Editing Fehling's solution (section)

==Laboratory preparation==
Fehling's solution is prepared by combining two separate solutions: Fehling's A, which is a deep blue aqueous solution of [[copper(II) sulfate]], and Fehling's B, which is a colorless solution of aqueous [[potassium sodium tartrate]] (also known as [[Rochelle salt]]) made strongly alkaline with [[sodium hydroxide]]. These two solutions, stable separately, are combined when needed for the test because the copper(II) complex formed by their combination is not stable: it slowly decomposes into copper hydroxide in the alkaline conditions. The active [[reagent]] is a tartrate complex of Cu<sup>2+</sup>, which serves as an [[oxidizing agent]]. The tartrate serves as a ligand. However, the coordination chemistry is complex and various species with different metal to ligand ratio have been determined.<ref name="Hörner">T. G. Hörner, P. Klüfers: ''The Species of Fehling's Solution.'' In: ''[[Eur. J. Inorg. Chem.]]'' 2016, S. 1798–1807, [[doi:10.1002/ejic.201600168]].</ref><ref name="Fangfang">Fangfang Jian, Pusu Zhao, Qingxiang Wang: ''Synthesis and crystal structure of a novel tartrate copper(II) two-dimensional coordination polymer: {[Cu<sub>2</sub>(C<sub>4</sub>H<sub>4</sub>O<sub>6</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·4H<sub>2</sub>O}<sub>∞</sub>.'' In: ''J. Coord. Chem.'' 58, 2005, S. 1133–1138, [[doi:10.1080/00958970500148446]].</ref><ref name="Prout">C. K. Prout, J. R. Carruthers, F. J. C. Rossotti: ''Structure and stability of carboxylate complexes. Part VII. Crystal and molecular structures of copper(II)meso-tartrate trihydrate and copper(II)d-tartrate trihydrate.'' In: ''[[J. Chem. Soc.]]'' A, Inorg. Phys. Theo., 1971, S. 3336–3342, [[doi:10.1039/J19710003336]].</ref><ref name="Kotru">I. Quasim, A. Firdous, B. Want, S. K. Khosa, P. . Kotru: ''Single crystal growth and characterization of pure and sodium-modified copper tartrate.'' In: ''J. Cryst. Growth.'' 310, 2008, S. 5357–5363, [[doi:10.1016/j.jcrysgro.2008.09.021]].</ref><ref name="Jespersen">N. D. Jespersen: ''Novel Copper-Tartrate Coordination Compounds.'' In: ''Anal. Let.'' 5, 1972, S. 497–508.</ref>

Other methods of preparing comparable cupric-ion test-reagent solutions were developed at about the same time as Fehling's. These include the Viollette solution (eponymous for {{ill|Charles Cléophile Viollette|fr}} (1823–1894)) and the Soxhlet solution (eponymous for [[Franz Ritter von Soxhlet]] (1848–1926)), both containing tartrate, and Soldaïni's solution (eponymous for Arturo Soldaïni),<ref>Arturo Soldaïni (1876) Nuovo reattivo pel glucoso.Gazzetta della Chimica Italiana 6 322-324. available at https://catalog.hathitrust.org/Record/000679312/Home</ref> which instead contains carbonate.<ref>{{cite book |title= Handbook for Cane-sugar Manufacturers and Their Chemists |publisher= Wiley |year= 1898<!-- front-matter in the Google-books have both 1889 and 1898, and it's the third edition; late-1890s is more self-consistent; maybe 1889 is first edition? --> |first= Guilford L. |last= Spencer |pages= 62–63 |edition= third |url= https://books.google.com/books?id=_6w5AQAAIAAJ }}</ref>  [[Barfoed's test]] is also related and similar to Fehling's test (eponymous for [[Christen Thomsen Barfoed]] (1815–1889)).