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Absorbance of light by a transition metal complex investigation

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Introduction

Stephanie Chan 12HT Chemistry HL - Mr. Fryer Absorbance of light by a transition metal complex investigation Introduction Commonly known as transition metals, d block elements have partially filled d sublevels in one or more of their oxidation states. It is in the first row of transition elements that the 3d sub-level is incomplete. These d block elements show certain characteristic properties such as multiple oxidation states, ability to form complex ions, coloured compounds and good catalytic properties. In terms of variable oxidation states, d block elements usually have a +2 oxidation number which corresponds to the loss of the two 4s electrons (as it is easier to lose the 4s electrons than the 3d electrons). Transition metals can have variable oxidation states because the ionization energies allow for up to two 3d electrons to be lost. Because transition metals are relatively small in size, the transition metal ions attract species that are rich in electrons - ligands (neutral molecules or negative ions that contain non-bonding pair of electrons - which when covalently bonded with and form complex ions. Because the d orbitals usually split up into two groups (high and low) in transition metal complex ions, the energy required to promote a d electron into the higher split level corresponds with a particular wavelength in the visible region, which is absorbed when light passes through the complex ion. ...read more.

Middle

Mix the solution thoroughly with a glass stirring rod, make sure the solution is transparent (not murky) and no remnants of the nickel sulphate should be present in the solution 4) Label the five 50cm� volumetric flasks: 0.03125mol, 0.0625mol, 0.125mol, 0.25mol and 0.5mol 5) Pipette 25cm� of the previously made nickel sulphate solution from the 250cm� beaker and place into volumetric flask labeled "0.5mol" 6) Pipette another 25cm� from the beaker and place into volumetric flask labeled "0.25mol" 7) Measure and pipette 25cm� of deionised water and add into "0.25mol" 8) Mix thoroughly 9) Measure and pipette 25cm� from "0.25mol" and add into "0.125mol" 10) Repeat steps 7 to 8 but add the water into "0.125mol" 11) Measure and pipette 25cm� from "0.125mol" and add into "0.0625mol" 12) Repeat step 10 but add into the water "0.0625mol" 13) Measure and pipette 25cm� from "0.0625mol" and add into "0.0313 mol" 14) Repeat step 10 but add into the water"0.0313mol" 15) Connect the PASPORT colorimeter to the computer 16) Select to measure red (660nm) absorbance 17) After all five solutions have been made, label five cuvettes the same labels as the volumetric flasks (place on lid, careful not to have any of the label on the cuvette itself) ...read more.

Conclusion

Evaluation One aspect I can improve my method is using the same cuvette and in the same direction each time for measuring all the different solutions, as it has been noted that the cuvettes we have been currently using are not perfectly constructed and may differ with the distance as light passes through. This will help improve the accuracy of the results and an important aspect to take into consideration, because also stated in the Beer-Lambert law, the length in which the light passes through also makes a difference in the absorption of light (the longer the container is, the more chances of light interacting with the molecules of the solution). Another aspect was in the preparing the different solutions, because I had diluted each solution using the same solutions from before, so the uncertainty of each would naturally continuously build up (final uncertainty of 4.31%) - for example, if I had accidentally created a 0.052 mol nickel sulphate solution, then the next solution I diluted from that solution would not be 0.025 mol as intended. One way to see through this limitation is to perhaps prepare each solution separately to avoid a build up of uncertainties. In addition, another way to make this investigation more conclusive and detailed could be increasing the different amounts of concentration of the nickel sulphate solution, as I only had 5 different concentrations. ...read more.

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