Thus any error or bias less than 0.33 parts per thousand is insignificant. Theory. Phenolphthalein, which changes from colorless to pink when enough NaOH has been added to react with all the KHP present, is used as an indicator for the . To learn more, see our tips on writing great answers. Then the original molarity can be calculated by dividing through with the initial volume. A chemical reaction isn't always visible to the human eye, but sometimes it results in an impressive color change and makes science experiments more fun to witness. Federal government websites often end in .gov or .mil. The pKA values of phenolphthalein was found to be 9.05, 9.50 and 12 while that of phenolsulfonphthalein are 1.2 and 7.70. The University of Waterloo acknowledges that much of our work takes place on the traditional territory of the Neutral, Anishinaabeg and Haudenosaunee peoples. What is the difference between the titration of a strong acid with a strong base and that of the titration of a weak acid with a strong base? Consider if the pKa of the acid was 2. $$k_{Ind} = [\mathrm{H_3O^+}] \tag{3}$$, If you substitute (3) into (1) and take the negative logarithm to base 10 you get, $$\mathrm{pK_A} - \mathrm{pK_{Ind}} = -\log\frac{[\mathrm{A^-}]}{[\mathrm{HA}]} = 4.4 - 9.4 = -5.2$$. $$\mathrm{pH} = \mathrm{p}K_\mathrm{b} + \log \frac{\ce{In}}{\ce{HIn}}$$. After pouring beakers 2, 3, 4 back into the pitcher it give a pink solution. This amount will be needed for the three trials. Methyl orange turns red in acidic solutions and yellow in neutral or alkaline solutions. The overlap creates a 'pi bond' which allows the electrons in the p orbital to be found on either bonded atom. hbbd```b``f \"9H`0D`5"dXD0+d M*c@= Hta`bd`qP>0 r
Your Safer Source for Science. The concentration ofOH- ions is very large compared to the concentration of phenolphthalein. The The first beaker contain acetic acid and is skipped over at first. Citric acid1is produced by the fermentation of sugars (> 1 M tonne per year) for use in beverages and foods (70%); in detergents (20%); and in cosmetics, pharmaceuticals and other chemicals (10%). \[ HCl_{(aq)} + NaOH_{(aq)} \rightarrow H_2O_{(l)} + Na^+ + Cl^-\], The following equation can then be derived, \[ X= (0.1\; M \;\; NaOH) (10\;mL) \left(\dfrac{1\;L}{1000\; mL} \right) \left( \dfrac{1\;mol\; NaOH}{1\; mol \; OH^-} \right)\], \[ \dfrac{0.0010\; mol\; HCl}{0.050\; L} = 0.020\;M \;HCl\]. kinetics system. It is produced as a crystalline solid, either anhydrous, or as a monohydrate, and is available in either form at low cost. Phenolphthalein + sodium carbonate and phenolphthalein + sodium bicarbonate [closed] Ask Question . When you shake the solution in a half-filled bottle, oxygen goes into the solution, oxidizing the methylene blue and turning the solution blue. 289 0 obj
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Handle and clean up solid citric acid as you would solid sodium hydroxide. If a large amount of indicator is used, the indicator will effect the final pH, lowering the accuracy of the experiment. Thus, there will be a visible and clear-cut indication of the occurrence of
The pattern will eventually disappear again because of the reaction with carbon dioxide. Elmhurst College: Acid and Base Indicators, Purdue University: The Blue Bottle Demonstration. In other titrations, the endpoint may be marked by a change in electrical conductivity of the reaction mixture, by the formation of a precipitate, or by a variety of other means. If it's similar then OK. Data and calculations for a typical acid-base titration are shown in Table 11.5 Notice that three trials were run - a standard procedure to check the precision of titration. If any extra hydroxide
The author thanks Randy Travis, technologist of the Department of Chemical, Environmental, and Biotechnology of Mohawk College, for his invaluable help. The simplified reaction is: H+ + OH- HOH. The result is that as the equivalence point is approached, even with swirling, the pink-red colour appears where the drops of titrant enter the titration flask and persists, at first for fractions of a second, then longer and longer, until a faint pink colour can be seen throughout the solution that persists for at least one minute (seeQuestion 3). Why don't we use the 7805 for car phone chargers? Phenolphthalein ion in concentrated sulfuric acid is orange red due to sulfonation. Whereas most dyes do not change color with the amount of acid or base present, there are many molecules, known as acid - base indicators , which do respond to a change in the hydrogen ion concentration. Some titrations requires the solution to be boiled due to the \(CO_2\) created from the acid-base reaction. Record the mass of the bottle and its contents. The endpoint is \(pH= 7\) so litmus, with a pKa of 6.5 is chosen. