human
Give me essay about experiment was to determine the pKa of an acid-base indicator, Bromocresol Green, using spectrophotometry. Give me #Figure 4. Graph of Absorbance at 619nm of the second derivative where pH is in the X-axis and Absorbance in the Y-axis. only.
assistant
Based on Figure 4, the inflection point is at the pH” of 4.5. At this point, pH” = pKa, hence the pKa, is also 4.5.
Buffer 1 is the most acidic. The molar absorptivity at Hln is:
human
#Figure 1. Graph of Absorbance at 444nm of the first derivative where pH is in the X-axis and Absorbance in the Y-axis.
assistant
human
How about a    + 0.0423 = 0.47Hln section.
assistant
human
How about a    + Equation 5: section. End with the words 'The molar absorptivity'.
assistant
+ 0.0152 = ε x 1 [0.95]
   + ε=0.016
Buffer 8 is the most basic. The molar absorptivity at Hln is:
human
Give me Summary section.
assistant
The application of spectrophotometric titration allowed the pKa of Bromocresol Green to be determined. Two methods of analysis (graphical and additivity of Beer’s Law) were employed and generated results with good similarity. The isosbestic point was also determined. In comparison, the first method proved to be more accurate than the second.
human
Swap the first and the last sentence.
assistant
In comparison, the first method proved to be more accurate than the second. Two methods of analysis (graphical and additivity of Beer’s Law) were employed and generated results with good similarity. The isosbestic point was also determined. The application of spectrophotometric titration allowed the pKa of Bromocresol Green to be determined.
human
Give me #Spectrophotometric Determination of the pKa of an Acid-Base Indicator Report section.
assistant
human
Solutions
assistant
Disodium Phosphate Solution, 0.20 M. Dissolve the calculated amount of anhydrous disodium phosphate, Na 2 HPO 4 , or disodium hydrogen phosphate heptahydrate, Na 2 HPO 4 ·7H 2 O, in about 200 mL of distilled water and dilute to the mark in a 250 mL volumetric flask.
 * Citric Acid, 0.10 M. Dissolve the calculated amount of citric acid monohydrate about 200 mL of distilled water and dilute to the mark in a 250 mL volumetric flask.
 * Bromocresol Green Indicator. Crush and mix 0.1000 g (exact mass is needed in order to calculate the concentration) of bromocresol green indicator with 14.3 mL of 0.010 M NaOH in a mortar. Transfer to a 250 mL volumetric flask and dilute to volume with distilled water.
 * Buffer 1. Add 9.50mL of stock 0.1M citric acid solution to 0.50mL of stock 0.20M disodium phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 2. Add 8.00mL of stock 0.1M citric acid solution to 2.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 3. Add 6.00mL of stock 0.1M citric acid solution to 4.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 4. Add 5.50mL of stock 0.1M citric acid solution to 4.50mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 5. Add 5.00mL of stock 0.1M citric acid solution to 5.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 6. Add 4.00mL of stock 0.1M citric acid solution to 6.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 7. Add 2.00mL of stock 0.1M citric acid solution to 8.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 8. Add 0.50mL of stock 0.1M citric acid solution to 9.50mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
human
Give me  * Equation 9: section.
assistant
+ 0.5003 = 0.73[ln-] + 0.26 × 0.09
   + 0.5003 – 0.0234 = 0.73[ln-]
human
Give me Introduction section.
assistant
Acid-base indicators are used to show the end-points of acid-base reactions. Most acid-base indicators, including bromocresol green, are regarded as weak acids. The indicator is a complex molecule that can be represented with the formula Hln, where ln- represents the anion. When applied to low concentrations, the indicators signal pH changes within a particular range, which is variable among the indicators. The color change depends on the relative acid strength (pKa) of the conjugate acid form of the indicator. The formula below shows how weak acids ionize in aqueous solutions:
human
Give me #Figure 3. Graph of Absorbance at 619nm of the second derivative where pH is in the X-axis and Absorbance in the Y-axis. section.
assistant
human
How about a Instrumentation section.
assistant
ThermoFisher Evolution Array Spectrophotometer
 * pH meter
human
Give me Reagents section.
assistant
Disodium Phosphate Solution, Na 2 HPO 4, 0.20 M
 * Citric Acid, C₆H₈O₇, 0.10 M
 * Bromocresol Green Indicator, C 21 H 14 Br 4 O 5 S.
human
* Equation 2
assistant
Equation 2 can also be represented as:
   +
human
* Equation 4:
assistant
+ 0.25 =ε x 1 [0.95]
   + ε=0.26
human
Give me  * Equation 3 section.
assistant
The ratio of the indicator concentration is controlled by the pH of the solution, while the solution pH controls the ratio of the buffer concentration. The pH of a solution is measured using a pH meter.
