Stoichiometry Lab Manual - Introduction to Chemistry Lab | CHEM 1045, Lab Reports of Chemistry

Download Stoichiometry Lab Manual - Introduction to Chemistry Lab | CHEM 1045 and more Lab Reports Chemistry in PDF only on Docsity! Date Performed: 10/12/09 Name: Date Submitted: 10/19/09 Partner: Instructor: Stoichometry Objective  To determine the stoichometry of the reaction between potassium iodide (KI) and sodium hypochlorite (NaClO) in an aqueous solution. Experimental Data Vol. NaClO (mL) Vol. KI (mL) TI NaClO (°C) TI KI (°C) TF (°C) 45.0 5.00 21.48 20.64 24.26 40.0 10.0 21.93 21.51 27.95 35.0 15.0 21.75 21.30 27.08 30.0 20.0 21.72 21.25 27.09 25.0 25.0 21.55 21.96 26.25 20.0 30.0 22.40 21.50 25.30 15.0 35.0 21.95 21.25 23.99 10.0 40.0 21.91 21.23 23.03 5.00 45.0 22.11 21.30 22.14 Sample Calculations 1) Mole Fraction NaClO Vol−NaClO Vol−Total = 40 .0mL 40 .0mL+10 .0mL = 0.80 mole NaClO 1-0.80 mole NaClO= 0.20 mole KI a/b=mole frac NaClO/mole frac KI= 0.80/0.20= a/b= 4 moles NaClO/1 mole KI 2) Weighted Temperature TInitial= (T1V 1 )+(T 2V 2 ) (V 1+V 2 ) = (21.48 ´ 45.0 )+(20 .64 ´ 5.00 ) (45 .0+5 .00 ) = 21.4°C 3) TΔT TInitial - TFinal = 24.26°C -21.4°C = 2.86 °C Results and Conclusions Vol. NaClO (mL) Vol. KI (mL) TI NaClO (°C) TI KI (°C) TI (°C) TF (°C) Δt (°C)t (°C) Mole fraction NaClO Mole fractio n KI 45.0 5.00 21.48 20.64 21.40 24.26 2.86 0.90 0.10 40.0 10.0 21.93 21.51 21.84 27.95 6.15 0.80 0.20 35.0 15.0 21.75 21.30 21.60 27.08 5.48 0.70 0.30 30.0 20.0 21.72 21.25 21.51 27.09 5.59 0.60 0.40 25.0 25.0 21.55 21.96 21.84 26.25 4.45 0.50 0.50 20.0 30.0 22.40 21.50 21.90 25.30 3.40 0.40 0.60 15.0 35.0 21.95 21.25 21.54 23.99 2.49 0.30 0.70 10.0 40.0 21.91 21.23 21.42 23.03 1.63 0.20 0.80 5.00 45.0 22.11 21.30 21.30 22.14 0.84 0.10 0.90 The maximum heat released during the reaction determined the stochiometric coefficients (a and b), and is visible on the following graph. By drawing a line down from where the lines of best fit intersected on the graph of T vs Mole fraction of ΔT NaClO, it is obvious that the maximum heat was released during the reaction when the mole fraction of NaClO was about 0.75. This is also clear in the large jump in T ΔT when the mole fraction is 0.80. A more exact value can be found by setting both equations of the lines equal to one another and solving for x. (8.6604x=-26.214x +26) This results in an x value of .7455. I determined the mole ratio to be 0.75/0.25 by subtracting the mole fraction of NaClO from 1, which gave me the mole fraction of KI (1-0.75=0.25). The coefficient ratio (a/b) is then 3/1. Discussion of Experiemtnal Uncertainty I was not given the accepted value for mole ratio in this lab so I am unable to say whether or not my result is close to the true value. There were a few instances throughout the lab where error was possible. When diluting the blach and KI solution, small errors in measurement could have thrown off the data. I also noticed that if the temperature probe was not thoroughly clean after each reading, the residue from the solution caused a higher initial temperature. This occurred as a result of a small exothermic reaction between the solution and the residue left on the probe. Answers to Questions a. Stochiometric Coefficient- a numerical expression in a balanced chemical equation that represents the proportions between the numbers of moles of reactants used and the products formed. b. Mole Fraction- a way to express the composition of a mixture. c. Moles of Substance/Moles of Substance + Moles of other substances in mixture