Indicators mixed acid-base

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... 

Bassam Z. Shakhashiri, "Rainbow Colors with Mixed Acid-Base Indicators," Chemical Demonstrations A Handbook for Teachers of Chemistry, Vol. 3 (The University of Wisconsin Press, Madison, 1989) pp. 41-46. 

The acidity of various substances is determined with a pH meter or acid—base indicators. This may also be done by mixing or diluting solutions. (See the Equilibrium chapter.)... 

In an acid-base titration, you carefully measure the volumes of acid and base that react. Then, knowing the concentration of either the acid or the base, and the stoichiometric relationship between them, you calculate the concentration of the other reactant. The equivalence point in the titration occurs when just enough acid and base have been mixed for a complete reaction to occur, with no excess of either reactant. As you learned in Chapter 8, you can find the equivalence point from a graph that shows pH versus volume of one solution added to the other solution. To determine the equivalence point experimentally, you need to measure the pH. Because pH meters are expensive, and the glass electrodes are fragile, titrations are often performed using an acid-base indicator. 

The last of these methods has been applied particularly to chemical reaction vessels. It is covered in detail in Chapter 17. In most cases, however, the RTDs have not been correlated with impeller characteristics or other mixing parameters. Largely this also is true of most mixing investigations, but Figure 10.3 is an uncommon example of correlation of blend time in terms of Reynolds number for the popular pitched blade turbine impeller. As expected, the blend time levels off beyond a certain mixing intensity, in this case beyond Reynolds numbers of 30,000 or so. The acid-base indicator technique was used. Other details of the test work and the scatter of the data are not revealed in the published information. Another practical solution of the problem is typified by Table 10.1 which relates blend time to power input to... 

Colors of adsorbed Hammett indicators can be used to bracket the H0 of a solid surface in the same way that the colors of more conventional acid-base indicators are used to bracket the pH of an aqueous solution. Thus, when an acid color is observed for the adsorbed indicator, the H of the solid surface is equal to or lower than the pKa of the indicator. As an example, a solid surface that has an H0 that lies between + 1.5 and -3.0 gives an acid color with benzeneazodiphenylamine (with a pKa of + 1.5) and a basic color with dicinnamalacetone (pKa of - 3.0). Color tests are made by adding 3-5 ml of dry solvent (e.g., benzene) to roughly 0.1 g of dried, powdered solid in a test tube, adding a few drops of a 0.1% solution of indicator in benzene, mixing the resulting suspension, and noting the color formed on the powdered solid. 

Adds and bases cause certain colored dyes to change color. The most common of these dyes is litmus. When mixed with an acid, litmus is red. When added to a base, litmus is blue. Therefore, litmus is a reliable indicator of whether a substance is an acid or a base. Figure 14.2 shows how vegetable dyes change color in the presence of an acid or a base. Dyes such as these are called acid-base indicators because they are often used to indicate whether substances are acids or bases. 

Ammonium Industrial effluents Pervaporation UV-Vis 0.1 mg L-1 Flow injection system mixed cresol red/thymol blue acid—base indicator solution as the acceptor stream results unaffected by surfactants, other organics and suspended solids [273]... 

Some typical mixing-time data obtained by Norwood and Metzner for turbine impellers in baffled vessels using an acid/base/indicator technique are presented in Figure 8.10. Much of the mixing-time data presented in the literature is concerned with blending liquids of equal density and viscosity. However, these studies will often underestimate the blend times required for components of unequal density and/or viscosity. ... 

Tucker SA, Bates HC, and Acree WE (1995) Acid-base indicators — transition colors and pH ranges determined in select aqueous-organic mixed-solvents. Analyst 120 2277-2279. 

The reactant tertiary butyl chloride, f-BuCI, in aqueous solvent exchanges the Cl group w/ith an HO to give tertiary butanol, f-BuOH, as the product. The reaction rate is determined by the rate of formation of carbocation intermediate, f-Bu" and is first order in f-BuCI. The disappearance of the reactant can be monitored by electrical conductance, the speed at w/hich ions formed in the reaction travel through solution, or, approximately, by using an acid-base indicator. The reaction starts by mixing f-BuCI with solvent to make a 0.020 M concentration at f = 23°C. After 45 s the concentration of f-BuCI is 8.13x10" M and after 2 min 15 s, it is down to 1.31 xl0 M. (A) Use these data to calculate the reaction rate,/c[s ], of the hydrolysis of f-BuCI to f-BuOH.(B) How much time [s] would it take for the reactant to drop to 1/2 of the initial concentration ... 

In some clock reactions, however, there is a narrow range of concentrations in which the quality of the mixing becomes critically important. Under these conditions, the time of the sharp transition from initial to final state becomes essentially unpredictable. The prototype system of this type is the chlorite-thiosulfate reaction (Nagypal and Epstein, 1986). Measurements of pH vs. time for five replicate experiments starting from the same initial concentrations are shown in Figure 15.8. For the first several minutes, all the curves are identical. The pH increases smoothly. In three of the curves, we observe a sharp drop in pH at approximately 3, 5, and 9 min in the other two, this decrease occurs at times greater than 20 min. When an acid-base indicator like phenolphthalein is added to the solution, the pH... 

AgN03(c9) + HiO(/). 4.113 (a) Check with litmus paper, test reactivity with carbonate, or mix with NaOH(c ) and demonstrate neutralization (use an acid-base indicator), (b) Titrate a known quantity of acid with standard NaOH( ) solution, (c) Visually compare the conductivity of an acid solution with that of a sodium chloride solution of the same molarity. 4.115 (a) The complete reaction is Pb (c9) + 2NO3 (09) -1- Na2S04( )... 

Properties of Selected Indicators, Mixed Indicators, and Screened Indicators for Acid-Base Titrations... 

Now by taking one more step we can view acid-base reaction in a broader sense. Suppose we mix aqueous solutions of ammonium chloride, NH4CI, and sodium acetate, CH3COONa. A sniff indicates ammonia has been formed. Reaction occurs,... 

The method developed by Epton [212,213] became the universally accepted method for the analysis of active matter of anionic and cationic surfactants. Epton s method, also known as the two-phase titration, is based on the titration of the anionic surfactant with cetylpyridinium bromide, a cationic surfactant, in the presence of methylene blue as indicator. A solution of the anionic surfactant is mixed with the indicator dissolved in dilute sulfuric acid, followed by further addition of chloroform, and then it is titrated with the cationic surfactant. Methylene blue forms a complex with the anionic salt that is soluble in chloroform, giving the layer a blue color. As the titration proceeds there is a slow transference of color to the water layer until the equivalence point. At the equivalence point colors of the chloroform and water layers are visually the same. On successive additions of titrant the chloroform layer lightens in shade and finally becomes colorless. 

When we mix two solutions the result is often simply a new solution that contains both solutes. However, in some cases the solutes can react with each other. For instance, when we mix a colorless aqueous solution of silver nitrate with a clear yellow aqueous solution of potassium chromate, a red solid forms, indicating that a chemical reaction has occurred (Fig. 1.1). This section and the next two introduce three of the main types of chemical reactions precipitation reactions, acid-base reactions, and redox reactions, all of which are discussed in more depth in later chapters. (The fourth type of reaction discussed in this text, Lewis acid-base reactions, is introduced in Section 10.2.) Because many chemical reactions take place in solution, particularly in water, in this section we begin by considering the nature of aqueous solutions. 

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