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. 2. Titration reactions are not always acid-base reactions. in acidic solutions and pink in basic solutions. It is a weak acid, which can lose H+ ions in solution. titrations. The reagent (titrant) is the solution with a known molarity that will react with the analyte. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? The fading of phenolphthalein is a second order reaction, because the reaction of phenolphthalein (abbreviated P) with hydroxide (OH-) to the colorless compound POH leads to changes in the concentration of both OH- and phenolphthalein: where k is a positive number with unit s-1. Asking for help, clarification, or responding to other answers. HDM0AZoD^16"hTqv+`&.()1[8P]i`G&22R&=\A? It readily absorbs moisture until it dissolves. What's the cheapest way to buy out a sibling's share of our parents house if I have no cash and want to pay less than the appraised value? The .gov means its official. In a highly basic solution, phenolphthalein's slow change from pink to colorless as it is converted to its Ph(OH)3 form is used in chemistry classes for the study of reaction kinetics. The pKa of phenolphthalein is 9.4 so almost half of the phenolphthalein would converted to the colored form so the color change should be very detectable at that point. phenolphthalein indicator. In the ink, it is mixed with sodium hydroxide, which reacts with carbon dioxide in the air. Further loss of proton in higher pH occurs slowly and leads to a colorless form. An indicator is usually some weak organic acid or base dye that changes colors at definite pH values. 5.7D you learned about organic compounds called indicators that have one
Then I titrate NaOH solution into it. { Acid_and_Base_Indicators : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", PH_Indicators : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, { Acid : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Acids_and_Bases_in_Aqueous_Solutions : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Acid_and_Base_Indicators : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Acid_Base_Reactions : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Acid_Base_Titrations : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Buffers : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Buffers_II : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Ionization_Constants : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Monoprotic_Versus_Polyprotic_Acids_And_Bases : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, [ "article:topic", "Indicators", "showtoc:no", "license:ccbyncsa", "licenseversion:40", "author@Charles Ophardt" ], https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FPhysical_and_Theoretical_Chemistry_Textbook_Maps%2FSupplemental_Modules_(Physical_and_Theoretical_Chemistry)%2FAcids_and_Bases%2FAcid_and_Base_Indicators%2FAcid_and_Base_Indicators, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), Molecular Basis for the Indicator Color Change, For phenolphthalein: pH 8.2 = colorless; pH 10 = red, For bromophenol blue: pH 3 = yellow; pH 4.6 = blue. As long as unreacted hydrogen ions remain in solution, the solution
Phenolphthalein is a weak acid and is colorless in solution although its ion is pink. $$k_{Ind} = \frac{[\mathrm{H_3O^+}] [\mathrm{Ind^-}]}{[\mathrm{HInd}]} \tag{2}$$, The color change is around the point where the concentrations $[\mathrm{HInd}]$ (colorless) and $[\mathrm{Ind^-}]$ (colored) are equal, i.e. If phenolphthalein is added
What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? A Litmus indicator solution goes red in acidic solutions, blue in alkaline solutions and purple in neutral solutions. Repeat the titration procedure. A Litmus indicator solution goes red in acidic solutions, blue in alkaline solutions and purple in neutral solutions. . Bethesda, MD 20894, Web Policies As OH- ions are added, they are consumed by the excess of acid already in the beaker as expressed in the above equation. Explain. Thus all in all no blank should be needed. You want a difference between the pKa's of the acid and the indicator. But how can I conclude mathematically that this is a correct choice? I can calculate the $K_\mathrm{b}$ of $\ce{NaOH}$ from the above data. At Mohawk College we store the dropper