Purpose
The purpose of this experiment is to find the pKIn blue using spectrophotometry. Bromophenol blue dissociate in water by the following reaction:
i) HIn + H2O ⇋ H3O+ + In-
The KIn value can be calculated from the reaction: ii) K_In=[H3O+][ In-]/[HIn]
Taking the negative logarithm on both sides, iii)〖pK〗_In=pH+log[HIn]/[〖In〗^- ]
Solution sample of bromophenol blue with different but similar pH is put into spectrophotometer to find out the ratio of [HIn]/[In-] based on the Beer- Lambert Law1: iv) A=log(l_t/l_o )
Where A is the absorbance of the sample, lt is the intensity of light passed through the solution and lo is the intensity of light before passing through the solution, which is the same for the same spectrophotometer. …show more content…
From the absorbance of sample A3 and B3 and their diluted versions, the following graphs can be drawn: Figure 2- A graph showing the relation between concentration of bromophenol blue in M and their absorbance for the acidic form of the molecule, showing the molar absorptivity constant of the molecule at wavelengths 440 nm and 590 nm.
The reading with concentration 6 x 10-4 M at wavelength 440 nm was discarded as it is too off from the trend line that it is not following the trend at all. The deviated reading may be caused by the cross contamination when using the same cuvette to measure the absorbance for a more concentrated solution, then a more diluted solution, even with rinsing in between.
Figure 3- A graph showing the relation between concentration of bromophenol blue in M and their absorbance for the basic form of the molecule, showing the molar absorptivity constant of the molecule at wavelengths 440 nm and 590 …show more content…
The molar absorption constants were found to be: 358 for the acid form at wavelength 440 nm, 12 for the acidic form at wavelength 590 nm, 64.0 for the basic form at wavelength 440 nm and 558 for the basic form at wavelength 590 nm. Some of the R2 values are off from the ideal value of 1, while some datum were discarded as it did not make sense. Both parts are not very accurate and precise, due to the large range of readings that the spectrophotometer were showing, and the readings never steadied, therefore could not get a very accurate
The purpose of this experiment is to find the pKIn blue using spectrophotometry. Bromophenol blue dissociate in water by the following reaction:
i) HIn + H2O ⇋ H3O+ + In-
The KIn value can be calculated from the reaction: ii) K_In=[H3O+][ In-]/[HIn]
Taking the negative logarithm on both sides, iii)〖pK〗_In=pH+log[HIn]/[〖In〗^- ]
Solution sample of bromophenol blue with different but similar pH is put into spectrophotometer to find out the ratio of [HIn]/[In-] based on the Beer- Lambert Law1: iv) A=log(l_t/l_o )
Where A is the absorbance of the sample, lt is the intensity of light passed through the solution and lo is the intensity of light before passing through the solution, which is the same for the same spectrophotometer. …show more content…
From the absorbance of sample A3 and B3 and their diluted versions, the following graphs can be drawn: Figure 2- A graph showing the relation between concentration of bromophenol blue in M and their absorbance for the acidic form of the molecule, showing the molar absorptivity constant of the molecule at wavelengths 440 nm and 590 nm.
The reading with concentration 6 x 10-4 M at wavelength 440 nm was discarded as it is too off from the trend line that it is not following the trend at all. The deviated reading may be caused by the cross contamination when using the same cuvette to measure the absorbance for a more concentrated solution, then a more diluted solution, even with rinsing in between.
Figure 3- A graph showing the relation between concentration of bromophenol blue in M and their absorbance for the basic form of the molecule, showing the molar absorptivity constant of the molecule at wavelengths 440 nm and 590 …show more content…
The molar absorption constants were found to be: 358 for the acid form at wavelength 440 nm, 12 for the acidic form at wavelength 590 nm, 64.0 for the basic form at wavelength 440 nm and 558 for the basic form at wavelength 590 nm. Some of the R2 values are off from the ideal value of 1, while some datum were discarded as it did not make sense. Both parts are not very accurate and precise, due to the large range of readings that the spectrophotometer were showing, and the readings never steadied, therefore could not get a very accurate