Reaction kinetics of aquation.docx - Experiment 10 Reacton...

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Experiment 10 : Reaction kinetics of aquation of pentaamminechlorocobalt (III) chloride Date : 03 November 2016 Name : Chan Yin Kuan, Mak Wei Ying Aim : To measure the rate of aquation and determine the rate constant of pentaamminechlorocobalt (III) chloride, [CoCl(NH 3 ) 5 ]Cl 2 at 60 Results and Calculation Calculation of A A = ε lC = 2.1 m 2 mol -1 x 1cm x 1.2 x 10 -2 mol dm -3 = 2.1 m 2 mol -1 x 1 x 10 -2 m x 1.2 x 10 -2 mol dm -3 = 0.021 m 3 mol -1 x 1.2 x 10 -2 mol dm -3 = 0.021 x10 3 dm 3 mol -1 x 1.2 x 10 -2 mol dm -3 = 0.252 where ε is the molar absorptivity of [Co(NH 3 ) 5 (H 2 O)] 3+ at 550 nm l is the length of optical cell C is the concentration of compound t (min) A (λ = 550nm) A t - A ln (A t - A ) 0 0.469 0.217 -1.528 10 0.429 0.177 -1.732 20 0.409 0.157 -1.852 30 0.391 0.139 -1.973 40 0.384 0.132 -2.025 50 0.386 0.116 -2.154 60 0.352 0.100 -2.303
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70 0.339 0.087 -2.442 80 0.332 0.080 -2.526 90 0.322 0.070 -2.659 Graph of ln (A t - A ) against t 0 10 20 30 40 50 60 70 80 90 100 -3 -2.5 -2 -1.5 -1 -0.5 0 f(x) = - 0.01x - 1.58 Graph of (ln At - A) against t t (min) ln (At - A) Calculation of rate constant, k From the slope of the plot, in first order reaction, ln C o C t = kt Spectroscopically, in terms of absorbance, ln A o A A t A = kt ln ( A o A ) – ln ( A t A )= kt - ln ( A t A ¿ = kt - ln ( A o A ) ln ( A t A ¿ =− kt + ln ( A o A )
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By comparing equation ln ( A t A ¿ =− kt + ln ( A o A ) and y = -0.012x – 1.5792, Therefore, rate constant, k is 0.012 min -1 . Discussion Derivation of equation [Co(NH 3 ) 5 Cl] 2+ + H 2 O [Co(NH 3 ) 5 (H 2 O)] 3+ + Cl - Consider the reaction follows the first order kinetics reaction, Rate of reaction: - d dt [Co(NH 3 ) 5 Cl] 2+ = k [Co(NH 3 ) 5 Cl] 2+ Let concentration of [Co(NH 3 ) 5 Cl] 2+ be c.
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