Bromthymol blue indicators

Add to the filtrate three drops of methyl orange or bromthymol blue indicator. Note if acid color appears... 

Serum cholinesterase with bromthymol blue indicator and acetylcholine as a substrate detects the cholinesterase-inhibiting insecticides (36). 

You just learned that a salt is an ionic compound made up of a cation from a base and an anion from an acid. What reaction, if any, occurs when a salt is dissolved in pure water In Figure 19-21, several drops of bromthymol blue indicator solution have been added to O.IOM aqueous solutions of the salts ammonium chloride (NH4CI), sodium nitrate (NaN03), and potassium fluoride (KF). Sodium nitrate turns the indicator green, which means that a solution of sodium nitrate is neutral. However, the blue color of the KF solution means that a solution of potassium fluoride is basic, and the yellow color of the ammonium chloride solution indicates that the NH4CI solution is acidic. Why are some aqueous salt solutions neutral, some basic, and some acidic ... 

Bromthymol blue indicator is yellow in acidic solutions and blue in basic solutions. 

Figure 21-4 The electrolysis of aqueous Na2S04 produces H2(g) at the cathode and O2 at the anode. Bromthymol blue indicator has been added to the solution. This indicator turns blue in the basic solution near the cathode (where OH is produced) and yellow in the acidic solution near the anode (where H+ is formed).

A FIGURE 7.17 The reaction of CO2 with water containing a bromthymol blue indicator. Initially, the blue color tells us the water is slightly basic. When a piece of solid carbon dioxide ( dry ice ) is added, the color changes to yellow, indicating an acidic solution. The mist is water droplets condensed from the air by the cold CO2 gas. 

Bromthymol blue indicator solution — Dissolve one g of reagent grade indicator in 500 ml of distilled water made alkaline with one pellet of sodium hydroxide. 

A stirring bar is added to the cooled solution and rapid stirring initiated over a magnetic stirring motor. Approximately 130 ml of concentrated ammoniiun hydroxide are added cautiously, followed by 1 ml of bromthymol blue indicator solution. Neutralization is completed by addition of concentrated ammonium hydroxide to the yellow-green endpoint. If necessary, the sample volume is readjusted to its original value with distilled water. Concentrated nitric acid is added to make the solution 0.15 M in HNOg (Table VIII-l). 500 mg of hydroxylamine hydrochloride are added to the solution and the beaker placed in a steam bath heated to 80 5 C. Concentrated phosphoric acid is then added to a concentration of approximately 0.09 M (Table Vin-1). An amount of bismuth nitrate solution, equivalent to 60 mg bismuth per 100 ml, is added dropwise to the heated, stirred solution. 

HjCfOHjSOs (aq).Asthe hydrogen sulfite ion is used up, the solution becomes less acidic, then changes to basic. Bromthymol-blue indicator marks the change from acidic to basic by changing from yellow to blue. 

Left Calcium hydroxide solution with bromthymol-blue indicator. Center Carbon dioxide from dry ice reacts with calcium ion to precipitate calcium carbonate. Right In an excess of carbon dioxide,the calcium carbonate dissolves to form a solution of calcium ion and hydrogen carbonate ion, HCOs". In this acidic solution, bromthymol blue changes to a yellow color. 

The flask contains hydrogen chloride gas.When water is added to the flask from the dropper, the hydrogen chloride dissolves in it, reducing the pressure in the flask. Atmospheric pressure pushes the water in the beaker into the flask, forming a stream or fountain.Water in the beaker has bromthymol-blue indicator in it.The indicator solution in the flask is yellow because it is acidic. 

Each of these 1 M solutions contains bromthymol blue indicator, which has the following colors ... 

The yellow color of bromthymol blue indicator in Al2(S04)3(aq) denotes that the solution is acidic. The pH meter gives a more precise indication of the pH. 

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. 

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 ... 

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. 

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.)... 

PROBLEM 16.17 The following acid-base indicators change color in the indicated pH ranges bromthymol blue (6.0—7.6), thymolphthalein (9.4-10.6), and alizarin yellow (10.1-12.0). Which indicator is best for the titration in Problem 16.16 Which indicator is unacceptable Explain. 

Thiocyanates are obtained by fusing alkali cyanides with sulfur the reaction of S with KCN is rapid and quantitative, and S in benzene or acetone can be titrated with KCN in 2-propanol with bromthymol blue as indicator. Thiocyanate is the product of detoxification of CN" in living systems. 

Bromthymol blue, an indicator with a Ka value of 1.0 X 10-7, is yellow in its HIn form and blue in its In- form. Suppose we put a few drops of this indicator in a strongly acidic solution. If the solution is then titrated with NaOH, at what pH will the indicator color change first be visible ... 

Bromthymol blue is a good indicator choice since it changes color at pH 7 (from base color to acid color). 105. Since the equivalence point occurs at pH = 8.9, phenolphthalein would be a good indicator choice because it changes color at pH 9 (from acid color to base color). 107. a. 6.7 x 10-6 M-, b. 1.2 x 10 13 M c. No, since Q (= 2.3 x 10—21) is less than the Ksp value. 

Indicator Bromphenol blue Methyl orange Methyl red Bromcresol purple Bromthymol blue Phenol red Cresol red Thymol blue Phenolphthalein Thymolphthalein... 

We see that to obtain the most accurate results in titrating a strong acid and a strong base an indicator with indicator constant about 10 pK = 7) should be chosen, such as litmus or bromthymol blue. The titration curve calculated above, and given in Figure 20-3, shows however that the choice of an indicator is in this case not crucial any indicator with pK between 4 (methyl orange) and 10 (thymolphthalein) could be used with error less than 0.2%. 

All indicators have a transition range. In this range, the indicator is partly in its acidic form and partly in its basic form. Thus, the indicator s color is intermediate between those of its acid and base colors. Figure 19 illustrates the transition range for two typical indicators, bromthymol blue and phenolphthalein. 

In titrations of a strong acid by a strong base, the equivalence point occurs at pH 7, and bromthymol blue would be an appropriate indicator, as Table 6 confirms. However, when a weak acid is titrated by a strong base, the equivalence point is at a pH greater than 7 and thymol blue or phenolphthalein would be a better choice. On the other hand, methyl orange could be the best choice if your titration uses a weak base and a strong acid, because the equivalence point might be at pH 4. 

The indicator bromthymol blue provides surprising results when added to three solutions of ionic salts. An ammonium chloride solution is acidic, a sodium nitrate solution is neutral, and a potassium fluoride solution is basic. The explanation has to do with the strengths of the acid and base from which each salt was formed. 

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