Report How Much A Chemical Substance Absorbs Light A Spectrophotometer
Discussion of Results and Scientific Explanation:
In order to observe how much a chemical substance absorbs light a spectrophotometer can be used. A spectrophotometer measures the amount of light absorbed by measuring the difference in the intensity of the light before and after a beam of light passes through a sample solution. The area in which light is absorbed can provide information about the molecule, such as the concentration, by identifying the most preferentially absorbed wavelength.1
Food coloring and potassium permanganate:
This method was used with red, blue, and purple food colorings and potassium permanganate. Wavelength measures energy in nanometers, from the top of one peak to the top of another peak, of a wave. Each wavelength …show more content…
has a different color that is transmits, therefore a change in wavelength will change the absorbency and transmittance as well, which means that either more or less of the wave will make it through the solution. 2
The color of the dyes, absorb all of the complementary color to the perceived color and the color we see is reflected and/or transmitted. The absorbed wavelength value would peak at the wavelength that is opposite of that of the reflected color, this means that if you have a solution that looks red, the absorbed wavelength would be green, since red and green are complementary, opposite, colors, as seen in the figure below. 3
So for a red solution the absorbance level would peak when a wavelength of around 525 nanometers was passed through it.
A wavelength of 525 nanometers is within the range for green which is the complementary color for red. The relation between absorbance and percent transmittance is inversely related and as such when absorbance is low then transmittance is high, and vice versa. This is given by the equation: A = 2 - log10 %T. Where A is absorbance and T is Percent Transmittance. Transmittance is the percent of light that travels through the sample. When transmittance is at its lowest, the corresponding wavelength is that of the complementary color of the displayed color. For the experiment conducted for this report, the last absorbance value measured at a wavelength of 600nm was where the blue solution was the highest. This is in coordination with the method explained above because the absorbance value should peak, be the highest, where the color is complementary. 600nm is within the wavelength that is orange, which is complementary to blue. The red solution peaked at 520nm for absorbance and this is also in accordance since 520nm is still within the spectrum for green. The purple solution made with dye spiked between 500nm and 530nm, however it can be seen that it starts increasing around 600nm where it raises up from 0.11 to 0.14 for absorbance level. This is a little bit unclear, however the purple should spike twice, once around the complementary color’s wavelength for each of the mixed dyes. Considering these experiments were done quickly the inaccuracy of getting a clear picture of where the two peaks were could have been because of multiple reasons. This could have been due to an unequal mixing of the two solutions, resulting in a change in the wavelengths that could be absorbed. This could also have been because we did not use a low enough wavelength, since there was not a true wavelength peak that was recorded for the blue solution. This is a good source
of error for not having a clear peak for purple. For this experiment this would have been around 520nm and 600nm. Finally, for potassium permanganate it peaked at 530nm, this makes sense since the color of the solution was a red tinted purple, making its complementary color being near yellow, but closer to green than it would be to orange. The purpose of this experiment was to become familiar with using a spectrophotometer as well as to find the analytical wavelength of potassium permanganate. An analytical wavelength is the corresponding wavelength to where a solution hits a maximum absorbance level and therefore a minimum percent transmittance. For this experiment iteration, the analytical wavelength value was at 530 nm. This was expected since, the solution was a red-purple color and 530nm is within the green spectrum. This wavelength was where the absorbance was the highest and this happens at the commentary color.
