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4.2.3 A Applicati ION

The document describes the Karl Fischer reaction, which uses a coulometric titration to determine the amount of water in a sample. It can detect water concentrations down to milligrams per liter. The reaction involves converting iodine to hydrogen iodide in the presence of water, sulfur dioxide, and a solvent like methanol or ethylene glycol. Reagents must be anhydrous. The amount of water is determined through back or direct titration. Back titration involves adding excess reagent then titrating with a standard solution, while direct titration adds just enough reagent. Coulometry can also determine film thickness by measuring the electricity needed to dissolve a defined area of a metallic coating.

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81 views1 page

4.2.3 A Applicati ION

The document describes the Karl Fischer reaction, which uses a coulometric titration to determine the amount of water in a sample. It can detect water concentrations down to milligrams per liter. The reaction involves converting iodine to hydrogen iodide in the presence of water, sulfur dioxide, and a solvent like methanol or ethylene glycol. Reagents must be anhydrous. The amount of water is determined through back or direct titration. Back titration involves adding excess reagent then titrating with a standard solution, while direct titration adds just enough reagent. Coulometry can also determine film thickness by measuring the electricity needed to dissolve a defined area of a metallic coating.

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vibumonvarghese
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© Attribution Non-Commercial (BY-NC)
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(in amper and the duration of the current ( res) (seconds) ca be used to determine the moles of an o t f the unkno

species in solution. When the v own volume of the solution is known, then e n the molar of the un rity nknown spec can be d cies determined.

APPLICATI ION 4.2.3 A 4.2.3.1 KARL FISCHER REACTIO L R ON

The K Fischer reaction uses a coulometric titration to determin the amoun Karl r ne nt of water in a sample. It can deter rmine concen ntrations of w water on the order of mi e illigrams per r liter. It is used to find the amount of water in substances such as butt sugar, ch s d t n ter, heese, paper, , and petro oleum. The re eaction involves convert ting solid iod into hyd dine drogen iodid in the de presence of sulfur dio oxide and w water. Methan is most o nol often used as the solvent, but ethylen s ne glycol an diethylene glycol also work. Pyrid is often used to prev the buil nd e o dine n vent ldup of sulfuri acid, altho ic ough the use of imidazol and dietha e le anolamine fo this role ar becoming or re g more com mmon. All re eagents must be anhydro for the an ous nalysis to be quantitative The e e. balanced chemical eq d quation, usin methanol and pyridine, is: ng

In this reaction, a single molecule of wate reacts with a molecule of iodine. s er h e Since this technique is used to de etermine the water conte of sample atmosphe humidity ent es, eric y could alte the results Therefore, the system is usually is er s. solated with drying tubes or placed in s an inert g container In addition the solven will undou gas r. n, nt ubtedly have some water in it so the e r solvents water conte must be measured to compensate for this inaccuracy. s ent m e To determine the amount of w water in the sample, anal s lysis must fir be rst performe using eith back or direct titration In the dire method, j enough of the ed her d n. ect just reagents will be adde to comple ed etely use up a of the wa all ater. At this p point in the t titration, the e current ap pproaches zero. It is then possible to relate the amount of re n o a eagents used to the amount o water in th system vi stoichiome of he ia etry. The bac ck-titration m method is sim milar, but involves the addition of an exces of the reag n ss gent. This ex xcess is then consumed by adding a b known am mount of a standard solu s ution with kn nown water content. The result reflects the water e r content o the sample and the sta of e andard soluti ion. Since th amount of water in the standard he f e solution is known, th difference reflects the water conte of the sam i he e ent mple. 4.2.3.2 DETE ERMINATI ION OF FIL THICK LM KNESS

Coulo ometry can b used in the determinat be e tion of the th hickness of m metallic coatings. This is perf formed by m measuring the quantity of electricity n e f needed to dissolve a wel lldefined a of the co area oating. The f film thickness is prop portional to the constant current , t the molec cular weight t of the metal, the de m ensity of th metal, and the surface area : he d e

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