bottles containing the sodium hydroxide solution for long periods with no apparent ill effects. If excess base is present at the end of an acid-base titration, the pink phenolphthalein color fades if the solution is allowed to stand for a while. No noise means we're only measuring signal.). internal referencing method was shown to be essential in improving What do hollow blue circles with a dot mean on the World Map? The reaction between hydroxide ions and hydrogen ions is rapid and complete; thus, the second requirement for an analytical titration is met. For trial 1 transfer some of the solution as carefully as you can into the 10 mL graduated cylinder, up to the 5.0 mL line, using the dropper pipet to adjust the bottom of the meniscus to the line. Table 11.4 lists three indicators that could be used in acid-base
The pH of 0.033 M citric acid is about 2.2, which is slightly higher than that of lemon juice.4The 0.1 M sodium hydroxide and the phenolphthalein indicator are more hazardous. Esterification is another type of liquid phase thermoreversible reaction, which occurs between a carboxylic acid (R 1 -COOH) and alcohol (R 2 -OH) to form an ester (R 1 -COO-R 2 ) and water.. the endpoint. Is a downhill scooter lighter than a downhill MTB with same performance? It only takes a minute to sign up. When applied, the basic spackling material retains a pink color; when the spackling has cured by reaction with atmospheric carbon dioxide, the pink color fades.[8]. Phenolphthalein as a indicator for the titration of benzoic acid, Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Continue until the criterion of successful completion is achieved. That would mean weighing out about 3.0 millimoles of benzoic acid (0.37 grams) which would be dissolved in 25 ml of distilled water. ), The full method and a sample titration should be demonstrated for novices. Choosing an indicator with a pKa near the endpoint's pH will also reduce error because the color change occurs sharply during the endpoint where the pH spikes, giving a more precise endpoint. More confinement makes the light absorbed more blue, and less makes it more red. Sodium hydroxide is a base, so when you add phenolphthalein, the solution turns pink. In comparison to using hydro-chloric acid solutions, using solid citric acid and its solutions in water is safer and more convenient. It is found that the indicator changes color once 31.25 mL of the sodium hydroxide Universal Indicator, which is a solution of a mixture of indicators is able to also provide a full range of colors for the pH scale. solution. As far as I have understood, I have to compare the $\mathrm{p}K_\mathrm{b}$ of sodium benzoate with the $\mathrm{p}K_\mathrm{ind}$ of phenolphthalein. Using the pKb (14 -pKa) of the acid is just wrong. and transmitted securely. I'm learning and will appreciate any help. government site. the contents by NLM or the National Institutes of Health. Is there such a thing as "right to be heard" by the authorities? Empty the cylinder totally, by waiting until the last drops fall. One mole of aqueous Hydrogen Chloride [HCl] and one mole of aqueous Sodium Hydroxide [NaOH] react to form one mole of aqueous Sodium Chloride [NaCl] and one mole of liquid Water [H2O] A few drops of phenolphthalein solution in 0,10M NaOH cup, pink liquid. Add. That would introduce a significant blank value which would then need to be corrected for. To find out more, please proceed to download the application note below. Caustic soda, ie sodium hydroxide, used in the manufacture of soap. The notion here is that if 0.01 ml of titrant would change the indicator then we can ignore the necessity of using a blank. Legal. The molecule absorbs in the ultraviolet, and this form of phenolphthalein is colorless. Careers, Unable to load your collection due to an error. [2], Phenolphthalein's common use is as an indicator in acid-base titrations. For other related dyes in the phthalein family, see, 3,3-Bis(4-hydroxyphenyl)-2-benzofuran-1(3, 3,3-Bis(4-hydroxyphenyl)isobenzofuran-1(3, InChI=1S/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H, InChI=1/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H, O=C1OC(C2=C1C=CC=C2)(C3=CC=C(C=C3)O[H])C4=CC=C(C=C4)O[H], Except where otherwise noted, data are given for materials in their, Calcium release activated channel Structure, "Spectrophotometric Analysis of the Relationship between Dissociation and Coloration, and of the Structural Formulas of Phenolphthalein in Aqueous Solution", "Phenolphthalein Exposure Causes Multiple Carcinogenic Effects in