Phthalein indicators

A few drops of 1.0% alcoholic solution of phenol-phthalein indicator shall be added and the sample titrated with standard 0.1N ale KOH to the first pink end point permanent for 15 secs. 

M. D. Alexander, "Reactions of the Alkali Metals with Water A Novel Demonstration/ J. Chem. Educ., Vol. 69,1992,418. The reaction of sodium metal with water to produce an aqueous solution of sodium hydroxide and hydrogen gas is performed at the interface between paint thinner and the more dense water. Periodically, bubbles of hydrogen gas carry the sodium metal into the organic layer, temporarily stopping the reaction. The presence of the aqueous layer is shown by a phenol-phthalein indicator color change. 

See Carboxylic acids, Section 9.6.15, p. 1264.) If the substance is the free sul-phonic acid, dissolve 0.5 g of it in 5-10 ml of water, add a drop or two of phenol-phthalein indicator and neutralise with c. m sodium hydroxide solution. Then add 2-3 drops of 0.1 m hydrochloric acid to ensure that the solution is almost neutral (pale pink colour) under alkaline conditions the reagent tends to decompose to produce the evil-smelling phenylmethanethiol. 

Phthalein indicators Acid/base indicators derived from phthalic anhydride, the most common of which is phenol-phthalein. 

Add 100 cc. of H2O and distil until only about 50 cc. remains. Add 50 cc. of H2O and again distil until 3.5—50 cc. is left. Use extreme care to prevent the oxidizing mixture from burning and baking on the side of the distilling flask. The distillate should be water white if it is colored discard it and repeat the determination. Titrate the distillate with 0.1 N NaOH, using phenol-phthalein indicator. 1 cc. of 0.1 N NaOH = 0.0088 g. of amyl alcohol. 

In a titration of HNO3, you add a few drops of phenol-phthalein indicator to 50.00 mL of acid in a flask. You quickly add 20.00 mL of 0.0502 M NaOH but overshoot the end point, and the solution turns deep pink. Instead of starting over, you add 30.00 mL of the acid, and the solution turns colorless. Then, it takes 3.22 mL of the NaOH to reach the end point, (a) What is the concentration of theHN03 solution (b) Howmanymolesof NaOH were in excess after the first addition ... 

Using an analytical balance (Laboratory Methods C), weigh onto weighing paper three separate samples of about your calculated number of grams of the acid (PRE-LABORATORY QUESTION 5). Record your masses in TABLE 25.lA. It is not necessary to weigh exactly the amount calculated, but it is imperative that the mass of each sample be known precisely. After each sample has been weighed, transfer it quantitatively to a clean, clearly labeled 250-mL Erlenmeyer flask, and add 25 mL of distilled water and two drops of phenol-phthalein indicator. You will titrate the solution of NaOH you have prepared against each of these solutions of standard acid. 

The base consumption of a water is defined as that quantity of sodium hydroxide solution in mmol/1 which is consumed during titration up to certain pH values or to the transition points of certain indicators. If titration is carried out electrometrically to pH 4.3 or methyl orange or a mixed indicator are used, the base consumption given is the negative m value. If titration is carried out electrometrically to pH 8.3 or a phenol-phthalein indicator is used, base consumption is the negative p value. 

Most phthalein indicators are colorless in moderately acidic solutions and exhibit a variety of colors in alkaline media. The structural changes causing the color changes can be illustrated with the example of phenolphthalein, which is widely used in analytical practice (reaction [XI]). 

Various colour indicators may be used in oxyhalide systemsi i ii ii. Sulphon-phthalein indicators were investigated in phosphorus oxychloride i , thionyl chloride and acetyl chloride . The colour changes occurring reversibly at certain pci-values are independent both from the nature of the solvent and from the nature of the solutes changing the chloride ion activity of the solution. The solutions are slightly yellow in media of high chloride ion activity and red in solutions of low chloride ion activities. Red solutions are also formed in highly acidic aqueous solutions. 

Most Arrhenius bases are metals from Groups lA (1) and 2A (2), such as NaOH, KOH, LiOH, and Ca (OH) 2. The hydroxide ions (OH ) give Arrhenius bases common characteristics, such as a bitter taste and a slippery feel. A base turns litmus indicator blue and phenol-phthalein indicator pink. Table 14.3 compares some characteristics of acids and bases. 

Dissolve 5-20 g of well-mixed sample in 100 mL neutralized isopropanol. Add phenol-phthalein indicator and titrate with 0.1 M NaOH solution. If the sample is already alkaline, titrate instead with 0.2 M HCl solution. Calculations ... 

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