Experiment #8: Limiting Reactant
In chemical reactions, the significance of knowing the limiting reactant is high. In order to increase the percent yield of product, increasing the limiting reactant, possibly, is the most effective. In this experiment we were able to calculate limiting reactants from the reaction of CaCl2. 2H2O + K2C2O4.H2O(aq). As a group, we obtained our salt mixture of calcium chloride and potassium oxalate, and weighed the mixture. We were able to make an aqueous solution from the mixture and distilled water. We boiled and filtered off the solution, leaving the precipitate. Once the precipitate was dried overnight, it was weighed and the mass was measured. Then we calculated the moles of the precipitate. From these calculations, we established moles of the limiting reactant, were the same amount of moles in the product based on the stoichiometrically balanced equation. Next the percent yield of the limiting reactant was calculated. In Part B of this experiment, two solutions were added to the aqueous product in order to determine the limiting reactant. Once each solution was added, we were able to visibly see the precipitate forming when 0.5 M CaCl2 was added. This made us conclude the limiting reactant was in fact CaCl2. Introduction
Stoichiometry is a section of chemistry that involves using relationships between reactants and/or products in a chemical reaction to determine desired quantitative data. Doing stoichiometry can calculate masses, moles, and percent’s with a chemical equation. The use of stoichiometry is how we were able to find the limiting reagent in this lab. We know that the limiting reagent is the chemical that will be used up first. Two factors affect the yield of product in a chemical reaction: the amounts of starting materials and the percent yield of the reaction. Under certain conditions such as temperature and pressure, can be adjusted to increase the yield of a desired product in a chemical reaction but because the chemicals react according to fixed mole ratios, only a limited amount of product can form from measured amounts of starting materials. A way for us to better understand this concept of the limiting reactant is to observe the reaction in our experiment. The reaction of calcium chloride dehydrate, CaCl2·2H2O, and potassium oxalate monohydrate, K2C2O4·H2O, in an aqueous solution. For the reaction system in this experiment, both the calcium chloride and potassium oxalate are soluble salts, but the calcium oxalate is insoluble. The ionic equation for the reaction is Ca2+(aq)+2Cl-(aq)+2K+(aq)+C2O42-(aq)+3H2O(l)®CaC2O4·H2O(s)+2Cl-(aq)+2K+(aq)+2H2O(l) presenting only the ions that show evidence of a chemical reaction, formation of a precipitate, and by removing the spectator ions, no change of ionic form during the reaction, we have the net ionic equation for the observed reaction: is Ca2+(aq)+ C2O42-(aq)+H2O(l)®CaC2O4·H2O(s). In Part A of this experiment the solid reactant salts CaCl2·H2O forms and K2C2O4·H2O form heterogeneous mixture of unknown composition. The mass of the solid mixture is measured and then added to water-insoluble CaC2O4·H2O forms. The CaC2O4·H2O precipitate is collected by gravity filtration and dried, and its mass is measured. In Part B, the limiting reactant for the formation of solid calcium oxalate monohydrate is determined from two precipitation test of the final reactant mixture from Part A. The first test we tested the mixture for an excess of calcium ion with an oxalate reagent and the second test the mixture is tested again for an excess of oxalate ion with calcium reagents. Materials and Methods
1 250ml beaker
1 piece of filter paper
1-2 grams of salt mixture
A hot plate
A weighing scale
1. Experimenters obtained one 250 ml beaker and weighed it on the weighing scale and recorded the results 2. The 250 ml beaker was then filled with 1-2 grams of the salt...
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UC Davis ChemWiki. Stoichiometry and Balancing Reactions. http://chemwiki.ucdavis.edu/Analytical_Chemistry/Chemical_Reactions/Stoichiometry_and_Balancing_Reactions
UCCS Chem 103 Laboratory Manual. Experiment 3 Limiting Reactants. http://www.uccs.edu/Documents/chemistry/nsf/103%20Expt3V-LR.pdf
Masterson, W, Hurley, C. Chemistry: Principles and Reactions. 6th ed. Belmont, CA: Brooks/Cole Cengage Learning; 2009.
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