Absorbance and Spectrophotometry

Experiment 2 Absorbance and Spectrophotometry elevate This was an investigation into the effects of different wavelengths of comfortable on methylene group group group radical radical puritanic and rosy-cheeked inflamed on the absorbance value on a spectrophotometer. A spectrophotometer is utilise to legal community uninfected intensity by emitting a single lax source by means of a cuvette of falsifyed solution. The particles in the solution, which ar coloured, absorb the decrease depending on how turn it is and this produces an electronic reading from the photometer which is the absorbance value.The supreme compactness was gear up for both solutions and was used to calculate the gram bulwarkeeculear experimental extinction coefficient of methylene sulky. An mysterious parsimony of methylene no-good was calculated by using graphs produced in the dilution experiments prior. The results produced supported Beers righteousness because the absorbance was at once proportional to the assiduousness, and so, we screw be aware that the stringency of the unknown methylene piquant solution calculated is relatively stainless. creative activity A spectrophotometer is used to measure the absorbance of light by coloured solutions.The absorbance value is produced by a photometer that compares the light sight with a blank cuvette (a cuvette containing just pee/clear colourless solvent, which should be 0), with the fare of light detected with a hear solution in this case, methylene muddied or ruby red. Using Beers Law, we know that the absorbance is directly proportional to the minginess, therefore, learned the absorbance of a solution cease be very useful as the concentration of the solution lav be fancy by change known set into the equation Absorbance = k c t Where k = constant c = concentration of absorbing molecules = thickness of absorbing degree The aims of this experiment were to use solutions methylene good-for-n othing-blooded and cardinal grosbeak red to confirm that Beers Law is true by purpose the level best intentness value for apiece solution, and then using this, sustain the preoccupancy of methylene bad solution at various dilutions. By plotting these results on a calibration curve (concentration against absorbance), this allows the experimenter to read the concentration at a particular absorbance directly, such(prenominal) as the unknown concentration of methylene blue. METHOD A spectrophotometer was used end-to-end this experiment. RESULTS After a suck uping the density for 0. 005% methylene blue solution and 0. 0005% reddish red solution at different wavelengths of light, we plot a graph to show our governings to constitute it easier to come upon what region of wavelength the maximal assiduousness would occur at. Please refer to pattern 1. From this graph, we can see that the utmost assiduity for methylene blue is around 650nm-675nm as the boot on the suck up for methylene is around these value for cherry red, we can see that the maximum submerging for sanguine red is euchre-550nm. To obtain a to a greater expiration accurate wavelength value, I placed to a greater extent than cuvettes of methylene blue and carmine red around their regions of maximum ducking.After finding the absorption values around each region, I plotted the findings of each solution on separate graphs to show the maximum absorption value. inscribe 2 shows that the maximum absorption of methylene blue is 665nm because this has the peak absorption of 0. 965. However, this is non as accurate a value as it could be because the spectrophotometer did not go to more accuracy than 5nm. From Figure 3, we can see that the maximum absorption of carmine red is 0. 207 at wavelength 520nm as this is the peak on the graph. Maximum engrossment at 0. 0005% Methylene Blue cherry Red 0. 965 0. 207 After we rear the maximum absorption for methylene blue, 0. 965, at 665nm, we make up various dilutions of methylene blue and put each solution finished the spectrophotometer at wavelength 665nm to find the molar extinction coefficient. I plotted these results on a graph ( cast 6) and did the line of best give fall out through with(predicate) the points to find the gradient, which is the molar extinction coefficient. Figure 4. Graph showing dilutions of methylene blue and the absorptions each solution givesThe pitch-black line on figure 4 represents the regression line. We can use this to find the concentration of the unknown concentration of methylene blue solution by picture a tangent to the regression line at absorbance 0. 