Experimental Model Systems", 10.1002/(SICI)1098-2280(1998)31:2<113::AID-EM3>3.0.CO;2-N, "3 Versions of Ex-Lax Are Recalled After F.D.A. A reduced form of phenolphthalein, phenolphthalin, which is colorless, is used in a test to identify substances thought to contain blood, commonly known as the KastleMeyer test. The solution to this problem should be set up in the form of Table 11.5. $$k_A = \frac{[\mathrm{H_3O^+}] [\mathrm{A^-}]}{[\mathrm{HA}]} \tag{1}$$, and second the (simplified) protolysis of phenolphthalein, $$\ce{HInd + H2O <=> H3O+ + Ind-}$$ In strongly basic solutions, phenolphthalein is converted to its In(OH)3 form, and its pink color undergoes a rather slow fading reaction[6] and becomes completely colorless when pH is greater than 13. A photodiode array (PDA) spectrophotometer was used to study the fading reaction of phenolpthalein in dilute sodium hydroxide solution. It was discovered in 1871 by Adolf von Baeyer. In comparison to titrations with a strong acid such as hydrochloric acid, the diluted weak acid mops up the base in the drops of added titrant more slowly. This chemical reaction is hydrated copper carbonate, and a famous example of it is the Statue of Liberty. In 55 ml of solution that yields a pH of 9.3. Sodium hydroxide is a base, and it was in the pitcher at the beginning, so when added to the phenolphthalein in beakers 2 and 4, it turned pink (top half of the graphic). What is this brick with a round back and a stud on the side used for? In reality the color change should be detectable at a pH of about 8.5, so much less than half of the indicator will react to make the colored form. Acid and Base Indicators is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Charles Ophardt. Sample Calculation . spectrophotomer. endstream
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With the balanced equation of the acid-base reaction in question to find the moles of unknown substance. The drop count can serve as a guide to speed up the repeat titrations. The density of a 0.125 M NaOH solution at 20 C is 1.0039 g/mL.6For student calculations the density of a 0.1 M NaOH solution is so close to unity in g/mL units that the mass values of titrations in g units can be used as volumes in mL units without significant error. Storage of citric acid solution may not be advisable, since it may well support microbiological life. Plant pigments in flowers and leaves also behave in this fashion. The peak and light blue highlights show the range in which the color changes will occur based on the amount of titrant added. sharing sensitive information, make sure youre on a federal Use equilibrium principles to explain the color change for phenolphthalein at the end of the demonstration. If the sample contains hemoglobin, it will turn pink immediately upon addition of the peroxide, because of the generation of phenolphthalein. So let's calculate pH at which: or at $\text{pH(99.9% conversion)} = \mathrm{p}K_a + 3.00$. Therefore the OH- concentration can be considered as constant and the reaction is a "pseudo" first order. In 55 ml of solution that yields a pH of 9.3. The very slow fading of the colour of the phenolphthalein indicator is blamed on carbon dioxide in the air reacting with the hydroxide ion in the solution. This reasoning is totally wrong. Swirl to dissolve the KHP completely. Reaction ofphenolpthalein with sodium hydroxide Whenphenolpthalein reacts with dilute sodiumhydrox-ide, the process can be described mainly as reversible reaction of the coloured form R2-of . Our main campus is situated on the Haldimand Tract, the land granted to the Six Nations that includes six miles on each side of the Grand River. Since theses are dilute solutions and are mostly water, assume that the densities of the solutions and the specific heat capacities of the solutions are approximately 1.0 g/ml and 4. . Which salt is formed by the reaction of sodium hydroxide? Geez simply compare pKb of acid with pKind. Phenolphthalein: 0.1% dissolved in absolute ethyl alcohol (3) Standard sodium hydroxide solution. The indicator should also have a pKa value near the pH of the titration's endpoint. the quality of data obtained by a single beam PDA 2023 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. . The fading of phenolphthalein is a second order reaction, because the reaction of phenolphthalein (abbreviated P) with hydroxide (OH-) to the colorless compound POH leads to changes in the concentration of both OH-and phenolphthalein: P + OH - POH. Molarity of KOH: 0.129 M ( 0.129 mmol KOH/mL solution), (These data are obtained by subtracting the buret reading given in the
