Absorbance of light by a transition metal complex investigation Essay

IntroductionComm solitary(prenominal) known as passing alloys, d block elements reach partially filled d sublevels in one or more of their oxidation states. It is in the root row of transition elements that the 3d sub-level is incomplete. These d block elements show received characteristic properties such as multiple oxidation states, ability to row labyrinthine ions, colou expiration compounds and good catalytic properties. In terms of covariant oxidation states, d block elements usually have a +2 oxidation number which corresponds to the loss of the two 4s negatrons (as it is easier to lose the 4s electrons than the 3d electrons). vicissitude coats can have variable oxidation states because the ionization energies al suck up for up to two 3d electrons to be lost.Because transition metals are relatively vitiated 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 elec trons 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 wave aloofness in the visible(a) region, which is absorbed when send passes through the complex ion. Transition metal usually then exhibits the remaining energy/ get down the complementary colour.In this investigation, the polar absorbance of these coloured closures pull up stakes be investigated by varying the number of moles of the transition metal in the theme. According to the Beer-Lambert constabulary, absorbance is direct proportional to the closeness and that thither is a logarithmic dependence betwixt the absorbance and the denseness of the substance, this relationship is as shown in figure 1 and 2.In the graph representation of the Beer-Lambert law, the logarithmic relationship can evidently be come upn as the concentration of the response increases, the calibration curve becomes less linear and more flat. This is probably due to the saturation of colour of the resultant role. In comeition, the graph also indicates that the relationship surfaces at the origin and is generally linear at lower concentrations.In this investigation, plate note (II) Sulphate provide be used as the transition metal and H2O will be used as the ligand. The complex ion organise will therefore be a hexaaqua plate note(II) complex ion, Ni (H2O) 6 2+. It has a coordination number of 6 and is of an octahedral shape. (Microsoft Encarta, 2007)AimTo investigate how the concentration of hexaaquanickel(II) ions (Ni (H2O) 6 2+) in dissolvent affects the absorbance of red light (660nm) by measuring rod it with a colorimeter.HypothesisAs the concentration of hexaaquanickel(II) ions increases, the absorbance of red light1 will also increase. This is so because as stated in the Beer-Lambert law, the a bsorbance of light is directly proportional to the concentration. Furthermore, as the concentration increases, there are more molecules of the complex ions within the solution to interact with the light that is being transmitted and so an increased absorbance at higher concentrations. In addition, despite the logarithmic relationship, I expect my selective information to show a linear relationship instead because the number of moles I am measuring red absorbance against is rather low (maximum 0.5 moles), so while it would be insufficient to see the clear logarithmic curve the linear increase in the beginning would still be evident.VariablesIndependent Concentration of hexaaquanickel(II) ions (0.0313mol, 0.0625mol, 0.125mol, 0.250mol, 0.500mol)Dependent Absorbency of red light (660nm)Controlled Volume of solution (25cm per disaccordent mol solution)EquipmentMethod1) Measure 6.57g of nickel sulphate with an electronic balance and lead in a 250cm beaker2) Measure 50cm of deion ised weewee with 50cm measuring cylinder and pour into the 250cm beaker with the nickel sulphate to create a 0.5mol nickel sulphate solution3) Mix the solution thoroughly with a ice rink stirring rod, make sure the solution is transparent (not murky) and no remnants of the nickel sulphate should be present in the solution4) Label the basketball team 50cm volumetric flasks 0.03125mol, 0.0625mol, 0.125mol, 0.25mol and 0.5mol5) Pipette 25cm of the previously made nickel sulphate solution from the 250cm beaker and place into volumetric flask stigmatiseed 0.5mol6) Pipette another 25cm from the beaker and place into volumetric flask label 0.25mol7) Measure and pipette 25cm of deionised water and add into 0.25mol8) Mix thoroughly9) Measure and pipette 25cm from 0.25mol and add into 0.125mol10) Repeat go 7 to 8 but add the water into 0.125mol11) Measure and pipette 25cm from 0.125mol and add into 0.0625mol12) Repeat step 10 but add into the water 0.0625mol13) Measure and pipette 25cm from 0.0625mol and add into 0.0313 mol14) Repeat step 10 but add into the water0.0313mol15) Connect the PASPORT colorimeter to the computer16) learn to measure red (660nm) absorbance17) 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)18) encounter one by one labeled cuvette with its corresponding volumetric flask label with a dropper19) Fill the remaining unlabeled cuvette with water20) Place the cuvette with water into the colorimeter and hale green button to calibrate, do not do anything until the green light switches off by itself21) Place the cuvette labeled 0.03125mol into the colorimeter press start and stop after getting a constant reading22) book of account the data23) Repeat steps 21-22 until all labeled cuvettes have been calculated for red absorbanceData TableConcentration / mol dm-Red light (660nm) absorbanceUncertaintiesUncertainties ( cm3)Measuring cylinder1.0cmBulb pipette0.06 cmElectronic urge on0.01gConcentration (mol/dm)UncertaintyGraphsDiscussion and ConclusionIt can be seen from the graph that there is a linear relationship between the metre of red light absorbed and the concentration of hexaaquanickel(II) ions. It can also be deduced that as the concentration increases, the red light absorption increases at double the rate. However, it is interesting to note that the line of dress hat fit does not start at the origin, but at (0, 0.0623) as the equation derived from the line of best fit states, suggesting that despite showing a clear linear trend, my data is precise but not accurate. This is possibly due to equipment imperfection, for example the cuvette, which will be discussed in the evaluation.However, it is still evident that, as stated in my hypothesis, as the concentration increases, the chances of light interacting with the complex ion molecules also increase, hence tame a higher light (red, in t his case) absorption. While it is true that the Beer-Lambert law states the relationship between concentration of a substance and its absorbency has a logarithmic relationship, my data is linear because the concentrations of my tested solutions were rather low, so if I were to stretch out my experiment and create more concentrated nickel sulphate solutions, I would expect to see the curve become non-linear as concentration increases because the solution will eventually become saturated. Therefore, in conclusion, my hypothesis corresponds with the results the relationship between red absorbance and concentration of hexaaquanickel(II) ions is quite clear as the concentration increases, the red absorbance also increases.EvaluationOne expression I can change my method is utilize 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 diff er with the distance as light passes through. This will help improve the trueness 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 figure 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 behavior 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 d etailed could be change magnitude the different amounts of concentration of the nickel sulphate solution, as I only had 5 different concentrations.BibliographyClark, J. (2007). The Beer-Lambert law. In Absorption spectra. Retrieved January 15, 2008, fromhttp//www.chemguide.co.uk/analysis/uvvisible/beerlambert.htmlMicrosoft(r) Encarta(r) Online Encyclopedia. (2007). Complex. Retrieved January 17, 2008, fromhttp//au.encarta.msn.com/encyclopedia_781538720/Complex.htmlNeuss, G. (2007). Determining the concentration of an element. In Chemistry course companion (p.276). Oxford University Press.1 Because nickel sulphate solution is green in colour, red light will be used to measure the absorbency of the solution as it is the complementary colour.