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Kinetics

Kinetics. General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington. Purpose. To determine the rate law and the value of the reaction rate constant for a chemical reaction using the method of initial rates . Safety Considerations.

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Kinetics

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  1. Kinetics General Chemistry 101/102Laboratory ManualUniversity of North Carolina at Wilmington

  2. Purpose • To determine the rate law and the value of the reaction rate constant for a chemical reaction using the method of initial rates. • Safety Considerations • Wash your hands thoroughly after handling chemical reagents and before leaving the lab. • All chemical wastes should be placed in the labeled jar in the hood. Kinetics

  3. The general rate law for this reaction can be written as: - D [BrO3-] Rate = = k [I-]x [BrO3-]y [H+]z Dt Kinetics • Background • The chemical reaction being studied in this experiment is: 6 I- + BrO3- + 6 H+ 3 I2 + Br - + 3 H2O bromate ion • By measuring the rate of the reaction as we vary the concentrations of I-, BrO3-, and H+, we can determine the values of x, y, and z.

  4. To do this, we will add S2O32- and starch to the reaction mixture. S2O32- reacts very rapidly with I2 as shown below: thiosulfate ion tetrathionate ion I2 + 2 S2O32- 2 I- + S4O62- • When all of the S2O32- is used up, any I2that remains will react with the starch to produce a deep-blue colored complex. Kinetics • Background • Since BrO3- is colorless, we need some way to determine when a certain amount of BrO3- has reacted.

  5. By measuring the time it takes for the blue color to appear in each trial, we can determine the rate of the reaction for each trial. - D [BrO3-] Dt 3.3 x 10-5 M Rate = = Dt Kinetics • Background • The concentration of S2O32- in each trial is 2.0x10-4 M. Since there are 6 moles of S2O32- reacted for every 1 mole of BrO3- reacted, then the concentration of BrO3- reacted in each trial is 3.3x10-5 M.

  6. Kinetics • Procedure • Each trial is performed in the same manner. Use a 10 mL graduated cylinder to measure the quantities shown in Table 1 for Trial 1 into flasks labeled “A” and “B”.

  7. B • Quickly pour the contents of flask “B” into flask “A” and start the stopwatch. Record the time it takes for the solution to turn blue. Record the temperature of the blue solution. B A Kinetics • Procedure • Add 4 drops of starch solution to the flask labeled “B”.

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