Potassium Permanganate Calibration Curve
The purpose of discovering the potassium permanganate calibration curve, was to identify the correlation between concentration, wavelength and absorbance and percent transmittance. was done at a wavelength of 530nm because this was the analytical wavelength. This was determined through the previous experiment by testing a known concentration across multiple wavelengths and discovering where absorbance was the highest and percent transmittance was the lowest. This would be the value the correlates to the analytical wavelength. The molar absorptivity constant given by the website is 2212 (mol L-1)-1 cm-1, the molar absorptivity that was discovered for this experiment was 1407.2 (L mol-1 cm-1). This discrepancy could have been because of incorrect dilutions which would give incorrect concentrations, or this could have been because of incorrect blanking of the machine. The y-intercept for the absorbance versus the concentration of the KMnO4 was -0.0684, this is because the absorbance level increases with a more concentrated solution. The y-intercept should be 0 because of Beers law, A=€bc+0. The value that we calculated, while below 0 was still within a tenth of 0, identifying that this value was close to Beers law. This could have been because of incorrectly measured dilutions and/or concentrations. A linear trend line was used for the absorbance vs concentration graph because mathematically Beers law identifies a linear relationship between absorbance and concentration, this trend line also gave the closest R2 value to 1, which means it was the closest fitting line for the give set of points. A logarithmic trend line was used for the percent transmittance versus concentration since the mathematical expression identifies the relationship to be logarithmic and once again this gave the closest R2 value to 1.3 The R2 measures how well the regression line fits the given data. The closer that this value is to one makes the regression line closer to actual line of correlation between the points. The R2 value was 0.9345 for both, which is fairly close to one, meaning our data is fairly accurate.
Phosphate Full Spectrum The purpose of running the phosphate full spectrum is to be able to determine the analytical wavelength for the phosphate. The struggles encountered while doing this were making sure the concentrations for each solution were correctly measured, and that the ammonium vanadomolybdate (AVM) to solution ratio were accurate. The analytical wavelength found by this experiment looks to be around 360 nm as this is where the absorbance level is the highest. This does make sense since the solution was colorless before the AVM was added, making the solution turn yellow, 360 nm is on the side of the spectrum that is below purple. Since yellow’s complementary color is purple this is the side where the absorbance level is expected to be the highest. AVM mixes with the phosphate in order to create a yellowish solution through a chemical reaction KH2PO4 + NH4VO3, this forms a vanadomolybdophosphoric acid which yellow color’s intensity if proportional to the phosphate concentration.4 Phosphate Calibration Curve The phosphate calibration curve was measure at 360nm, our analytical wavelength from when we ran the phosphate full spectrum actually was 350nm, however due to technical difficulties we had to change this wavelength up ten nanometers to receive a reading for the data. Another source identified the molar absorptivity to be 2.9×〖10〗^4 L Mol-1 cm-1 measured at 830 nm, with a 0.99 for an R2 value. Whereas ours was 5124 L Mol-1 cm-1 , which was the y-intercept of our line of best fit, with an R2 value of 0.7281, this R2 value is low enough to suggest an issue with our data itself, since the line of best fit is not close to the actual slope of the graph. The biggest outlier is at a concentration of 0.000101, the absorbance value is 0.5867 whereas at 0.0001 the absorbance level is only 0.316. The error in the creation of data could have been due to incorrect preparation of solutions, which would change the concentration level from that which we had calculated. Other issues could have involved further technical difficulties, trace solutions left in pipets mixing with the solution we were measuring and incorrect recording of data. Also, the other source of information measured at a wavelength of 830 nm which was at the opposite side of the spectrum from where we recorded our values.
Cola Analysis In order to identify the phosphate in the cola samples we used the phosphate calibration curve in order to identify what the concentration of phosphate was. We also had to utilize the skills we had learned on how to use a spectrophotometer in order to complete this part of the assignment as well as how to make dilutions and concentrations. The cola samples had to be diluted because they were too dark for the spectrophotometer to read, as this was the case the absorbance level would have been way to high and not give an accurate absorbance level that could be measured against our calibration curve. Also, since the cola is colored and the brown syrup could have prevented any light and wouldn’t have let the AVM in the phosphate be seen. AVM was added in order to color the phosphate molecules of the phosphoric acid because otherwise it would be impossible to measure the clear phosphate. The struggle in this part of the assignment was because of time constraints and mess ups, only one person was working on this part of the assignment, which would mean there was no double checking by another person to make sure the work was done correctly. The work done incorrectly could have been incorrect dilutions, AVM to solution ratio, measured at an incorrect wavelength on a different machine, and machine malfunctions. The only value that could be found online was for the concentration of phosphate in Cherry Cola and this was 66% phosphate however ours was 17% which was a huge difference that could amount to our calibration curve being messed up or the various errors that have been listed previously.
