Phenolphthalein Color

Use a clean pipet to carefully add a drop of the standard NaOH solution to the solution in well Al, and stir with a toothpick. Pause for about 30 seconds and look down through the well for evidence of a persistent, light pink, phenolphthalein color that indicates the endpoint of the titration. Repeat this process with each drop until the endpoint is reached. Record the num-... 

Drop a few chunks of Dry Ice (solid CO2) into each cylinder. As CO2 bubbles through each cylinder, the solutions become acidic. First, pink phenolphthalein color... 

Procedure used in the 0.5—2.0 mg/cnt range The pH of 100 cm sample solution is adjusted to the range of phenolphthalein color change, as just described. Then 10 cm sodium chloride and 1 cm potassium chromate (10%) solutions are added and the titration is performed with diluted silver nitrate reagent (1 cm corresponds to 0.2 mg chloride). To obtain a blank reagent volume, 100 cm distilled water is titrated in the same way. The result is given by the Cl = 2(a-b) form in mg/dm , where a and b are the reagent volumes added to the sample and to the blank, respectively, and 2 is a factor needed to obtain the results in mg/dm for a sample volume 100 cm . 

Titration curve for 50.00 ml of 0.100 M CH3COOH with 0.100 M NaOH showing the range of pHs and volumes of titrant over which the indicators bromothymol blue and phenolphthalein are expected to change color. 

Detecting the presence of small, even invisible, amounts of blood is routine. Physical characteristics of dried stains give minimal information, however, as dried blood can take on many hues. Many of the chemical tests for the presence of blood rely on the catalytic peroxidase activity of heme (56,57). Minute quantities of blood catalyze oxidation reactions between colorless materials, eg, phenolphthalein, luco malachite green, luminol, etc, to colored or luminescent ones. The oxidant is typically hydrogen peroxide or sodium perborate (see Automated instrumentation,hematology). 

Upon completion of the addition, the mixture is agitated for 7 hours at ambient temperature. The solution is then poured into 3 liters of water/ice obtaining a clear solution of dark yellow color which is rendered alkaline upon phenolphthalein with 30% NaOH and extracted with ethyl ether to eliminate the majority of the pyridine. The mixture is filtered with active charcoal, the pH adjusted to 8 with hydrochloric acid 1 1 and extracted with chloroform to remove the 4,4 -dihydroxydiphenyl-(2-pyridyl)-methane which has not reacted. 

To approximately 20 ml of a 1 1 mixture of toluene (xylene) isopropyl alcohol, add 1 ml of oil-base mud and 75 to 100 ml of distilled water. Add 8 to 10 drops of phenolphthalein indicator solution and stir vigorously with a stirring rod (the use of a Hamilton Beach mixer is suggested). Titrate slowly with H SO, (N/10) until red (or pink) color disappears permanently from the mixture. Report the alkalinity as the number of ml of H SO (N/10) per ml of mud. Lime content may be calculated as... 

The objective of the titration is to determine the point at which reaction is complete, called the equivalence point. This is reached when the number of moles of OH- added is exactly equal to the number of moles of acetic acid, HC O originally present To determine this point, a single drop of an acid-base indicator such as phenolphthalein is used. It should change color (colorless to pink) at the equivalence point. 

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. 

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 14.6 and Example 14.8, it should be clear that the indicator used in this titration must change color at about pH 9. Phenolphthalein (end point pH = 9) is satisfactory. Methyl red (end point pH = 5) is not suitable. If we used methyl red, we would stop the titration much too early, when reaction is only about 65% complete. This situation is typical of weak acid-strong base titrations. For such a titration, we choose an indicator that changes color above pH 7. 

Electrolysis of potassium iodide (Kl) solution. The electrolysis of aqueous Kl is similar to that of aqueous NaCI. The cathode reaction (left/ is the reduction of water to H2(g) and OH-, as shown by the pink color of phenolphthalein indicator in the water. The anode reaction fright) is the oxidation of l (aq) to Ijfaq), as shown by the brown color of the solution. 

