Citric Acid titration

Since citric acid is a triprotic weak acid, we must first decide to which equivalence point the titration has been carried. The three acid dissociation constants are... 

If the weak acid is monoprotic, then the FW must be 58.78 g/mol, eliminating ascorbic acid as a possibility. If the weak acid is diprotic, then the FW may be either 58.78 g/mol or 117.6 g/mol, depending on whether the titration was to the first or second equivalence point. Succinic acid, with a formula weight of 118.1 g/mol is a possibility, but malonic acid is not. If the analyte is a triprotic weak acid, then its FW must be 58.78 g/mol, 117.6 g/mol, or 176.3 g/mol. None of these values is close to the formula weight for citric acid, eliminating it as a possibility. Only succinic acid provides a possible match. 

Analytical and Test Methods. Aqueous titration with 1 AiNaOH remains the official method for assaying citric acid (39,40). Although not citrate-specific, the procedure is satisfactory in the absence of interfering substances. Low concentrations of citric acid can be deterrnined by a... 

Testing is undertaken by several methods, including chloroform extraction and use of a sulfonphthalein dye (absorbance of yellow-colored complex using bromophenol blue and bromocresol green) or the use of eosin (sodium tetrabromofluorescein) solution in acetone and tetrachloroethane solvent. After shaking with a citric acid buffer and eosin addition, upon standing the lower layer turns pink if filmer is present. Subsequent titration with Manoxol OT (sodium dioctyl sulfosuccinate) quantifies the filmer, with loss of the pink color indicating the end point. 

Initial hydrolysis would therefore lead to further hydrolysis and pH drop in storage tanks, resulting in a product that is difficult to recover and may cause irreparable damage (corrosion) in tanks, pipelines, and pumps. Therefore the pH must be kept high (9-11) to avoid acid material entering bulk storage (steep titration curve). If for product formulation requirements a product of pH 6-7 is essential, the use of buffers, e.g., phosphoric acid or citric acid, is recommended. 

Potassium trisiamylborohydride, 20 605 Potassium winchite, 3 289 Potassium-zirconium carbonate, 26 637 Potato branching enzyme, 12 493 Potatoes, citric acid in, 6 632t Potato fungicide, 13 57 Potato starch, 4 724t Potential energy diagrams, 10 118-119 Potential gum test, 12 400 Potentiated toxic effects, 25 214 Potentiometric measurements, 14 612 Potentiometric titrations, 9 585-58 ... 

As long as the soda pop is carbonated, the carbonic acid is present along with the phosphoric acid, although at a much smaller concentration. Citric acid may also be present, but at a smaller concentration. The carbonic acid may be eliminated by degassing to remove the carbon dioxide. Your instructor may ask you to obtain titration curves (step 4 below) for both as received samples and... 

First obtain the complete titration curve for the sample. This will involve cautious addition of the NaOH around the inflection points so that you can carefully track the sharp change in the pH at these points. Alternatively, you may choose to use a computer for data acquisition, as in Experiment 18, Part B. Phosphoric acid (H3P04) has three hydrogens to be neutralized. The third hydrogen is lost with only a slight change in pH, however, so you may only see two inflection points. If citric acid is also present (check the can label), there maybe other inflection points as well. 

From your titration curve, decide which inflection point you want to use for the equivalence point for the titrations in step 6, keeping in mind the possible interference from citric acid. 

The historical development of titration calorimetry has been addressed by Grime [197]. The technique is credited to have been born in 1913, when Bell and Cowell used an apparatus consisting of a 200 cm3 Dewar vessel, a platinum stirrer, a thermometer graduated to tenths of degrees, and a volumetric burette to determine the end point of the titration of citric acid with ammonia lfom a plot of the observed temperature change against the volume of ammonia added [208]. The capabilities of titration calorimetry have enormously evolved since then, and the accuracy limits of modern titration calorimeters are comparable to those obtained in conventional isoperibol (chapter 8) or heat-flow instruments (chapter 9) [195,198],... 

This corresponds to titrating citric acid with NaOH. The titration curve is very nearly linear from pH 2.2 to about pH 5.5 with a slope of 3.60. The effects of the three functional buffer groups of citric acid are smeared so that no S-shape or inflection points are apparent. 

Citric acid extractant - dissolve 10 g citric acid monohydrate in water, make up to 500 ml and adjust to 20°C. This is sufficient for one sample -for a number of samples, increase quantities as appropriate. The concentration may be checked by titrating 10 ml reagent against 0.1 M NaOH using phenolphthalein indicator, when the titre should be 28.55 ml. 

Weak acid/strong base titration is used in the pharmacopoeial assays of benzoic acid, citric acid, chlorambucil injection, mustine injection, nicotinic acid tablets and undecanoic acid. 

Wang has determined citric acid and procaine in Xiaozhi injectable (an anti-hemorrhoid agent) by two-phase titration [81]. With constant shaking, a mixture of 1 1 1 2 Xiaozhi solution - water - chloroform -ethanol was titrated against 0.1 M sodium hydroxide to the phenolphthalein end point, thus obtaining the citric acid content. Dilute nitric acid was then added to the solution until the pink color disappeared, and the solution titrated against 0.1 M silver nitrate (with 5 drops of... 