In order to observe how much a chemical substance absorbs light a spectrophotometer can be used. A spectrophotometer measures the amount of light absorbed by measuring the difference in the intensity of the light before and after a beam of light passes through a sample solution. The area in which light is absorbed can provide information about the molecule, such as the concentration, by identifying the most preferentially absorbed wavelength.1
Food coloring and potassium permanganate:
This method was used with red, blue, and purple food colorings and potassium permanganate. Wavelength measures energy in nanometers, from the top of one peak to the top of another peak, of a wave. Each wavelength …show more content…
has a different color that is transmits, therefore a change in wavelength will change the absorbency and transmittance as well, which means that either more or less of the wave will make it through the solution. 2
The color of the dyes, absorb all of the complementary color to the perceived color and the color we see is reflected and/or transmitted. The absorbed wavelength value would peak at the wavelength that is opposite of that of the reflected color, this means that if you have a solution that looks red, the absorbed wavelength would be green, since red and green are complementary, opposite, colors, as seen in the figure below. 3
So for a red solution the absorbance level would peak when a wavelength of around 525 nanometers was passed through it.
A wavelength of 525 nanometers is within the range for green which is the complementary color for red. The relation between absorbance and percent transmittance is inversely related and as such when absorbance is low then transmittance is high, and vice versa. This is given by the equation: A = 2 - log10 %T. Where A is absorbance and T is Percent Transmittance. Transmittance is the percent of light that travels through the sample. When transmittance is at its lowest, the corresponding wavelength is that of the complementary color of the displayed color. For the experiment conducted for this report, the last absorbance value measured at a wavelength of 600nm was where the blue solution was the highest. This is in coordination with the method explained above because the absorbance value should peak, be the highest, where the color is complementary. 600nm is within the wavelength that is orange, which is complementary to blue. The red solution peaked at 520nm for absorbance and this is also in accordance since 520nm is still within the spectrum for green. The purple solution made with dye spiked between 500nm and 530nm, however it can be seen that it starts increasing around 600nm where it raises up from 0.11 to 0.14 for absorbance level. This is a little bit unclear, however the purple should spike twice, once around the complementary color’s wavelength for each of the mixed dyes. Considering these experiments were done quickly the inaccuracy of getting a clear picture of where the two peaks were could have been because of multiple reasons. This could have been due to an unequal mixing of the two solutions, resulting in a change in the wavelengths that could be absorbed. This could also have been because we did not use a low enough wavelength, since there was not a true wavelength peak that was recorded for the blue solution. This is a good source
of error for not having a clear peak for purple. For this experiment this would have been around 520nm and 600nm. Finally, for potassium permanganate it peaked at 530nm, this makes sense since the color of the solution was a red tinted purple, making its complementary color being near yellow, but closer to green than it would be to orange. The purpose of this experiment was to become familiar with using a spectrophotometer as well as to find the analytical wavelength of potassium permanganate. An analytical wavelength is the corresponding wavelength to where a solution hits a maximum absorbance level and therefore a minimum percent transmittance. For this experiment iteration, the analytical wavelength value was at 530 nm. This was expected since, the solution was a red-purple color and 530nm is within the green spectrum. This wavelength was where the absorbance was the highest and this happens at the commentary color.
