unknown metal from Molar Mass

unknown metal from Molar Mass - Identifying an Unknown...

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Identifying an Unknown Metal from a Determination of its Molar Mass Gina Zanarini Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 Submitted on November 27, 2007 The identity of a sample metal was identified by applying gas stoichiometry, the ideal gas law, and Dalton’s law of partial pressures. Introduction The reactivity of metals varies greatly; some metals react with water, others with hydrochloric acid, and still others with oxidizing acids. In this experiment, hydrochloric acid is used to create a reaction. The hydrogen gas will bubble up through the solution and be collected over water, thus saturating it with water vapor. Using Dalton’s law of partial pressures (4), the pressure of the hydrogen gas is easily determined. If the pressure is kept constant, the increase in volume of the has will equal the volume that the wet gas would have, theoretically. The ideal gas equation can then be used to determine the number of moles of hydrogen gas. If the original sample is magnesium or zinc, the molar mass can be found with the moles of gas and mass of the sample. If the molar mass doesn’t match either of those metals, the sample would be aluminum. One would have to multiple the number of moles of gas by two-thirds to get the correct molar mass of aluminum.
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