LAB #3.2: MOLAR VOLUME OF HYDROGEN

## Background Information

The term, molar volume, refers to the volume of one mole. Since volume varies with temperature and pressure, it would be meaningless to compare volumes measured under different conditions. It is therefore customary to make the measurements under convenient laboratory conditions and then convert the measurements to the volume at standard temperature and pressure (STP, 0°C and 1 atm).

For an ideal gas, the size of a gas sample is insignificant compared to the size of the container holding the gas, and there is no interparticle interaction (no attraction nor repulsion between particles). The molar volume of the gas at a particular temperature and pressure is independent of the type of gas.

In this experiment, hydrogen gas generated by the reaction of magnesium with hydrochloric acid is collected over water.

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

The volume of the gas is measured and the number of moles of gas is calculated from the mass of the magnesium strip used. By dividing the volume by the number of moles we obtain the molar volume at the temperature and pressure at which the experiment is performed. In order to find the molar volume at STP, we apply the Ideal Gas Law:

P V = n R T

where P = the pressure of the gas

V = the volume of the gas

n = the number of moles of gas

R = gas constant

T = the temperature in K

## Experimental Set-up

The following video provides the concept of the lab that you are going to do. Please make sure that you follow our written procedure provided to you, which is also posted below. Please take note of the following that we will NOT do which was described/demonstrated in the video:

• try NOT to poke around with a glass stirring rod.

## Lab Handouts, Analysis & Calculations

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Preview: The following are the sections contained in the document below:

1. Lab Procedure Handout

2. Pre-Study Worksheet with Answer Key

3. Sample data

4. Sample calculations

5. Possible sources of error

6. Links to Similar labs/ Resources 08 - Molar Volume of Hydrogen [HAC]