Lemon juice, acid concentrations

Because hydronium concentrations usually involve negative powers of ten, chemists use a negative log scale in expressing these concentrations. Equation defines the pH scale of acid concentration pH = - log [H3 O ] The pH of a solution is obtained by taking the logarithm of the hydronium ion concentration and then changing the sign. For example, the pH of pure water is pH = - log [H3 O ] = - log (1.0 X 10 ) — -(-7.00) — 7.00 The reverse conversion from pH to [H3 O ] uses powers of 10. For example, lemon juice has a pH of about 2.0 ... 

In 1795 the British admiralty finally mandated a ration of concentrated lime or lemon juice for all British sailors (hence the name limeys ). Scurvy continued to be a problem in some other parts of the world until 1932, when Hungarian scientist Albert Szent-Gyorgyi, and W. A. Waugh and C. G. King at the University of Pittsburgh, isolated and synthesized ascorbic acid. 

Figure 6-7 pH of various substances. [From Chem. Eng. News. 14 September 1981.] The most acidic rainfall (Box 15-1) is a stronger acid than lemon juice. The most acidic natural waters known are mine waters, with total dissolved metal concentrations of 200 g/L and sulfate concentrations of 760 g/L The pH of this water, -3.6, does not mean that [H ] = 103- M ... 

The concentration of H30+ ions in a sample of lemon juice is 2.5 X 10 3 M. Calculate the concentration of OH- ions, and classify the solution as acidic, neutral, or basic. 

The acidity of lemon juice is derived primarily from citric acid (H3Cit), a triprotic acid. What are the concentrations of H3Cit, H2Cit-, HCit2-, and Cit3- in a sample of lemon juice that has a pH of 2.37 and a total concentration of the four citrate-containing species of 0.350 M ... 

Sn+, Fe+3, Sn+, and Al+. These investigators reported that 3-deoxyglucosone and 5-hydroxymethylfurfural were intermediates in the browning of concentrated lemon juice that occurred when the concentrate was diluted to single-strength juice with a sucrose solution. They concluded that amino acids had a role in the browning (51). 

The acid in concentrated lemon juice for manufacture is expressed as grams per liter. The easiest way to determine the acid in this product is to determine the acid in grams per 100 grams and convert this to grams per liter, e.g. 

Citric acid occurs naturally in a number of plant species and may be extracted from lemon juice, which contains 5-8% citric acid, or pineapple waste. Anhydrous citric acid may also be produced industrially by mycological fermentation of crude sugar solutions such as molasses, using strains of Aspergillus niger. Citric acid is purified by recrystallization the anhydrous form is obtained from a hot concentrated aqueous solution and the monohydrate from a cold concentrated aqueous solution. 

Fruit juices prepared from the pulp contain relatively large amounts of citric acid (Hayakawa, Linko, and Linko, 1999). In most juices citrate is omnipresent, and malic acid is present in high concentrations, with minute concentrations of other organic acids such as lactic acid (Arellano et al., 1997). Lemon juice is often used as an alternative to acidification with citric acid (Valero et al., 2000). 

NACE with indirect detection has been applied to the determination of fatty acids (FAs) and ascorbic acid (AA), respectively. C2-C18 FAs have been separated in less than 12 min using 8-hydroxy-7-iodoquinoline sulfonic acid as chromophores in NACE with indirect absorbance. The dissociation constant (p/linear plot -log[(mu 0/mu) - 1] versus pH, using 20% isopropanol and 40% ACN as the organic modifier in NACE, are all above about two units than those obtained in aqueous solution. NACE with indirect laser-induced fluorescence, using merocyanine 540 MC540) asfluorophores, has been performed for the analysis of AA and its stereoisomer, isoascorbic acid (lAA), and the limits of detection of AA and lAA are 0.30 and 0.17 pM, respectively. This method has been applied to the determination of AA in a lemon juice spiked with lAAasthe internal standard in less than three minutes, and its concentration is 76.7 + 0.4 mM. 

Lemon juice is an electrolyte (an aqueous solution containing citric acid and many other substances). Students can be shown that by inserting two dissimilar electrodes into the lemon, electricity is produced. The voltage output depends on the metals and the concentration of the electolyte. Figure 8.8 shows a battery of two lemons connected in series. 

The acidic nature of a given solution is characterized by its pH, where pH is the negative logarithm of the molar H" concentration (-log (H )). A solution with pH <7 is acid, a solution with pH 7 is neutral, and a solution with pH >7 is basic. For example, the pH of lemon juice is 2, while the pH of lye is about 14. 

With this huge amount of concentrations it is possible to detect frauds like the addition of sugar, exhaustive enzymatic treatment (galacturonic acid), addition of citric acid or lemon juice (e.g. in apple juice), extraction of orange peel (phlorin) or the usage unripe Suits (quinic acid in apple juice). 

A clarified concentrated lemon juice, essentially a solution of citric acid, was described by Georgius, and Retzius also described the preparation of a solution, but crystalline citric acid was first prepared by Scheele, by boiling the lemon juice with chalk, decomposing the precipitated calcium citrate with diluted sulphuric acid, filtering, and evaporating he says a sweetened solution of citric acid makes a good artificial lemonade, and describes some metallic citrates. ... 

Another example of an MCFIA system is shown in Figure 4.6. This MCFIA system was designed to implement an automated titration procedure [36]. The system was applied to samples with a wide range of acid concentration such as vinegar and lemon, orange, pineapple, maracock, and acajou juices. 

Five pubhcations are of special interest because of their wide scope of preserrted material. One has only historical value but other three are of considerable importance. Probably the first information about properties of citric acid and its solutions comes from the above mentioned Robert Warington. He presented to the Chemical Society (London) in 1875 a long paper of 70 pages which was entitled Note on the Chemistry of Tartaric and Citric Acid [15]. Evidently, even today, there is an interest to obtain some glance about analytical procedures then used, properties of imported lemon-juice and other solutions (e g. densities and solubihties), that commercial citric acid was then monohydrate, if prepared from cold water and hemi-hydrate if crystallized from hot water. Warington also observed that concentrated solutions of citric acid when diluted with water suffer considerable contraction with neghgible rise in temperature and that if citric acid is slowly heated to 170 °C, and kept for some time at this temperature, it losses water and aconitic acid is produced. 

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