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Molar Mass of Metals

Here is a nice lab idea by James Gordon, Amber Boyce, and Thoren Maule (Central Methodist University, Fayette, MO) that was published in The Chemical Educator (2004, 9, 1-2). Their experiment uses our Gas Pressure Sensor to collect data using the DataMate program and a TI calculator, but it can be easily adapted for Logger Pro, EasyData, or Data Pro software.

Pressure vs Time graph of hydrogen gas generated by reaction

In the described experiment, small samples of manganese (0.0500 g) and zinc (0.0600 g) were reacted with 10 mL of 6.0 M HCl in a 250 mL Erlenmeyer flask, according to the general equation:

M(s) + 2 HCl(aq) MCl2(aq) + H2(g)

The pressure of the hydrogen gas generated was measured with the Gas Pressure Sensor, as shown here. (Note that the pressure “bump” at the beginning is due to the stopper being added, and is used as the baseline pressure value.) The change in pressure, the temperature, and the volume of the system were used to calculate moles of hydrogen gas, using the ideal gas law:

Ideal Gas Law Equation

Using the mass and moles of the metals, the average molar masses of manganese and zinc were determined to be 54.3 ± 2.5 g/mol and 62.4 ± 2.9 g/mol, respectively.

We recommend reading the original article on line at http://chemeducator.org/bibs/0009006/960364jg.htm for important tips and details.

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