Your online site for school work help and homework help. This occurs when [In–]=[HIn]. Assign one person to be the timer, and one person to perform the experiment. With these values, we can plot a graph of pH vs. log([In–]/[HIn]) (figure 4). Experiment 2 Part 1 - lab report Experiment 6 - lab report Experimnet 7 - lab report Lab 8 back lab - lab report Experiment 6 - lab report Experiment 8 - lab report Preview text EXPERIMENT 11 - DETERMINATION OF THE pKa OF BROMOTHYMOL BLUE In this experiment, spectrophotometry is used to determine the pKa of bromothymol blue, a monoprotic acid-base indicator (HIn). 1 Product Result | Match Criteria: Description Empirical Formula (Hill Notation): C 27 H 27 Br 2 NaO 5 S. Molecular Weight: 646.36. Figure 3 is a graph of absorbance vs. pH. ATTENTION: Please help us feed and educate children by uploading your old homework! We measured the absorbance at this pH because it was within the transitional range of bromothymol blue. Add enough bromothymol blue for the water to be visibly blue. By graphing pH vs. log(([In–]/[HIn]) (values in table 2), one gains a line with slope approximately of 1 and a y-intercept of the pKa value. This would prevent inaccuracies in the time it takes to change to acidic. What would its color be at a pH of 7.0? The pH range for the indicator is 7.6 (blue) to 6.0 (yellow), with green appearing around pH 7. 7.1) that is used as a biological slide vital stain to define cell walls or nuclei under the microscope. It is also important to note the isobestic point that occurs approximately at 496.9 nm with an absorbance of 0.049. First we added 1 mL of 0.1 M HCl to 15 mL of water. The secret to this experiment is a pH indicator called bromothymol blue. From Figure 2, a graph of all of the absorbance spectra superimposed on each other, as well as Table 1, it is possible to calculate the ratio [In–]/[HIn]. The two absorbance values from these graphs, 0.106 at 435.5 nm and 0.287 at 614.5 nm, along with the other absorbance values from the intermediate pH trials are used to calculate the ratio [In–]/[HIn]. 2. bromothymol blue solution (100 mL) 400 mL beakers (2) graduated cylinder. 3. In an alkaline solution (7.6) it is blue; in an acid solution it is yellow. Bromothymol Blue is a liquid indicator that can detect presence CO2 in water. As seen in Graph 1 there is not much data because the averages of all of the trials were taken which was only four points and they had weak correlation, so a trend cannot really be produced. Respiration. Bromothymol Blue (BTB) is a pH indicator (pKa approx. One example of a demonstration used across most science disciplines and grade levels involves bromothymol blue (BTB). Figure 4 is a graph of the Henderson-Hasselbalch equation, pH=pKa+log([In–]/[HIn]). As they blow (it will take 3-4 big breaths) the water will slowly change from blue to yellow. If the total concentration of bromothymol blue were not fixed, the reference absorbance values will not work in calculation and the ratio [In-]/[HIn] will not be calculated properly for all trials. L.A. Shelef, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003. These wavelength values did not deviate much from the values in the literature and although the calculated pKa varied slightly with the value from the online literature, the value in the literature is an approximation. BROMOTHYMOL BLUE EXPERIMENT: 1. Determining the pKa of Bromothymol Blue by spectrophotometry. acid indicator with colors that ranged from acidic yellow to neutral green, then basic blue. Depending on the interests or abilities of O2 (released during photosynthesis) in solution. As vaginal pH normally is acidic, the blue color indicates the presence of amniotic fluid. At each lab station you will find 2 beakers. It is important to keep the total concentration of bromothymol blue constant so that [In-]+[HIn] always equals the same total concentration. To determine the pKa of an acid-base indicator, specifically bromothymol blue, different amounts of both 0.1M NaOH and 0.1 M HCl were added to a solution of fixed concentration of bromothymol blue and the pH was monitored via pH meter. This along with the fact that resting heart rate was reached before each trial ensured that everything started at the same point. The times for each increment were recorded, averaged, and graphed on a scatter plot to depict the trend. The predicted outcome was that the time to turn to acid would decrease as exercise duration went up, This is supported by the fact that higher exercise rates mean increased respiration which produces more CO2 that changes a base to an acid. Three people performed the exercise of running stairs for increments of one two and three minutes, so respiration could be reached. Another question that could be researched is whether different types of exercise cause more respiration compared to others with variables of activity and time it takes a basic solution to become acidic. It is important to have a control for this experiment because it allows the experiment to minimize the changes in all other variables except the one being tested, proving that it is causing the reaction. In a test tube, you will see that: bromothymol blue + CO2 = green color. Students will record their data which will be used to conclude whether carbon dioxide was consumed or released by the elodea. Amniotic fluid typically has a pH > 7.2, bromothymol will therefore turn blue when brought in contact with fluid leaking from the amnion. These measurements from the diluted HCl and NaOH solutions provide us with an absorbance that is almost 100% HIn and another that is almost 100% In-, respectively. Often science teachers perform demonstrations only to discover that students have already seen the experiment in a previous course. It changes color from blue to green, as it detects the presence of the CO2 . Although you will not carry out the experiment, you will receive … This process was repeated twice more to gain two absorbance spectra, one of pH 5.5 and another of pH 8.1. Bromothymol blue agar. Experiment - The Elements of Photosynthesis Worksheet 1. I want to use bromothymol blue, a pH indicator, to measure the amount of carbon dioxide a person exhales, but don't know how to properly use it. Acid solution it is yellow breaths ) the water will slowly change from blue to green, then blue... Food Sciences and Nutrition ( Second Edition ), with green appearing around pH 7 to... To green or yellow Nutrition ( Second Edition ), 2003 calculations, I will call max... Solution until you see the color with your breath blue ) of bromothymol blue was drop-wise. 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