Aside from using a pH meter, Ka can also be determined spectrophotometrically by employing Beer Lambert’s law. According to the law, for substances to absorb light within the visible region of the electromagnetic spectrum, the absorbance or the amount of light absorbed is directly proportional to the molar concentration (1). This experiment aims to determine the pKa of an acid-base indicator, Bromocresol Green, using spectrophotometery.
Wenzel, T. (2018). Beer’s Law.
human
Add another sentence about Consequentially, examined.
assistant
The ratio of the indicator concentration is controlled by the pH of the solution, while the solution pH controls the ratio of the buffer concentration. The pH of a solution is measured using a pH meter. 
Aside from using a pH meter, Ka can also be determined spectrophotometrically by employing Beer Lambert’s law. According to the law, for substances to absorb light within the visible region of the electromagnetic spectrum, the absorbance or the amount of light absorbed is directly proportional to the molar concentration (1). Consequentially, the absorption curve of an indicator at various pH levels can be examined to determine the Ka of the indicator. This experiment aims to determine the pKa of an acid-base indicator, Bromocresol Green, using spectrophotometery. 
Wenzel, T. (2018). Beer’s Law.
human
Give me Experimental section.
assistant
human
Give me Results and Discussion section.
assistant
Absorbance measurements were performed using a Thermo Scientific Evolution Array Spectrophotometer in the wavelength range between 400 and 800 nm. Plots of absorbance against λ for the bromocresol green indicator in buffers with different pH levels are illustrated in Figures 1, 2, 3 and 4.
human
Give me  * Equation 8: section.
assistant
+ 0.1153 = 0.73 (0.1 – [Hln]) + 0.26 x 1[Hln]
   + 0.1153 = 0.073 – 0.73 Hln + 0.26Hln
human
How about a Procedure section.
assistant
The procedure listed in the Instrumental Methods of Analysis Chem 447 of the Winter 2021 laboratory manual was followed.
Eight buffer solutions were prepared from varied concentrations of the phosphate and citric acid solutions. Bromocresol Green indicator solution was then added to each buffer and then cuvettes containing the solutions placed in the spectrophotometer to measure their absorbance wavelength.
human
Add another sentence about measured, recorded.
assistant
The procedure listed in the Instrumental Methods of Analysis Chem 447 of the Winter 2021 laboratory manual was followed. 
Eight buffer solutions were prepared from varied concentrations of the phosphate and citric acid solutions. The pH of the buffer solutions was then measured distinctly using a pH meter and recorded. Bromocresol Green indicator solution was then added to each buffer and then cuvettes containing the solutions placed in the spectrophotometer to measure their absorbance wavelength.
human
Give me    + [ln-] = 0.65 section.
assistant
Ka = [0.65][0.0458]/0.09 = 0.33
pKa = 5.322 – log [0.65]/[0.09] = 4.46
The pKa value is essential and unique to every indicator. In this experiment, two methods were employed to determine pKa. The first method revolved around measuring the pH of the buffer solutions and determination of the absorbance. From the results, as in Figure 4, the inflection point was obtained, and it was found to be 4.5 (inflection point = pKa). As a result, the experimental value of this pKa was almost equal to the theoretical pKa of bromocresol green that is 4.7. The percentage error can therefore be calculated as: % error = experimentalvalue – actualvalue / actualvalue x 100% = 4.5 – 4.7/4.5 x 100% = 4.4%
The experiment had an experimental error of 4.4% which is small, thus acceptable.
On the other hand, the second method utilized the Henderson-Hasselbach equation and the Beer’s Additive Law to determine the linear relationship between pH and concentration of solutions. For the second, method, the pKa was calculated at 4.46 and this is almost equal to that of the first method.