Wang has determined procaine hydrochloride in the presence of citric acid [82]. To the sample (prepared as 5 mL of aqueous solution) were added 5 mL of water, 1 mL of 0.1 M hydrochloric acid, and 200 mg potassium bromide. The resulting solution was titrated with 0.1 M sodium nitrite, ultimately yielding the total content of procaine hydrochloride and citric acid. 

The titration curve for H3P04 using NaOH is shown in Figure 5.8. Citric acid is also triprotic while carbonic acid (H2CQ3) is diprotic. 

In a definitive series of experimental investigations H. N. Wilson showed that the quinolinium salt, (C isNJ fPCV I2M0O3]3- was anhydrous, contained exactly 12 moles of molybdenum trioxide per mole of phosphate, that the precipitate had a negligible solubility and could be dried to constant weight in two hours at 105 °C. This precipitate also lent itself to a precise alkalimetric titration. In the presence of citric acid interference by silica was inhibited so that the method was admirably suitable for the analysis of basic slags or fertilizers.34... 

Introduction. Citric acid in citrus juices may be determined according to the Methods of Analysis as given in the AOAC (7). However, analysts who run a large number of tests daily have altered the method to speed up the titration and make calculations easier. One of these alterations is to use 0.3125 N sodium hydroxide rather than 0.1 N alkali. The use of the higher normality alkali is desirable especially when titrating samples of high density concentrates. It is almost imperative when titrating lemon concentrates. 

A. Multiply the number of milliliters of standard alkali used in the titration by 0.2. The result will be percent by weight of anhydrous citric acid by weight of concentrate. Example 18.9 ml of standard alkali X 0.2 = 3.78% anhydrous citric acid. 

Citric acid, like other acids, tastes sour and can cause orange juice to be sour. Assuming that citric acid is the only acid present, a liter-size sample is titrated with 193 mL of 0.75 M NaOH. Also, assuming that citric acid is the only component in the juice reacting, what is the normality of citric acid present ... 

In warmer vintages in the North Coast, grapes, especially riper grapes at 23°-24° Brix, may be low in titratable acidity. Desirable levels of acidity in white juice prior to fermentation range from 0.7 to 1.0 g/100 mL, depending on final wine composition and wine style desired. Tartaric acid is used most commonly for acidulation and often is added to juice prior to fermentation. Malic acid and citric acid also are used for acidulation. 

Zhang et al. determined ciprofloxacin lactate in injectable solutions by acid dye biphasic titration [5]. A 200 mg dried sample was dissolved in and diluted with water to a volume of 100 mL, and then a 2 mL aliquot of the solution was mixed with 10 mL Na2HP04/citric acid buffer (pH 7) and 15 mL CHC13. This solution was titrated with 0.5 mM-bromothymol blue, with agitation, until a light-blue end-point appeared in the aqueous phase. Recoveries were 99.9-102%, with a relative standard deviation (n = 4) of 0.22-0.24. 

Acidity (as citric acid) Dissolve 32 g of sample, accurately weighed, in 30 mL of alcohol neutralized to bromothymol blue, and titrate with 0.1 A sodium hydroxide. Not more than 1.0 mL is required. 

The enzyme assay components including internal standards are resolved within 3 minutes on a 4.6 mm x 3.3 cm, 3 gm reversed-phase ODS column (Perkin-Elmer). The mobile phase contained 0.100 M citric acid, 0.50 mW tetrapentylammonium chloride (an ion-pairing agent), 50 fiM EDTA, and 12.5% acetonitrile (v/v) titrated to pH 4.70 with NaOH. Eluted compounds were detected with an electrochemical detector. The separation obtained is shown in Figure 9.16. 

To provide a sensing matrix that can use the least acidic proton on citric acid, polyethyleneimine, with p/sTa =11, serves as the matrix onto which citric acid wiU be ionically tethered to the polymer s backbone. Titration of a solution of polyethyleneimine with a solution of citric acid to a pH of 6.0 produces a polymer solution of polyetheneimine-citric acid, where the lone least-acidic proton is on the citric acid available for reaction with the ammonia, while the other two are bound to the amines of the backbone of the polyethyleneimine. For a reference arm, another solution of polyethyleneimine is titrated with a solution of citric acid to a pH of 8, thereby yielding a solution in which all the protons of the citric acid are on the polyethyleneimine backbone. The first solution, pH 6.0, is deposited on the sensing arm of a silicon nitride waveguide. The second solution, pH 8.0, is deposited on the reference... 

The end point of a titration should not come as a surprise to the analyst. Before a single drop of titrant has been added, an estimate of the endpoint volume should be carried out. For a simple forward titration, like the citric acid example above, the approximate titre is given by... 

Students often prefer to perform simple calculations, like the direct titration of citric acid, using absolute molarities of titrant instead of deriving the equivalent and making use of factors. The procedure adopted is to convert the volume of titrant required to a number of moles and, from the balanced chemical equation, relate this to the number of moles of reactant used in the assay. This number is then converted into a weight and the... 

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