Determination of the Reaction Order and Rate Constant for the Reaction of Malachite Green with Hydroxyl Ions Essay

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Determination of chemical equilibrium by absorption in the visible region (Fe+3 /SCN System) David KiesseLukwamusu DT203/2 14 Oct 13 Lab Partner: Christiana Poopola Aim: The aim of this experiment is to determine the equilibrium of a compound by using absorption spectrophotometry in the visible region. Procedure: Iron nitrate solution (Fe (NO₃)₃, 0.0166M) and potassium thiocyanate (KSCN, 0.004M) were mixed first together and then with HNO₃ (0.1M) and water in different proportions and solutions. Four solutions were prepared differently as follow: ① Fe(NO₃)₃ (40ml, 0.0166M) was mixed with KSCN (2ml, 0.004M) and three other solution. The equilibrium mixture was made up as follow: Compound | Concentration(M) | Solution A (ml) | Solution B(ml) | Solution C ( ml) | HNO₃ | 0.1 | 25 | 25 | 25 | (FeNO₃)₃ | 0.0166 | 2.5 | 2.5 | 5 | KSCN | 0.004 | 2.5 | 5 | 20 | | | 100 | 100 | 100 | A UV / visible spectra of each solution prepared was recorded with a Shimadzu UV 1601 using PMMA cells to contain the sample. Spectra were collected over the wavelength range 350nm to 800 nm and the absorbance recorded for the peaks observed are detailed in the table below: Results: Solution | Wavelength (nm) | Absorbance | ① | 455 | 0.178 | A | 459 | 0.015 | B | 459 | 0.040 | C | 456 | 0.339 | | | | SCN⁻ initial = (2ml/42ml) x 0.040 M = 1.9 x 10⁻⁴M 1-Calibration: A | FeSCN (M) | Ɛ | 0.178 | 1.9 x 10⁻⁴ | 938.84 | 2- Experiment: Sample | Absorbance | [FeSCN]eq | [Fe+3] eq | [SCN⁻]eq | K | A | 0.015 | 1.6x10⁻⁵ | 3.99x10⁻⁴ | 8.4x10⁻⁵ | 477.4 | B | 0.040 | 4.27x10⁻⁵ | 8.14x10⁻⁴ | 1.57x10⁻⁴ | 333.6 | C | 0.339 | 3.62x10⁻⁴ | 8.3x10⁻⁴ | 4.38x10⁻⁴ | 959.5. |

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