 3. Using a squirt bottle, fill the tube slowly with distilled water, taking care not to mix liquids in the tube. Dislodge bubbles by tapping the tube. 4. Roll Mg ribbon into a cylinder. Wrap nichrome wire around the ribbon to form a cage (of death), leaving about 6 cm of wire. 5. Insert the Mg ribbon inside its cage of wire into the gas-collection tube about 5 cm from the top. Wrap the end of the wire around the outside of the gas tube to hold it in place. 6. Place your thumb over the end, making sure that no air is trapped inside the tube. 7. Invert the gas tube into a beaker of water. 8. When the bubbling stops, tap bubbles off the side of the container. 9. Equalize the level inside the tube with the water level outside the tube by inverting into a large graduated cylinder and raising or lowering the gas-collection tube until the water levels inside the tube and the graduated cylinder are the same. This means the pressure inside the tube is equal to the atmospheric pressure. 10. Read the level of the gas inside the tube (at the bottom of the meniscus). Record this volume as the volume of gas hydrogen gas collected. 11. Record room temperature and barometric (atmospheric) pressure. Also record the vapor pressure at room temperature (on a table provided to you). 12. Pour the liquid contents of both the beaker and the gas collection tube down the sink and rinse with water. Make sure to put the nichrome wire cage back up front so it can be reused. Do not leave it in the sink!

Data: Mass of 1000.mm of Mg ribbon ______Length of Mg ribbon used ______

Volume of collected hydrogen gas (after correcting to atmospheric pressure) ______

Atmospheric pressure ______Room temperature ______

Vapor pressure of water under room conditions ______

Calculations: 1. Using the mass of one meter (1000 millimeters) of Mg ribbon, calculate the mass of your small piece of ribbon using proportional reasoning.

2. Calculate the number of moles of Mg reacting in your experiment. Convert from grams to moles. 3. Write a balanced equation for the reaction in this experiment. Include symbols for state of matter.

4. Calculate the number of moles of hydrogen gas that should have been produced by your reaction assuming all the magnesium reacted. Get stoiched.

5. Since the hydrogen gas was bubbled through water, some of the gas volume that you measured is actually water vapor instead of hydrogen gas. To account for this, use Dalton’s Law to subtract the vapor pressure of water at room temperature from the barometric pressure. This is the portion of the pressure that is due to the hydrogen gas.

6. Using the number of moles of H2 collected (determined in step 4), and the volume of hydrogen gas collected, determine the experimental volume of one mole of gas under these room conditions. Use proportional reasoning.

7. Using the Combined Gas Law ( P1V1/T1 = P2V2/T2), calculate what the volume of one mole of gas would be at standard temperature and pressure (STP).

Error Analysis: The correct molar volume of a gas at STP is 22.4L. Calculate your percent error and account for your error.