Analytical. It can be titrated with std base to a salmon colored phenolphthalein endpoint and can be quanty pptd from aq solns with tetraphenylarsonium chloride KSp of the complex in w is 6.9 x 10 9 (Ref 22). This procedure can be adapted to the analysis of compds, such as bis-(trinitroethyl) urea, which regenerate... 

NOTE Acid phosphates and SHMP may attack chemical tanks and associated equipment, so acid-resistant equipment should be specified. Alternatively, the addition of caustic up to a pH level of 8.2 to 8.3 (the production of a pink color when tested with phenolphthalein) provides adequate protection. A further alternative is to add neutralizing amine to the tank. 

In a typical acid—base titration, the analyte is a solution of a base and the titrant is a solution of an acid or vice versa. An indicator a water-soluble dye (Section J), helps us detect the stoichiometric point, the stage at which the volume of titrant added is exactly that required by the stoichiometric relation between titrant and analyte. For example, if we titrate hydrochloric acid containing a few drops of the indicator phenolphthalein, the solution is initially colorless. After the stoichiometric point, when excess base is present, the solution in the flask is basic and the indicator is pink. The indicator color change is sudden, so it is easy to detect the stoichiometric point (Fig. L.3). Toolbox L.2 shows how to interpret a titration the procedure is summarized in diagram (3), where A is the solute in the titrant and B is the solute in the analyte. 

FIGURE 11.10 The stoichiometric point of an acid base titration may be detected by the color change of an indicator. Here we see the colors of solutions containing a few drops of phenolphthalein at (from left to right) pH of 7.0, 8.5, 9.4 (its end point), 9.8, and 12.0. At the end point, the concentrations of the conjugate acid and base forms of the indicator are equal... 

One common indicator is phenolphthalein (Fig. 11.10). The acid form ol this large molecule (3) is colorless its conjugate base form (4) is pink. The structure of the base form of phenolphthalein allows electrons to be delocalized across all three of the benzenelike rings of carbon atoms, and the increase in delocalization is part of the reason for the change in color. The pFCIn of phenolphthalein is 9.4, and so the end point occurs in slightly basic solution. Litmus, another well-known indicator, has pkln = 6.5 it is red for pH < 5 and blue for pH > 8. 

Alkalinity is measured by acid-base titration with methylorange or phe-nolphthalein as indicator. Phenolphthalein changes color at pH 8.3, whereas methylorange changes color at pH 4.3. At pH 8 the neutralization of the strong alkali ingredients like NaOH is essentially complete. Further reduction of the pH to 4 will also measure carbonates and bicarbonates. Colorimetric tests and glass electrode systems are used to determine pH. 

What color is phenolphthalein in an acidic solution What color is phenolphthalein in a basic solution Why is a solution of phenolphthalein used in this activity ... 

Indicators are chemical dyes that change color with a change of pH. Litmus paper and phenolphthalein are two common indicators used in acid-base reactions. They are chosen because they change color at or very near solution neutrality. Litmus paper is red in acidic solutions and blue in basic solutions. Phenolphthalein is colorless in acidic solutions and turns red in basic solutions. 

Compare the color of phenolphthalein in acidic and basic solutions. 

Fluoran compound used as leuco dye needs to have substituent(s) on the xanthene moiety to develop color, though fluoran 1 itself is prepared as a by-product in the synthesis of phenolphthalein from phenol and phthalic anhydride. 

Phenolphthalein is another acid-base indicator. It is often used by magicians (and chemistry teachers) to perform a trick that turns water into wine. In acidic and neutral conditions, phenolphthalein is colorless and looks like water. A pH of approximately 8.3, however, turns phenolphthalein a deep reddish-violet color. In basic conditions, phenolphthalein looks like red wine. 

The reason the two forms of phenolphthalein are different colors is because the chemical reaction changes the shape of the phenolphthalein molecule. In other words, the molecule has a different shape under acidic conditions than it does under basic conditions. The different shapes absorb and reflect different wavelengths of light. Our eyes see different wavelengths of visible light as different colors. 

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. 

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