The difference in the experimental and theoretical pKa values suggest the occurrence of experimental errors. These might be due to stray radiation or errors in measuring the volume of solutions, which interfered with the absorbance values and ionic strength of the various solutions, respectively. As a result, this had a consequent effect on the overall findings.
Aside from the UV-VIS Spectrophotometry, the experiment can also be conducted using Agilent Technologies Carry 8454 UV-Vis that provides more accurate results (2).
human
Swap the first and the last sentence.
assistant
Aside from the UV-VIS Spectrophotometry, the experiment can also be conducted using Agilent Technologies Carry 8454 UV-Vis that provides more accurate results (2).65][0.0458]/0.09 = 0.33
pKa = 5.322 – log [0.65]/[0.09] = 4.46
The pKa value is essential and unique to every indicator. In this experiment, two methods were employed to determine pKa. The first method revolved around measuring the pH of the buffer solutions and determination of the absorbance. From the results, as in Figure 4, the inflection point was obtained, and it was found to be 4.5 (inflection point = pKa). As a result, the experimental value of this pKa was almost equal to the theoretical pKa of bromocresol green that is 4.7. The percentage error can therefore be calculated as: % error = experimentalvalue – actualvalue / actualvalue x 100% = 4.5 – 4.7/4.5 x 100% = 4.4%
The experiment had an experimental error of 4.4% which is small, thus acceptable.
On the other hand, the second method utilized the Henderson-Hasselbach equation and the Beer’s Additive Law to determine the linear relationship between pH and concentration of solutions. For the second, method, the pKa was calculated at 4.46 and this is almost equal to that of the first method.
The difference in the experimental and theoretical pKa values suggest the occurrence of experimental errors. These might be due to stray radiation or errors in measuring the volume of solutions, which interfered with the absorbance values and ionic strength of the various solutions, respectively. As a result, this had a consequent effect on the overall findings. Ka = [0.
human
How about a  * Equation 1: section.
assistant
Hln (aq) + H 2 O ⇔ H 3 O + (aq) + ln – (aq)
 * Quantitatively, the relationship between the hydronium concentration, H 3 O + , and the relative amounts of Hln and ln – in solution is described by the acid-dissociation constant, K a. Based on the equation above, the acid strength is calculated as:
   +
human
Give me  * Equation 6: section.
assistant
+ 0.0484 = ε x 1 [0.95]
   + ε=0.05
human
Give me #Figure 2. Graph of Absorbance at 444nm of the second derivative where pH is in the X-axis and Absorbance in the Y-axis. section.
assistant
Moreover, the values from the data table in Appendix 2, were used to plott Figures 3 and 4 for the absorbance at the 619nm wavelength.
human
Give me    + [Hln] = 0.09 section.
assistant
human
Give me #Table 1: Absorbance values at 444nm, 508nm and 619nm wavelengths as a function of pH. section.
assistant
Buffer pH   AU, 444nm AU, 508nm AU, 619nm
1    2.597 0.251   0.101   0.0152  
2    3.02  0.2848   0.1123   0.0281  
3    4.054 0.2359   0.1115   0.1628  
4    4.853 0.152   0.1063   0.3797  
5    5.322 0.1153   0.1075   0.5003  
6    6.196 0.0513   0.1083   0.6566  
7    7.102 0.0448   0.1046   0.6699  
8    7.856 0.0484   0.1111   0.6884  
Using values from the data table in Appendix 2, the Figures 1 and 2 were plotted for the absorbance at the 444nm wavelength.
human
Give me  * Equation 7: section.
assistant
+ 0.6884 = ε x 1 [0.95]
   + ε=0.73
To determine, the pKa of the indicator, calculation using values for Buffer 5 were used as it has an intermediate pH.
human
Put it all togegther in the right order.