Potassium Permanganate Calibration Curve
The purpose of discovering the potassium permanganate calibration curve, was to identify the correlation between concentration, wavelength and absorbance and percent transmittance. was done at a wavelength of 530nm because this was the analytical wavelength. This was determined through the previous experiment by testing a known concentration across multiple wavelengths and discovering where absorbance was the highest and percent transmittance was the lowest. This would be the value the correlates to the analytical wavelength. The molar absorptivity constant given by the website is 2212 (mol L-1)-1 cm-1, the molar absorptivity that was discovered for this experiment was 1407.2 (L mol-1 cm-1). This discrepancy could have been because of incorrect dilutions which would give incorrect concentrations, or this could have been because of incorrect blanking of the machine. The y-intercept for the absorbance versus the concentration of the KMnO4 was -0.0684, this is because the absorbance level increases with a more concentrated solution. The y-intercept should be 0 because of Beers law, A=€bc+0. The value that we calculated, while below 0 was still within a tenth of 0, identifying that this value was close to Beers law. This could have been because of incorrectly measured dilutions and/or concentrations. A linear trend line was used for the absorbance vs concentration graph because mathematically Beers law identifies a linear relationship between absorbance and concentration, this trend line also gave the closest R2 value to 1, which means it was the closest fitting line for the give set of points. A logarithmic trend line was used for the percent transmittance versus concentration since the mathematical expression identifies the relationship to be logarithmic and once again this gave the closest R2 value to 1.3 The R2 measures how well the regression line fits the given data. The closer that this value is to one makes the regression line closer to actual line of correlation between the points. The R2 value was 0.9345 for both, which is fairly close to one, meaning our data is fairly accurate.
Phosphate Full Spectrum The purpose of running the phosphate full spectrum is to be able to determine the analytical wavelength for the phosphate. The struggles encountered while doing this were making sure the concentrations for each solution were correctly measured, and that the ammonium vanadomolybdate (AVM) to solution ratio were accurate. The analytical wavelength found by this experiment looks to be around 360 nm as this is where the absorbance level is the highest. This does make sense since the solution was colorless before the AVM was added, making the solution turn yellow, 360 nm is on the side of the spectrum that is below purple. Since yellow’s complementary color is purple this is the side where the absorbance level is expected to be the highest. AVM mixes with the phosphate in order to create a yellowish solution through a chemical reaction KH2PO4 + NH4VO3, this forms a vanadomolybdophosphoric acid which yellow color’s intensity if proportional to the phosphate concentration.4 Phosphate Calibration Curve The phosphate calibration curve was measure at 360nm, our analytical wavelength from when we ran the phosphate full spectrum actually was 350nm, however due to technical difficulties we had to change this wavelength up ten nanometers to receive a reading for the data. Another source identified the molar absorptivity to be 2.9×〖10〗^4 L Mol-1 cm-1 measured at 830 nm, with a 0.99 for an R2 value. Whereas ours was 5124 L Mol-1 cm-1 , which was the y-intercept of our line of best fit, with an R2 value of 0.7281, this R2 value is low enough to suggest an issue with our data itself, since the line of best fit is not close to the actual slope of the graph. The biggest outlier is at a concentration of 0.000101, the absorbance value is 0.5867 whereas at 0.0001 the absorbance level is only 0.316. The error in the creation of data could have been due to incorrect preparation of solutions, which would change the concentration level from that which we had calculated. Other issues could have involved further technical difficulties, trace solutions left in pipets mixing with the solution we were measuring and incorrect recording of data. Also, the other source of information measured at a wavelength of 830 nm which was at the opposite side of the spectrum from where we recorded our values.
Cola Analysis In order to identify the phosphate in the cola samples we used the phosphate calibration curve in order to identify what the concentration of phosphate was. We also had to utilize the skills we had learned on how to use a spectrophotometer in order to complete this part of the assignment as well as how to make dilutions and concentrations. The cola samples had to be diluted because they were too dark for the spectrophotometer to read, as this was the case the absorbance level would have been way to high and not give an accurate absorbance level that could be measured against our calibration curve. Also, since the cola is colored and the brown syrup could have prevented any light and wouldn’t have let the AVM in the phosphate be seen. AVM was added in order to color the phosphate molecules of the phosphoric acid because otherwise it would be impossible to measure the clear phosphate. The struggle in this part of the assignment was because of time constraints and mess ups, only one person was working on this part of the assignment, which would mean there was no double checking by another person to make sure the work was done correctly. The work done incorrectly could have been incorrect dilutions, AVM to solution ratio, measured at an incorrect wavelength on a different machine, and machine malfunctions. The only value that could be found online was for the concentration of phosphate in Cherry Cola and this was 66% phosphate however ours was 17% which was a huge difference that could amount to our calibration curve being messed up or the various errors that have been listed previously.