分光光度计法测定甲基红离解常数 实验数据处理.doc

V、Data treatment Part 1：Measure the maximum absorptionTable 1: Absorption of solution AWavelength/nmabsorption4200.0754400.1724600.414800.7625001.145101.2865201.3535301.3325401.2635600.9055800.2956000.046 Graph 1: Absorption of solution AConclusion：from the Graph 1，we can get the wavelength for the maximum absorption of solution A is 520 nm. Table 2: Absorption of solution B Wavelength/nmabsorption4100.524200.5434300.5524400.5524500.544600.4984800.3545000.1785200.0745400.037Graph 2: Absorption of solution BConclusion：from the Graph 2，we can get the wavelength for the maximum absorption of solution A is 430-440 nm. Part 2：Test the Beers lawTable 3: Absorption of HMR in different concentrationsNo.(concentration)Absorption (520nm )Absorption (430nm )0#-c(A)1.3530.1471#-0.75c(A)1.0640.1062#-0.5c(A)0.680.0643#-0.2c(A)0.3730.055Note：because it is always acidic through the process, we can ignore the absorotion of MR-.Graph 3：Absorption of HMR in different concentrations（520nm )(the forth data is ignored due to its large derivation)Graph 4：Absorption of HMR in different concentrations（430nm )Conclusion：(C0=1.851*10-5) from the Graph 3，the slope is 1.2510, so HNM520=1.2510/(C0=1.851*10-5)=6.79*104，from the Graph 4，the slope is 0.166, so HNM430=0.166/(C0=1.851*10-5)=8.97*103 .Table 4: Absorption of MR- of different concentrationsNo.(concentration)Absorption (520nm )Absorption (430nm )0#-c(B)0.0740.5521#-0.75c(B)0.04550.2882#-0.5c(B)0.04790.1343#-0.2c(B)0.03220.064Note：because it is alkaline through the process, we can ignore the absorotion of HMR.(the second data is ignored due to its large derivation)Graph 5：Absorption of MR- in different concentrations（520nm )(the forth data is ignored due to its large derivation)Graph 6：Absorption of MR- in different concentrations（430nm )Conclusion：(C0=1.851*10-5) from the Graph 5，the slope is 0.052, so NM-1520=0.052/(C0=1.851*10-5)=2.81*103，from the Graph 6，the slope is 0.836, so NM-1430=0.836/ (C0=1.851*10-5)=4.52*104.Part 3：the ratio VS the pH：to get the kTable 5: Absorption for the ratio VS the pHNo.（pH is different）Absorption (520nm )Absorption (430nm )ratio(MR-/HMR)lg(MR-/HMR)pHpK7#0.0240.0564.0998878630.6127719784.684.0672288#0.0410.0682.7778981060.4437163124.363.91628379#0.0550.051.4474525690.1606043413.973.809395710#0.080.0470.916005775-0.0381017883.693.7281018Note：the ratio(MR-/HMR) is calculated from pK= pH - lg(MR-/HMR) Conclusion：so the average number of pK is 3.8803 then we get the k=1.317*10-4VI、Question and Discussion Q1：Would the measurement results be influenced by the temperature？how to avoid or minimize the influences？Answer：Yes, for the reason that the k value of the methyl red will be changed with the temperature, which will also result in the change of the ratio of (MR-/HMR) and the measurement of the absorption. So we should measure all the data at the same temperature to minimize the influences. Q2：Can we still use the similar method to measure the equilibrium coefficient if the sample solution is colorless ？Answer：Yes, this method is not limited in the visible light area, it can also be used in the area of UV and IR areas for the reason that it is determined by the inter structure and interaction of substances. It also presents absorption in the area of UV and IR. Q3：Would it affect the measurement results if the solution volumes are not accurately pipetted when you are preparing solutions 7#-10#？Answer : There is no influences on the final results. According to the equation pK= pH - lg(MR-/HMR), the value MR-/HMR corresponds to a Ph value, so the pK wont be changed if the solution volumes are not accurately pipetted. D1: According to literature, the value pk of methyl red at the room temperature is about 5.05, however, we get 3.8803. Here are some reasons which may contribute to the deviation： The temperature，which has been talked about in Q1. The preparation of solution in A and B may also result the error, we should let one student to do the all pipettation and each time we should wish the pipette and any glass container with the solution. The errors comes from equipment, eg. We cannot get the total monochromatic light. Actually, the Beers law just applies to the dilute solutions, it may also cause some errors. We ignore the volume change when we prepare solutions of different concentrations. It will also cause some error because the volume cannot be just added without the consideration of volume change. The fresh prepared solution should be placed for a period to let the solution turn uniform. We also ignore the ignore the absorotion of HMR and MR-1 in the