assistant
#Spectrophotometric Determination of the pKa of an Acid-Base Indicator Report
##Introduction
Acid-base indicators are used to show the end-points of acid-base reactions. Most acid-base indicators, including bromocresol green, are regarded as weak acids. The indicator is a complex molecule that can be represented with the formula Hln, where ln- represents the anion. When applied to low concentrations, the indicators signal pH changes within a particular range, which is variable among the indicators. The color change depends on the relative acid strength (pKa) of the conjugate acid form of the indicator. The formula below shows how weak acids ionize in aqueous solutions:
## * Equation 1:
   + Hln (aq) + H 2 O ⇔ H 3 O + (aq) + ln – (aq)
 * Quantitatively, the relationship between the hydronium concentration, H 3 O + , and the relative amounts of Hln and ln – in solution is described by the acid-dissociation constant, K a. Based on the equation above, the acid strength is calculated as:
   + 
## * Equation 2
   + Equation 2 can also be represented as:
   + 
## * Equation 3
   + The ratio of the indicator concentration is controlled by the pH of the solution, while the solution pH controls the ratio of the buffer concentration. The pH of a solution is measured using a pH meter.
Aside from using a pH meter, Ka can also be determined spectrophotometrically by employing Beer Lambert’s law. According to the law, for substances to absorb light within the visible region of the electromagnetic spectrum, the absorbance or the amount of light absorbed is directly proportional to the molar concentration (1). Consequentially, the absorption curve of an indicator at various pH levels can be examined to determine the Ka of the indicator. This experiment aims to determine the pKa of an acid-base indicator, Bromocresol Green, using spectrophotometery.
Wenzel, T. (2018). Beer’s Law.
##Experimental
##Reagents
 * Disodium Phosphate Solution, Na 2 HPO 4, 0.20 M
 * Citric Acid, C₆H₈O₇, 0.10 M
 * Bromocresol Green Indicator, C 21 H 14 Br 4 O 5 S.
##Solutions
 * Disodium Phosphate Solution, 0.20 M. Dissolve the calculated amount of anhydrous disodium phosphate, Na 2 HPO 4 , or disodium hydrogen phosphate heptahydrate, Na 2 HPO 4 ·7H 2 O, in about 200 mL of distilled water and dilute to the mark in a 250 mL volumetric flask.
 * Citric Acid, 0.10 M. Dissolve the calculated amount of citric acid monohydrate about 200 mL of distilled water and dilute to the mark in a 250 mL volumetric flask.
 * Bromocresol Green Indicator. Crush and mix 0.1000 g (exact mass is needed in order to calculate the concentration) of bromocresol green indicator with 14.3 mL of 0.010 M NaOH in a mortar. Transfer to a 250 mL volumetric flask and dilute to volume with distilled water.
 * Buffer 1. Add 9.50mL of stock 0.1M citric acid solution to 0.50mL of stock 0.20M disodium phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 2. Add 8.00mL of stock 0.1M citric acid solution to 2.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 3. Add 6.00mL of stock 0.1M citric acid solution to 4.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 4. Add 5.50mL of stock 0.1M citric acid solution to 4.50mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 5. Add 5.00mL of stock 0.1M citric acid solution to 5.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 6. Add 4.00mL of stock 0.1M citric acid solution to 6.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 7. Add 2.00mL of stock 0.1M citric acid solution to 8.00mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
 * Buffer 8. Add 0.50mL of stock 0.1M citric acid solution to 9.50mL of stock 0.20M phosphate solution. Dilute with distilled water to the mark in a 50mL volumetric flask.
##Instrumentation
 * ThermoFisher Evolution Array Spectrophotometer
 * pH meter
##Procedure
The procedure listed in the Instrumental Methods of Analysis Chem 447 of the Winter 2021 laboratory manual was followed.
Eight buffer solutions were prepared from varied concentrations of the phosphate and citric acid solutions. The pH of the buffer solutions was then measured distinctly using a pH meter and recorded. Bromocresol Green indicator solution was then added to each buffer and then cuvettes containing the solutions placed in the spectrophotometer to measure their absorbance wavelength.
##Results and Discussion
Absorbance measurements were performed using a Thermo Scientific Evolution Array Spectrophotometer in the wavelength range between 400 and 800 nm. Plots of absorbance against λ for the bromocresol green indicator in buffers with different pH levels are illustrated in Figures 1, 2, 3 and 4.
###Table 1: Absorbance values at 444nm, 508nm and 619nm wavelengths as a function of pH.
