Bromothymol blue, acid-base

A 15.0-mL sample of a solution of H2SO4 with an unknown molarity is titrated with 32.4 ml of 0.145MNaOH to the bromothymol blue endpoint. Based upon this titration, what is the molarity of the sulfuric acid solution ... 

Standardization—External standards, standard additions, and internal standards are a common feature of many quantitative analyses. Suggested experiments using these standardization methods are found in later chapters. A good project experiment for introducing external standardization, standard additions, and the importance of the sample s matrix is to explore the effect of pH on the quantitative analysis of an acid-base indicator. Using bromothymol blue as an example, external standards can be prepared in a pH 9 buffer and used to analyze samples buffered to different pHs in the range of 6-10. Results can be compared with those obtained using a standard addition. 

A related assay was later reported which makes use of a different and more convenient indicator (bromothymol blue) 78). However, it is emphasized that all of the assays based on pH change reported so far refer to the use of isolated enzymes. In real applications, supernatants are likely to be used, as in directed evolution studies. In supernatants, however, pH variations may occur. Therefore, an optimized assay was later developed in which supernatants are employed (79). Thus, the pH of the buffer is adjusted to the acidity of the medium, enabling about 4000 samples in kinetic resolution investigations to be screened per day. 

The sensing microzone of the flow-through sensor depicted in Fig. 5.9.B1 integrates gas-diffusion and detection with two analytical reactions [28], viz. (a) the urease-catalysed formation of ammonium ion by hydrolysis of urea (the analyte), which takes places on a hydrophilic enzyme membrane in contact with the sample-donor stream, which contains a gel where the enzyme is covalently bound and (b) an acid-b reaction that takes place at the microzone on the other side of the diffusion membrane and involves Bromothymol Blue as indicator. This is a sandwich-type sensor including a hydrophilic and a hydrophobic membrane across which the sample stream is circulated —whence it is formally similar to some enzyme electrodes. Since the enzymatic conversion of the analyte must be as efficient as possible, deteetion (based on fibre optics) is performed after the donor and acceptor streams have passed through the sensor. Unlike the previous sensor (Fig. 5.9.A), this does not rely on the wall-jet approach in addition, each stream has its own outlet and the system includes two sensing microzones... 

Finally, acids and bases can change the colors of certain indicators. Some examples are phenolphthalein and litmus. The chart below summarizes the colors of these two important indicators. A good mnemonic device to help you remember litmus indicators is BRA Blue turns Red in Acid. Other indicators that can be used are methyl orange and bromothymol blue. 

Bromothymol blue and cabbage juice work in much the same way as phenolphthalein. As the acidity of the solution they re in changes, their molecular structure changes as well. These different structures, three kinds in each case, re-radiate different colors of light. Of course, there are many more kinds of acid-base indicators, and each one is either a weak, low-concentration acid or a weak, low-concentration base. That s why they interact with the acids and bases... 

Figures 14-5 and 14-6 show that the choice of indicator is more limited for the titration of a weak acid than for the titration of a strong acid. For example. Figure 14-5 illustrates that bromocresol green is totally unsuited for titration of 0.1000 M acetic acid. Bromothymol blue does not work either because its full color change occurs over a range of titrant volume from about 47 mL to 50 mL of 0.1000 M base. An indicator exhibiting a color change in the basic region, such as phenolphthalein, however, should provide a sharp end point with a minimal titration error.

Strong acid and strong base NaOH v/s HCl, NaOH v/s H2SO4 KOH v/s HCl etc. Methyl orange, methyl red, Bromothymol blue, Phenolphthalein 5 to 10... 

The indicators were obtained from Kodak Laboratory Chemicals, Aldrich Chemical Company, and J.T. Baker and were used without further purification. The indicators employed in the majority of the titrations were bromocresol green and bromothymol blue each of which exhibits two acid-base transitions at Pka = -3.7, +4.6, and -1.5, +6.8, respectively(20, 22, 26) The medium for the titration and electrophoretic mobility experiments was benzene (Burdick and Jackson Laboratories) having a water content of less than 0.03 percent. The base used as titrant was n-butylamine, Baker analyzed reagent grade. 

Hydrobromic acid and potassium hydroxide are referred to as the parent acid and the parent base of potassium bromide. Test several aqueous salt solutions with bromothymol blue indicator to determine whether the solutions are acidic (yellow), basic (blue), or neutral (green). 

This method has been extensively exploited for the synthesis of a large group of 3H-2,1-benzoxathiole 1,1-dioxide derivatives known as sulphonephthaleins, many of which, such as phenol red, p-cresol red and bromothymol blue are well known acid-base indicators. There is excellent coverage of this subject in Breslow and Skolnik s monograph8 and equation 60 merely serves to illustrate two representative syntheses81,82. The sulphonephthaleins can also be prepared from 3ff-2,l-benzoxathiole-l-dioxide derivatives with reactive substituents (such as dichloro or carbonyl) at the 3-position (see Section III.D.3). 

The manifold used for acido-basic titrations of strong acid with strong base using bromothymol blue as indicator added directly to the alkaline carrier solution is shown in Fig. 4.60a, while the recorder output is shown in Fig. 4.60 7. Here, all the five titration cycles made are recorded from the same starting point (5), showing the practical consequences of performing titrations at medium D values. First, the titration cycle, including the washout period, can be made as short as 12 s with an equivalence A/ of 2.2 s hence, it is necessary to acquire the readouts by means of a... 

Exercise The quantitative determination of the acid concentration is based on titration of the acid (HCl) with base (NaOH), the acid samples being injected into a FIA system comprising a mixing chamber (Fig. 6Ja) in which a controlled dilution gradient of the samples can be created (cf. Sections 2.4.4 and 4.9). As carrier stream is used a 1.0 x 10 M NaOH solution containing the indicator bromothymol blue. 

Mixed acid-base indicator 0.02 g cresoi red, 0.04 g bromothymol blue, and 0.08 g bromocresol purple dissolved in 3 ml 0.1 M NaOH, and diluted to 100 ml with... 

The acid reaction occurs, as defined in the test, when methyl red changes from yellow to orange or red at about 5.1 pH or when bromothymol blue changes from blue to yellow at about 7.1 pH. This means that most tertiary and quaternary amines are found in the ionic acid form, and this allows the thereby cationic alkaloid to precipitate with anionic iodobismuthate. The salt is believed to be constituted not of monomeric entities, of for example one nitrogen base and one iodobismuthate, but of oligomeric cations and anions. 

Paper chromatography is extensively used to follow the progress of the malolactic fermentation and the simplicity of this method is such that practically all wineries can carry it out. It is based on the difference in R values between malic and lactic acids using a mobile phase consisting of acetic acid and butanol. Bromothymol blue is incorporated into the mobile phase as indicator and thus the acids appear as yellow spots on a blue background. The absence of a spot for malic or lactic acid indicates that the MLF has or has not, respectively, taken place. 

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