The image on the right is submicroscopic view of the titration reaction featuring C2H4O2(aq), which is partially dissociated and NaOH (aq) that is completely dissociated into Na+(aq) in purple and OH-(aq). How will the experimenter know when
Why educational research matters to you: Rote vs meaningful learning, http://www.sigmaaldrich.com/catalog/product/sial/c0759?lang=en®ion=US, http://www.sigmaaldrich.com/catalog/product/sial/c7129?lang=en®ion=US, https://www.boreal.com/store/catalog/product.jsp?catalog_number=9448906, http://www.fibregarden.ca/shopfg/index.php?main_page=product_info&cPath=1_135_139&products_id=658, http://www.engineeringtoolbox.com/acids-ph-d_401.html, http://www.uclmail.net/users/dn.cash/articles.html, http://www.uclmail.net/users/dn.cash/GravTitr3.pdf, http://www.uclmail.net/users/dn.cash/GravTitr2.pdf, Sufficient volume of 0.1 M NaOH (4.0 g/L), Sufficient volume of 0.033 M citric acid (6.4 g/L), Sufficient volume of phenolphthalein indicator in small labeled dropper bottles, Transfer about 10 mL of the citric acid solution into a. Transfer the 5.0-mL sample of citric acid solution for trial 1 from the cylinder into a 125-mL Erlenmeyer flask. If we assume half of the base reacts with the indicator we still have a pH of about 9.0 for the solution. The 2-bromo-2-methylpropane is in such large excess that its concentration may be considered to be virtually constant. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. The rate law for this reaction is: rate = v = - k [OH-] * [P] For example, putting red food coloring and blue food coloring in a beaker of water results in purple water, but no chemical reaction has occurred. This is a reversible redox reaction. Built in 1886, the Statue of Liberty was initially reddish-brown. A titration is an experiment where a volume of a solution of known concentration is added to a volume of another solution in order to determine its concentration. For example a analyte that is a weak base would require an indicator with a pKa less than 7. It belongs to the class of dyes known as phthalein dyes. So, $\mathrm{p}K_\mathrm{ind}$ lies in between the values $\mathrm{p}K_\mathrm{b} \pm 1$. The Full Text of this article is available as a PDF (460K). The neutralization reaction with sodium hydroxide has 3 to 1 stoichiometry as illustrated by the balanced complete neutralization equation. When two or more substances combine, they create one or more new substances, which sometimes have different molecular structures from the original substances, meaning they absorb and radiate light in different ways, leading to a color change. rate constants and the concentration-time profile of the reaction. On the report sheet, record the initial reading of the NaOH solution in the buret to the nearest Citric acid is a relatively strong weak acid, but no special precautions are required for its use. Titrate the solution in the Erlenmeyer flask by adding drops of solution from the. How are electrons confined in phenolphthalein? This estimation involves titration of a weak acid that is oxalic acid against a strong base sodium hydroxide and phenolphthalein is the indicator of choice. The reaction goes to completion and is suitable for analytical titrations: 3 NaOH (aq) . A few drops of alcohol, then a few drops of phenolphthalin, and finally a few drops of hydrogen peroxide are dripped onto the sample. What is the chemical reaction. A false positive can result from the presence of substances with catalytic activity similar to hemoglobin. Accessibility StatementFor more information contact us atinfo@libretexts.org. Both solids are stable and remain free-flowing in the bottle after many years of storage. When all HCl has reacted with NaOH the solution is colored pink. The precision of the volume measurement of the graduated cylinder lies between 5.0 mL and 5.00 mL. The doubly deprotonated (In2-) phenolate form (the anion form of phenol) gives the familiar pink color. We can't ever remove all of the $\ce{HA}$ form since we can always calculate the relative amounts of $\ce{HA}$ and $\ce{A^-}$ based on the pH. The target factor analysis (TFA) procedure, react with acids, in which case a diprotic acid named phthalic acid, H 2 C 8 H 4 O is produced.) (a triprotic acid) 192.1 g / mol. $K_\mathrm{b}$ of sodium benzoate $=\frac{K_\mathrm{w}}{K_\mathrm{a}}=1.59\times 10^{-10}$, $\mathrm{p}K_\mathrm{b}$ of sodium benzoate $=9.79$, $\mathrm{p}K_\mathrm{ind}$ of phenolphthalein $=9.4$.
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