Stoichiometry and Limiting Reagents

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After concluding the experiment, I learned that the products reaction can be created in precise amounts when the masses of the products can be measured to exact standards. Further, I learned more about the molarity of aqueous solutions, and how that quantity, along with the volume of the solution, can be manipulated to find the exact number of moles in a given volume. In this case, experimenters were given aqueous solutions of NaOH and CaCl2 in known molarities and then had them react with one another to yield a precipitate of Ca(OH)2. The precipitate was filtered out of the remaining aqueous solution of stoichiometry. In our case, all four tests yielded more mass than should have occurred. Experimenters attribute this completely evaporated from the filtered precipitate, which would add excess mass. By dealing with such small quantities of reagents, any small inaccuracy in measurement creates a large difference in actual yield from theoretical yield.

Through simple molar calculations, using the coefficients in the balanced chemical equation( CaCl2(aq) + 2NaOH(aq) Ca(OH)2 + CaCl2), the limiting reagent could be determined from the volumes of reactants used. The number two to four tests turned out as expected, NaOH and CaCl2 respectively being the limiting reagents. In the second test, according to our calculations, the products should have completely reacted, leaving pure water after filtration. In the test, the addition of NaOH to the filtered solution yielded more precipitate, which should not have occurred if the filtrate was pure water. We hypothesize that either the products were not measured in exact quantities, or in the test the products did not completely react with one another, leaving some CaCl2 in solution.

In conclusion, by measuring reactants accurately, the products of a chemical reaction can be created to precise standards.
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