AP Lab 9 Stoichiometry - Determining the Stoichiometry of...

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Determining the Stoichiometry of Chemical Reactions AP Chemistry Lab #9 Taylor Harris, Grace Ammons, Jackie Buckley October 17, 2010
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INTRODUCTION A double replacement reaction is considered to be irreversible because the formation of a precipitate provides a force that allows the reaction to go in only one direction. In a balanced double replacement equation, the number of moles and the ratios of moles of the reactants and the products are given. They are represented by coefficients that come before the formulas of the products and reactants in that chemical reaction. If the formulas of all products and reactants are known, then it is fairly simple to balance the equation and find the mole ratios but when the formulas are not known, experimental measurements must be used to determine the ratios. In this lab, the method of continuous variations is used to determine the mole ratio of two reactants. The total number of moles of reactants I kept constant for the series of measurements. Each measurement is made with a different mole ratio of reactants. The optimum ratio, which is also the stoichiometric ratio, should consume the greatest amount of reactants, form the greatest amount of product, and generate the most heat and temperature change if the reaction is exothermic. In this experiment, different amounts of ferric nitrate and sodium oxide solutions (part 1) and cupric chloride and sodium phosphate solutions (part 2) 2
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were combined in seven different mole ratios and the height of the precipitates, along noticeable appearances, were measured and recorded. The heights were plotted on a graph and two best-fit straight lines were drawn through the increasing and decreasing points. Where the two lines intersected is where the optimum ratio for the reaction was found. EXPERIMENTAL Purpose The purpose of this lab is to find the optimum mole ratio for the formation of a precipitate in a double replacement reaction and use this information to predict the chemical formula of the precipitate. Theory Numerous theories were proven and demonstrated in this particular experiment. One of these theories includes the concept of mole ratios. Generally, to find a portion (usually in moles) of a chemical from a known portion of another, we use a mole ratio. In this experiment mole ratios were already given in the Data tables. For example for every 1 mol of Fe(NO)3 there were 11 mols of NaOH. The law of conservation of mass was also shown in this experiment. This law generally states that whatever goes into a reaction must come out (mass wise). Stoichiometry and double replacement reactions were two concepts that were used in balancing the equation of the formulas of the solutions that were mixed together. Stoichiometry is a branch of chemistry that deals with the quantitative relationships that exist among the reactants and products in chemical reactions 3
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that typically form a ratio of whole numbers. A double displacement reaction is a chemical reaction between compounds in which the elements in the reactants
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This note was uploaded on 01/31/2012 for the course CHEMISTRY 101 taught by Professor Padolik during the Spring '11 term at University of Cincinnati.

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AP Lab 9 Stoichiometry - Determining the Stoichiometry of...

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