# Molar Volume of a Gas

Molar volume is the name given to the volume that one mole of any gas occupies at standard temperature and pressure. In chemistry, many of the materials worked with are gases. It is often easier to measure the volume of a sample of gas, rather than determine its mass. The main purpose of this lab is to determine the molar volume of hydrogen gas experimentally in order to compare it to the theoretical molar volume of ideal gases. In this experiment, a known mass of magnesium is reacted with an excess amount of hydrochloric acid to produce hydrogen gas. The amount of hydrogen gas produced is collected by the displacement of water. This volume is used to calculate the molar volume of hydrogen gas. This data can then be used to compare the experimental molar volume of hydrogen gas and that of ideal gases at STP (standard temperature and pressure), by first using the Combined Gas Law (P1V1/T1=P2V2/T2) to find the experimental molar volume at STP, followed by the Ideal Gas Law (PV=nRT) to find the molar volume of any gas at STP. The partial pressure of the hydrogen gas must be found before the combined gas law can be used. It is found using Dalton's Law of Partial Pressure (P=PH2+PH2O). Data and Results

Mass of Mg UsedVolume of Gas CollectedRoom TemperatureBarometric PressureWater Vapor Pressure 0.0145 g44.4 mL23.0 0C752 mmHg2.81 kPa

Sample Calculations

Combined Gas Law: P1V1/T1=P2V2/T2

Used to find the molar volume of hydrogen gas at STP.

Ideal Gas Law:

PV = nRT

(101.3 kPa)(V) = (1 mol)(8.314 L.kPa/mol.k)(273 K)

V = 22.4 L

Used to find the molar volume of any gas at STP

% Error: 100 x (theoretical value - experimental value)/ (theoretical value) Used to find the percent error.

Dalton's Law of Partial Pressure: P=PH2+PH2O

Used to find the partial pressure of the hydrogen gas.

Mg UsedH2 ProducedMolar volume of H2Pressure of H2Molar volume of H2 at STP% error 0.0017 mol0.0017 mol26.12 L.mol-197.40 kPa...

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