After this the absorbance values of the solution were recorded every 30 seconds

After this the absorbance values of the solution were

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the reaction to start and progress. After this the absorbance values of the solution were recorded every 30 seconds. Finally, data was observed graphically using MS Excel. The absorption values vs. time were graphed in 3 ways (absorption value vs. time, ln(absorption value) vs. time, and 1/(absorption value) vs. time) to determine the order with respect to crystal violet. RAW DATA Time (min) Absorbance (A 565 ) 0:00 0.135 3:00 0.049 3:30 0.035 4:00 0.022 4:30 0.013 5:00 0.009 5:30 0.001 (See Appendix for the three graphs of absorption vs. time) CALCULATIONS/RESULTS Rate constant (k) = -slope of linear regression line = 0.0263 mol/L*s Half-life = Graphically: 1 st half-life = 2:45 min, 2 nd half-life = 45 s Calculation: 1 st half-life = [A] o /2k = .135 M/2(0.0263 mol/L*s) = 2.57 = 2:34 min 2 nd half-life = [A] o /2k = .0675 M/2(0.0263 mol/L*s) = .54 = 32 s SUMMARY/DISCUSSION The reaction order in respect to the concentration of crystal violet was zero, as evident by the linear relationship in the zero order graph. Rate law is written k[A] order [B] order , so the rate law for this reaction, in terms of crystal violet since sodium hydroxide concentration did not change appreciably, is rate = 0.0263 mol/L*s . The 1 st half-life obtained graphically varied by 7% from the 1 st half-life obtained by calculation, while the 2 nd half-life obtained graphically varied by 38% from the 2 nd half-life obtained by calculation. This variation is due to the graph size and the large increments between absorbance values which made it difficult to estimate what the time is at the right absorbance value. One improvement on this experiment would be to record absorbance values earlier than 3 minutes and more often than 30 seconds, since the reaction happened so quickly and only a few absorbance values were able to be recorded before the absorbance reached zero.
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Appendix Time (min) Absorbance ( Absorbance 0 0.135 3 0.049 3.5 0.035 4 0.022 4.5 0.013 5 0.009 Time (min) ln(Absorban Absorbance 0 -2.002480501 3 -3.015934981 3.5 -3.352407217 4 -3.816712826 4.5 -4.342805922
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5 -4.710530702 Time (min) 1/(Absorban Absorbance 0 7.407407407 3 20.40816327 3.5 28.57142857 4 45.45454545 4.5 76.92307692 5 111.1111111
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  • Spring '15
  • Dadabay
  • Chemistry, Reaction, Rate equation, crystal violet-sodium hydroxide

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