Determination of the Molar Volume of a Gas and the Universal Gas Constant

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EXPERIMENT NO. 6
DETERMINATION OF THE MOLAR VOLUME OF A GAS
AND THE UNIVERSAL GAS CONSTANT

Salve, Ryan AngeloTAB3, Group 6, Mr. John Kevin Paulo Biadomang
Tabor, Frances HermilynMarch 8, 2013
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I. Abstract

This experiment is working with the ideal gas law, which is the summation of Boyle’s Law, where pressure is inversely proportional to volume, Charles’ Law, where the volume is directly proportional to temperature and Avogadro’s Law, where the volume is directly proportional to moles. In this experiment, the volume occupied by one mole of H2 was determined. By measuring the volume of H2 gas generated, its molar volume can also be calculated. The universal gas constant can be determined using the ideal gas law.

The experiment was done by inverting a graduated cylinder containing HCl and water with the cork assembly that was placed in its mouth into a beaker of ¾ full. The cork assembly was done by using a paper clip with a small piece of Mg ribbon attached to it. Using the equations of gas law, the universal gas constant and the molar volume were calculated. The experiment results lead us into a conclusion that there are possible errors happened during the experiment that made it different from the desired result.

II. Keywords: gases, molar volume, gas laws, vapour pressure, partial pressure -------------------------------------------------

III. Introduction
A gas is the state of matter that is characterized by having neither a fixed shape nor a fixed volume. Gases exert pressure, are compressible, have low densities and diffuse rapidly when mixed with other gases. On a molecular level, gases are best described as independent molecules separated by large distances in constant random motion.

Four measurable properties can be used to describe a gas: pressure (P), volume (V), temperature (T) and mole quantity (n). The relationships among these properties are summarized by the Gas Laws.

Table 1. Gas Laws
Boyle’s Law| Charles’ Law| Avogadro’s Law|
P1V1 = P2V2| V1/T1 = V2/T2| V1/n1 = V2/n2|

When Boyle’s Law and Charles’s Law are combined together the Combined Gas Law is obtained:

P1V1/T1 = P2V2/T2

When all three Gas Laws are combined together, the Ideal Gas Law is obtained:

PV = nRT

The “R” in the Ideal Gas Law is a proportionality constant called the gas constant, and has an accepted value of 0.08206 L•atm/K•mol.

A closer look at the Ideal Gas Law reveals that different gases will have identical volumes as long as they contain the same number of moles, and have the same P and T. For example, under conditions of standard temperature and pressure (273 K and 1 atm) or STP, a 1-mole sample of any gas occupies a volume of 22.4 L. This is known as the molar volume of a gas at STP.

The purpose of this is experiment is to determine the value of the universal gas constant, R, and the molar volume, Vm, of a gas by reacting magnesium with hydrochloric acid. After the experimental value has been calculated, the percent error of the calculated value of R and the molar volume of hydrogen will be determined from the universal gas constant and the accepted value of molar volume of hydrogen at STP. IV. Methodology

A 400-mL beaker was filled with water at about ¾ its capacity. A 20 cm Mg ribbon was cut into small pieces that are not longer than 0.4 cm. It was weighed and its length was recorded. One end of a paper clip was unbent and was pierced through the narrower end of the cork stopper. The Mg ribbon was inserted in the bent portion of the clip and was placed 2-3 cm from the cork. Three mL of 3M HCl was poured into a 10-mL graduated cylinder. Water was added until the graduated cylinder is full by using a wash bottle with its mouth directed to the side of the cylinder. The cork assembly was then inserted to the cylinder ensuring that the water should’ve escaped. The graduated cylinder was inverted and was put inside the...
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