Stoichiometry I: Determining the Percent Composition
of Ammonium Chloride, Salt, and Sand in a Mixture
To be assigned by your lab instructor.
Student Learning Outcomes:
By the end of this lab, the student should be able to calculate the percent composition of a mixture.
The student should understand the concept of determining the mass of a substance by taking the difference of two other masses.
Learn how to use physical properties to separate the components of a mixture.
The purpose of this procedure is to determine the percent composition of an unknown mixture that contains ammonium chloride (NH4Cl), salt (NaCl), and sand, [(SiO2)n].
This lab is the first of a series of procedures which are designed to introduce the concept of stoichiometry, the study of the numerical relationships in chemical formulas and reactions. In this procedure, we will be dealing with a mixture of three compounds: ammonium chloride, salt, and sand. These compounds will be separated and weighed by exploiting differences in their physical properties. In the next experiment (Determining the Percent Composition of Potassium Chlorate in a Mixture), we will perform a similar analysis, but instead we will exploit a difference in the chemical properties of the substances being analyzed.
Most solid substances, when heated, undergo a phase transition from the solid phase to the liquid phase, a process known as melting. However, some substances go from the solid phase directly to the gas phase, a process known as sublimation. (A familiar example is frozen carbon dioxide, or dry ice. If you put a chunk of dry ice on a tabletop, the dry ice does not melt, but the chunk gets smaller and smaller as the particles in the solid warm up and go directly into the gas phase.) Ammonium chloride sublimes when heated, which gives us a convenient way to separate ammonium chloride from salt and sand. By knowing...