Analysis of an Unknown Mixture Using the Ideal Gas Law

PURPOSE OF EXPERIMENT Determine the percent composition by mass of an unknown mixture of sodium nitrite, NaN02, and sodium chloride, NaCl, after collecting a gas evolved by reaction of NaN02. 

A mixture is composed of two or more substances that do not react with each other. The possible compositions of some mixtures may vary over a wide range. Mixtures are encountered frequently both in nature and in the laboratory. Salt beds, salt brines, and sea water - major sources of many important salts - are mixtures. The desired product in most chemical syntheses is part of a mixture composed of other reaction products as well as undesired side products and left over reactants. A heterogeneous mixture like the unknown in this experiment can have an irregularly variable composition, structure, and physical and chemical behavior such that abrupt discontinuities or boundaries may be observed. Cement and topsoil are examples of heterogeneous mixtures. 

One of the methods of determining the percent composition by mass of a mixture is to measure quantitatively the amount of product formed by reaction of one of the components under conditions where the other component is inert and remains unreacted. If one of the products is a gas, that gas can be collected, its volume can be determined under measured conditions of pressure and temperature, and the number of moles of gaseous product can be calculated using a rearranged form of the Ideal Gas Law. The moles of product can be related back to the moles and mass of reactant from which the product was formed. By knowing the mass of one component which reacted, the mass of the other component can then be determined by difference from the total mass of unknown mixture used. Finally, percent composition by mass can be calculated. 

You will collect the N2 gas at atmospheric pressure and room temperature and calculate from your data the moles of N2, moles of NaN02/ mass of NaN02, mass of NaCl, and percent composition by mass of NaN02 and NaCl. 

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