Determining the Mole Ratios in a Chemical Reaction PDF

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4/7/16

Determining the Mole Ratios in a Chemical Reaction Introduction: The mole ratios of reactants and products can be found from a balanced chemical reaction. Identifying the mole-to-mole ratio allows further stoichiometric calculations to be made. The mole ratio of the reagents could be found by the amount of heat released during the reaction to find out the change in temperature. The purpose of this experiment its to determine the stoichiometric ratio between NaOH and an unknown acid in a chemical reaction. Furthermore, the greatest amount of reactants will be consumed and the greatest amount of products will be formed. This identifies the ratio of moles of reactants in the reaction. We will prepare a series of mixtures of the two reactants. The mixture that generates the most heat energy will be the reaction that completely consumes both the unknown acid, and NaOH which tells is that its an exothermic reaction. Then the unidentified acid will be determined if it's a monotropic, ditropic, or tritropic acid. Monotropic acids donate one proton per molecule like HCl and acetic acid. Ditropic acids donate two protons per molecule, like sulfuric and carbonic acids, and tritropic donate three protons per molecule as in the case of phosphoric and citric acids. Procedure: Before starting the experiment between the acid and base, we collected the following materials:         

LabQuest Temperature probe Two 10 ml graduated cylinders Two 25 ml graduated cylinders Two 50 ml graduated cylinders 1.0 M sodium hydroxide, NaOH, solution 1.0 M unidentified acid solution Three 250 ml beakers Foam cups

Before starting, we all wore goggles and gloves. After connecting the temperature probe to the LabQuest, we obtained about 125 ml of NaOH and 75 ml of the unknown acid. We measured 30 ml of the NaOH

solution, poured it into a foam cup then inserted a temperature probe into the cup. (We balanced the foam cups by placing them onto beakers.) After measuring the 30 ml of the unknown 1.0 M acid solution, we gently stirred the NaOH solution with the temperature until the temperature readings became constant. A few seconds after starting data collection, we added the acid to the NaOH solution in the cup. When the data collection stopped after 3 minutes, we recorded the maximum temperature change on the graph. We then disposed of the reaction mixture and rinsed the vessels. We continued these steps by conducting the second acid to base ratio experiment with 40 ml of NaOH and 20 ml of the unknown acid. Yet again, we did the experiment one last time, this time using 45 ml of the base and 15 ml of the acid, rinsing out all the utensils after and putting away all the materials.

Conclusion: The purpose of this experiment was to measure the temperature changes of a series of reactions, determine the stoichiometry of a reaction in which one of the reactants is known but the other reactant and the products are unknown, determining whether the unidentified acid was monoprotic, diprotic or tripotic. What we observed during the experiment, was that everytime we poured the acid into the NaOH and recorded the temperature, it increased drastically. 30mL of NaOH, measured is 22.5 Celsius, after pouring in 30mL of the unknown acid it increased to 28.5 Celsius. The difference in temperature was 6.0 Celsius. After repeating this process two more times, the data

recovered showed an increase on every try. As we repeated the process, we poured in more of the NaOH and less of the unknown acid. After the second try the change of temperature was 8.8 Celsius and after the third try the change of temperature was 9.3 Celsius. We then determined that the 30mL of NaOH and 30mL of the unknown substance was monoprotic, 40mL of NaOH and 20mL of the unknown substance was diprotic, and 45mL of NaOH and 15mL was triprotic....