Buffer pH   AU, 444nm AU, 508nm AU, 619nm
1    2.597 0.251   0.101   0.0152  
2    3.02  0.2848   0.1123   0.0281  
3    4.054 0.2359   0.1115   0.1628  
4    4.853 0.152   0.1063   0.3797  
5    5.322 0.1153   0.1075   0.5003  
6    6.196 0.0513   0.1083   0.6566  
7    7.102 0.0448   0.1046   0.6699  
8    7.856 0.0484   0.1111   0.6884  
Using values from the data table in Appendix 2, the Figures 1 and 2 were plotted for the absorbance at the 444nm wavelength.
###Figure 1. Graph of Absorbance at 444nm of the first derivative where pH is in the X-axis and Absorbance in the Y-axis.
###Figure 2. Graph of Absorbance at 444nm of the second derivative where pH is in the X-axis and Absorbance in the Y-axis.
Moreover, the values from the data table in Appendix 2, were used to plott Figures 3 and 4 for the absorbance at the 619nm wavelength.
###Figure 3. Graph of Absorbance at 619nm of the second derivative where pH is in the X-axis and Absorbance in the Y-axis.
###Figure 4. Graph of Absorbance at 619nm of the second derivative where pH is in the X-axis and Absorbance in the Y-axis.
Based on Figure 4, the inflection point is at the pH” of 4.5. At this point, pH” = pKa, hence the pKa, is also 4.5.
Buffer 1 is the most acidic. The molar absorptivity at Hln is:
## * Equation 4:
   + 
   + 0.25 =ε x 1 [0.95]
   + ε=0.26
##   + Equation 5:
   + 
   + 0.0152 = ε x 1 [0.95]
   + ε=0.016
Buffer 8 is the most basic. The molar absorptivity at Hln is:
## * Equation 6:
   + 
   + 0.0484 = ε x 1 [0.95]
   + ε=0.05
## * Equation 7:
   + 
   + 0.6884 = ε x 1 [0.95]
   + ε=0.73
To determine, the pKa of the indicator, calculation using values for Buffer 5 were used as it has an intermediate pH.
## * Equation 8:
   + 
   + 0.1153 = 0.73 (0.1 – [Hln]) + 0.26 x 1[Hln]
   + 0.1153 = 0.073 – 0.73 Hln + 0.26Hln
##   + 0.0423 = 0.47Hln
##   + [Hln] = 0.09
## * Equation 9:
   + 
   + 0.5003 = 0.73[ln-] + 0.26 × 0.09
   + 0.5003 – 0.0234 = 0.73[ln-]
##   + [ln-] = 0.65
Ka = [0.65][0.0458]/0.09 = 0.33
pKa = 5.322 – log [0.65]/[0.09] = 4.46
The pKa value is essential and unique to every indicator. In this experiment, two methods were employed to determine pKa. The first method revolved around measuring the pH of the buffer solutions and determination of the absorbance. From the results, as in Figure 4, the inflection point was obtained, and it was found to be 4.5 (inflection point = pKa). As a result, the experimental value of this pKa was almost equal to the theoretical pKa of bromocresol green that is 4.7. The percentage error can therefore be calculated as: % error = experimentalvalue – actualvalue / actualvalue x 100% = 4.5 – 4.7/4.5 x 100% = 4.4%
The experiment had an experimental error of 4.4% which is small, thus acceptable.
On the other hand, the second method utilized the Henderson-Hasselbach equation and the Beer’s Additive Law to determine the linear relationship between pH and concentration of solutions. For the second, method, the pKa was calculated at 4.46 and this is almost equal to that of the first method.
The difference in the experimental and theoretical pKa values suggest the occurrence of experimental errors. These might be due to stray radiation or errors in measuring the volume of solutions, which interfered with the absorbance values and ionic strength of the various solutions, respectively. As a result, this had a consequent effect on the overall findings.
Aside from the UV-VIS Spectrophotometry, the experiment can also be conducted using Agilent Technologies Carry 8454 UV-Vis that provides more accurate results (2).
##Summary
The application of spectrophotometric titration allowed the pKa of Bromocresol Green to be determined. Two methods of analysis (graphical and additivity of Beer’s Law) were employed and generated results with good similarity. The isosbestic point was also determined. In comparison, the first method proved to be more accurate than the second.