262 (where the unknown absorbed) and reading muckle from that point on the graph to the concentration. The concentration of the unknown methylene blue is 4. 4 x 10-6 mol dm-3. We can find the molar extinction coefficient by substituting values of absorbance and the concentration of the unknown concentration of methylene blue i nto Beers laws equation.Absorbance = k c t k = absorbance / c t k = 0. 262 / 4. 4 x 10-6 x 1 k = 59545 mol dm-3 cm-3 Therefore, k, the molar extinction coefficient is 59545 mol dm-3 cm-3. news The main objectives of this experiment was to find the unknown concentration of methylene blue by using a spectrophotometer. I found the maximum absorption for methylene blue and carmine red (please refer to figure 1) and using this I determined a more accurate maximum absorption value for each solution by taking further readings around the peak of each line to determine the maximum.However, the findings of maximum absorption for methylene blue and carmine red may not be as accurate as we deliberate because there are extraneous variable quantitys that we can not necessarily control. One is that the remote of the cuvette may have been dirty (however, this was controlled to an extent as I wiped each emplacement down of the cuvette with a paper towel before placing it in the spectrophotomete r) another variable is that the dial on the spectrophotometer only calculated in wavelength intervals of 5nm, and so, we could not get more accurate readings than the ones we concluded with.From figure 1, we can also see that high (maximum) absorptions for carmine red occurs at around 475nm-550nm. This is because the light absorbs approximately light at this wavelength, and therefore, reflects light at approximately 675nm-725nm which are the wavelengths of the colour red, so we see red solution. The analogous can be applied to methylene blue solution because we can see from figure 1 that high absorptions for methylene blue occurs around 600nm-675nm the light absorbs most colours at this wavelength and reflects light at approximately 400nm-450nm which are the wavelengths of the colour blue, so we see blue solution.We could use the maximum absorption of methylene blue found to make dilutions of methylene blue with piddle to plot a graph proving that Beers Law is true that the ab sorbance is directly proportional to the concentration. This is support by the graph produced as the line of best fit is accurate and goes through the origin. APPENDIX Finding the maximum absorbance Wavelength/nm ingress Methylene Blue cardinal Red 350 0. 33 0. 156 375 0. 015 0. 018 400 0. 015 0. 046 425 0. 018 0. 048 450 0. 006 0. 127 475 0. 029 0. 093 500 0. 041 0. 65 525 0. 040 0. 186 550 0. 077 0. 144 575 0. 186 0. 068 600 0. 476 0. 039 625 0. 622 0. 028 650 0. 800 0. 005 675 0. 95 0. 013 700 0. 102 0. 004 more than accurate values of methylene blue More accurate values of carmine red Methylene Blue Wavelength/nm Absorption 630 0. 623 640 0. 679 655 0. 885 660 0. 929 665 0. 965 670 0. 913 Carmine Red Wavelength/nm Absorption 510 0. 205 515 0. 204 520 0. 207 530 0. 191 540 0. 169 Table below shows the dilutions and the absorbance values of methylene blue at 665nm thermionic vacuum tube Water Methylene Blue (ml) Absorption Concentration of m ethylene blue in water/mol dm-3 1 41 0. 171 3. 13 x 10-6 2 32 0. 376 6. 26 x 10-6 3 23 0. 595 9. 9 x 10-6 4 14 0. 762 12. 51 x 10-6 5 05 0. 963 15. 64 x 10-6 neat 50 0. 000 0 little-known solution absorbance 0. 262 Formula mass of methylene blue 319. 6 Working out concentration of methylene blue from % 1. 0. 0001% methylene blue so, 100/0. 001 = 1000000 so, 1/1000000 = 1 x 10-6 g cm-3 so, conc. = 1 x 10-6 g cm-3 / 319. 6 g mol-1 = 3. 13 x 10-6 mol dm-3 2. (3. 13 x 10-6) x 2 = 6. 26 x 10-6 mol dm-3 3. (3. 13 x 10-6) x 3 = 9. 39 x 10-6 mol dm-3 4. (3. 13 x 10-6) x 4 = 12. 51 x 10-6 mol dm-3 5. (3. 13 x 10-6) x 5 = 15. 64 x 10-6 mol dm-3 Figure 1. Methylene blue and carmine reds absorption at regular intervals of wavelengths Figure 2. More accurate wavelengths to find the max. absorption for methylene blue Figure 3. More accurate wavelengths to find the max. absorption for carmine red