Stoichiometry February 28th, 2013 Abstract: The reactions of the Sodium Hydroxide and two acids, Hydrochloric Acid and Sulfuric Acid were performed. The heat given off by these two reactions was used to determine the stoichiometric ratio and the limiting reactants in each experiment. Introduction: Coefficients in a balanced equations show how many moles of each reactant is needed to react with each other and how many moles of each product that will be formed. Stoichiometry allows us to calculate the amount of reactants needed and also the amount of product.
The major basis of stoichiometry is formed by the law of definite proportions, which states that a chemical compound always contains the exact proportion of elements by mass. This is also the heart of balancing chemical equations. The coefficients of a balanced equation can also be thought of as the ratios in which the reactants combine. In the chemical equation A+ B> AB the coefficients tell us that for every one mole of reactant “A” one moles of reactant “B” are needed and used to produce the product “AB”.
If two moles of “A” was present and only one mole of “B” the excess mole of “A” would have nothing to react with. In this reaction “B” would be the limiting reactant. The reaction is limited due to “B” because once “B” is all used up, the reaction will stop, and there would be an excess of unused “A”. The progress of a reaction can be measured by the heat energy that is given off. Exothermic reactions give off heat and therefore an increase in temperature also occurs. The reaction between an acid and a base is also known as neutralization, and is usually an exothermic reaction.
When reactants are combined at stoichiometric ratios the reaction is able to be completed and would exert the most heat energy. The purpose of this lab was to carry out the reaction between a basic solution of Sodium Hydroxide with Hydrochloric acid, and also the reaction of Sodium Hydroxide with Sulfuric Acid to determine the limiting reactant and the stoichiometric ratio of each experiment. Procedure: Reaction Between HCL and NaOH Diluted Solutions of HCL and NaOH were prepared. 120 ml of 3M stock of HCl and NaOH were measured with a graduated cylinder and placed into two 250 ml beakers.
Two 400ml beakers were filled with 240 ml of water measured by graduated cylinder. The 120ml of HCl was added to one of the beakers containing water and the 120 NaOH to the other, both being added slowly while stirring the solution vigourously. Label the beakers HCl and NaOH. Keep the beakers covered with a watch glass when not in use. Measure and record the temperature of the NaOH solution using the PASCO Explorer temperature probe. Make sure to rinse off and dry the probe after every use. Obtain a coffee cup calorimeter and lid to house the reactions.
Measure the appropriate amount HCl (see chart A) pour it in the calorimeter and determine its temperature using the temperature probe. Record the temperature. Measure the corresponding amount of NaOH (see chart A) and add it to the calorimeter all at once. Put the lid back on the calorimeter and stir it carefully with the probe. Record the highest temperature reached as the reaction occurs. Rinse the cup with deionized water and dry. Repeat experiment for each of the amounts of chart A. chart A) Amount of each reactant l 1. 0 M Acid| 55. 0| 50. 0| 45. 0| 40. 0| 35. 0| 30. 0| 25. 0| 20. 0| 15. 0| 10. 0| 5. 0| ml 1. 0 M NaOH| 5. 0| 10. 0| 15. 0| 20. 0| 25. 0| 30. 0| 35. 0| 40. 0| 45. 0| 50. 0| 55. 0| *Use 100 ml graduated cylinder for measuring volumes 30 to 55 ml, 25 ml graduated cylinder for volumes 15ml through 25 ml, and 10 ml graduated cylinder for volumes 5ml and 10 ml Reaction Between H? SO? and NaOH Use the procedure from the Reaction Between HCL and NaOH only substitute the HCl with H? SO? , and the same amounts listed in chart A.
