Bromthymol Blue

Ramsing and colleagues developed an FfA method for acid-base titrations using a carrier stream mixture of 2.0 X f0 M NaOH and the acid-base indicator bromthymol blue. Standard solutions of HCl were injected, and the following values of Af were measured from the resulting fiagrams. 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

Table 14.2 shows die characteristics of three indicators methyl red, bromthymol blue, and phenolphthalein. These indicators change colors at pH 5,7, and 9, respectively. 

In practice it is usually possible to detect an indicator color change over a range of about two pH units. Consider, for example, what happens with bromthymol blue as the pH... 

A weak acid-strong base titration. The curve represents the titration of 50.00 mL of 1.000 M acetic acid, HC2H3O2. with 1.000 /W NaOH. The solution at the equivalence point is basic (pH = 9.22). Phenolphthalein is a suitable indicator. Methyl red would change color much too early, when only about 33 mL of NaOH had been added. Bromthymol blue would change color slightly too quickly. 

From Figure 14.5 and Example 14.7, we conclude that any indicator that changes ccdor between pH 4 and 10 should be satisfactory for a strong acid-strong base titration. Bromthymol blue (BB end point pH = 7) would work very well, but so would methyl red (MR end point pH = 5) or phenolphthalein (PP end point pH = 9). 

Given three add-base indicators—methyl orange (end point at pH 4), bromthymol blue (end point at pH 7), and phendphthalein (end point at pH 9)—which would you select for the following acid-base titrations ... 

Free alkali Bromthymol blue titration Alkali-acid neutralization... 

Although litmus paper, cabbage juice, and phenolphthalein can indicate whether a substance is acidic or basic, they have limitations in that they cannot determine an exact pH. To do this, an acid-base indicator called universal indicator can be used. Universal indicator is actually a mixture of several different acid-base indicators (usually phenolphthalein, methyl red, bromthymol blue, and thymol blue). This mixture produces a wide range of colors to indicate different pHs. Under very acidic conditions, universal indicator is red. It turns orange and then yellow between the pHs of 3 to 6. It is green at neutral pH and turns greenish-blue as a solution becomes more alkaline. In very basic conditions, universal indicator turns a dark purple color. 

When a solution is colorless with phenolphthalein, pH < 8. When a solution is blue in bromthymol blue, pH > 7.6. When a solution is yellow in methyl orange, pH > 4.4. Therefore, we know that this solution has a pH between 7.6 and 8. 

Using Appendix B, you would choose bromthymol blue (range 6.0 to 7.6, Lower color-yellow Upper color-blue) and m-Cresol purple (range 7.5 to 9.0, Lower color-yellow Upper color-violet) because bromthymol blue s high-end color (blue) ends where m-cresol purple s low-end color (yellow) begins. The pH would be between 7.5-8.5. 

Methyl violet Cresol red Thymol blue Methyl orange Bromcresol green Methyl red Bromthymol blue Phenolphthalein Thymolphthalein Clayton yellow... 

Bromthymol Blue 4,4 -(3H-2,l-Benzoxathiol-3-ylidene)bis[2-bromo-3-methyl-6-(1-methylethyl) phenol]S,S-dioxide... 

O ttflif If you were titrating a strong base with a weak acid, which of these indicators might be suitable bromphenol blue, bromthymol blue, or phenolphthalein (Refer to Figure 9.3.)... 

The dye bromthymol blue will react with haemoglobin at a large number of sites. If haem-haem interaction is functioning the reaction occurs several times faster w ith reduced haemoglobin than with oxyhaemoglobin. If haem-haem interaction is destroyed by digestion with carboxypeptidase A this difference disappears. In the case of the carboxy-... 

Dissolve 60 mg methyl yellow, 40 mg methyl red, 80 mg bromthymol blue, 100 mg thymol blue and 20 mg phenolphthalein in 100 ml of ethanol and add enough 0.1 AT NaOH to produce a yellow color. 

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