Examples citric acid titration

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. 

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... 

Sources of error can be introduced in each conversion from volume to moles and back to weight, although for simple examples such as the one above it does not really matter which method of calculation is employed as long as the correct answer for the purity of citric acid is obtained. However, for more complicated calculations, involving the use of back and blank titrations, this author believes that factors and equivalents simplify volumetric analysis and they will be used for that reason (rather than any reason of dogma) in the remainder of this book. 

How far apart must successive pK values be in order to have clearly distinguishable endpoints for titration curves of polyprotic acids Consider as examples H3PO4 and citric acid. What about equivalence points at very high or low pH How easy are they to locate ... 

At first insight, the case of a polyacid can be assimilated to that of a mixture of several acids whose concentrations would be identical. With this reasoning in mind, the previous experimental rules can be applied to this case. Two striking examples are provided by the titrations of phosphoric acid and citric acid. 

Considering increasing use of non-aqueous or water-organic solvent media in analytical chemistry (for example in potentiometric titrations and in the high-performance liquid chromatography), dissociation constants of citric acid in few such systems were also determined. Evidently, they are less abundant than those in water. These dissociation constants are actually the concentration quotients, because activity coefficients and aetivities of water were always ignored. 

The major acids of must are L-tartaric and L-malic acids. Succinic, citric and some other acids are minor constituents. In a good vintage, tartaric acid is 65-70% of the titratable acidity, but in years when unripe grapes are fermented, its content is only 35-40% and malic acid predominates. The good vintage year of 1911, for example, yielded grapes with 3.1 g/1 malic acid and 6.4 g/1 tartaric acid in the inferior vintage year of 1912, on the other hand, malic acid was 10.7 g/1 and tartaric acid 6.0 g/1. 

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