Carbonates, qualitative test for

These equations tell us that the reverse process proton transfer from acids to bicarbon ate to form carbon dioxide will be favorable when of the acid exceeds 4 3 X 10 (pK, < 6 4) Among compounds containing carbon hydrogen and oxygen only car boxylic acids are acidic enough to meet this requirement They dissolve m aqueous sodium bicarbonate with the evolution of carbon dioxide This behavior is the basis of a qualitative test for carboxylic acids... 

Oxidation with Benedict s reagent (Section 25 19) Sugars that con tain a free hemiacetal function are called reducing sugars They react with copper(ll) sulfate in a sodium citrate/sodium carbonate buffer (Benedict s reagent) to form a red precipitate of copper(l) oxide Used as a qualitative test for reducing sugars... 

Aldehydes are typically good reducing agents (e.g., the classical qualitative tests for aldehydes involve the production of elemental metallic deposits by reduction). Unfortunately, they increase the carbon content of the treated solution, which poses a serious restriction to their widespread use. 

A qualitative test for carbon monoxide in blood is given on p. 6. 

With ferric salts in solution either of these reagents forms the cherry red ferric thio-cyanate and is the basis of qualitative tests for iron and the use of the thio-cyanate as an indicator in volumetric titrations. Potassium thio-cyanate may be prepared by heating potassium cyanide with sulphur or ammonium sulphide. Ammonium thio-cyanate may be prepared by heating together carbon disulphide and ammonia in the presence of alcohol. 

Newer methods of chemical analysis led to the isolation of the major alkaloids from crude drug preparations. By 1833, aconitine, atropine, codeine, hyoscyamine, morphine, nicotine, and strychnine had been isolated from plants. Color tests for alkaloids were developed between 1861 and 1882 by 1890 quantitative analysis methods became available. Physiological tests for alkaloids, particularly strychnine, first used in 1856, were employed well into the twentieth century. Tests for alcohol, devised by Lieben (iodoform crystal test, 1870) and others, were later perfected for the quantitative analysis of alcohol in body fluids and tissues. Qualitative tests for carbon monoxide in the blood were developed about this time and in 1880, Fodor developed a palladium chloride reduction method to quantitate carbon monoxide in blood. 

Qualitative tests for carbon, hydrogen, nitrogen, sulphur, chlorine, bromine, iodine, 72. 

When an alkene (or any other unsaturated organic compound) is burned in air, a yellow, luminous flame is observed, and considerable soot (unbumed carbon) is formed. This reaction provides a qualitative test for unsaturation. Saturated hydrocarbons bum in air without forming significant amounts of soot. 

If, on boiling with ammonia, virtually no colour migrates into the liquor, a mordanted or premetallized dye is probably present. This is confirmed by testing for the presence appropriate metallic ions. To do this the material must be ashed, and the method recommended by Clayton is to heat about 1 sq in., if possible, in a platinum or silica dish until charring has taken place. The dish is then cooled and the residue is covered with a hot saturated solution of sodium nitrate, the water is evaporated, and heating is continued until all the carbon has burned away. The ash is extracted with water or dissolved with the aid of a little hydrochloric acid, and the usual qualitative tests for metallic ions are applied. 

The tests which have been described are used to detect unsaturated compounds. It is difficult to prove that a compound under study is a hydrocarbon. To do this a qualitative test for elements other than carbon, hydrogen, and oxygen must be made. If such elements are shown to be absent, the substance must be tested for the characteristic groups which con-... 

The visual proof is the formation of a white precipitate of CaC03. Why would a water solution of NaOH be unsuitable to qualitatively test for carbon dioxide ... 

The metal is oxidized by hot air and also reacts with carbon, phosphorus, sulphur, and dilute mineral acids. Cobalt salts, usual oxidation states II and III, are used to give a brilliant blue colour in glass, tiles, and pottery. Anhydrous cobalt(II) chloride paper is used as a qualitative test for water and as a heat-sensitive ink. Small amounts of cobalt salts are essential in a balanced diet for mammals (seeESSENTiAL element). Artificially produced cobalt-60 is an important radioactive tracer and cancer-treatment agent. The element was discovered by Georg Brandt (1694-1768) in 1737. 

The reaction of bromine with an alkene is a particularly useful qualitative test for the presence of a carbon-carbon double bond. If we dissolve bromine in dichloromethane, the solution turns red. Both alkenes and dibromoalkanes are colorless. If we now mix a few drops of the bromine solution with an alkene, a dibromoalkane is formed, and the solution becomes colorless. 

The special problem of lactic acid determination in sweet wines was studied by Berg and Schulze (1931) using barium carbonate for removal of sugars. The results were only fair. A qualitative test for lactic acid was developed by Widmer (1931). He neutralized the volatile acid distillate with barium hydroxide and added alcohol under specific conditions. A small amount of precipitate which settled slowly indicated lactic. 

The addition of reagents X-Y to carbon-carbon ir-bonds may also proceed via a concerted mechanism in which each new a-bond is formed simultaneously on the same face of the ir-bond. The stereochemistry of such reactions is necessarily syn. For example, the reaction of potassium permanganate, which is purple, with an alkene such as cyclohexene proceeds via si/H-addition of permanganate ion across the ir-bond to give 39, which is colorless. Subsequent decomposition of 39 gives a ds-l,2-diol and manganese dioxide, the brown precipitate that is observed as the other product of the reaction (Eq. 10.19). This decoloration of potassium permanganate by alkenes forms the basis of the Baeyer qualitative test for the presence of carbon-carbon ir-bonds (Sec. 25.8B). 

Two common types of unsaturated compounds are alkenes and alkynes, characterized by the carbon-carbon double and triple bonds, respectively, as the functional group. The two common qualitative tests for unsaturation are the reaction of the compounds with bromine in dichloromethane and with potassium permanganate. In both cases, a positive test is denoted by decoloration of the reagent. There are no simple, direct ways to prepare solid derivatives of unsaturated aliphatic compounds having no other functional groups. 

Test for a Carboxylic Acid. As illustrated in the above reaction, when a carboxylic acid comes in contad with a solution containing bicarbonate ion, carbon dioxide is generated. Once saturation of the solution by carbon dioxide occurs, bubbles of carbon dioxide gas are observed to form in the Uquid phase. This effervescence may be used as a qualitative test for the presence of the carboxylic acid functional group in an unknown substance. 

Students usually identify the existence of anions such as carbonate, iodide and sul-fate(VI) by adding a barium/silver(I)/lead(II) solution to the unknown, followed by a dilute acid or vice-versa in qualitative analysis practical work sessions and examinations. Mat r students had difficulty understanding the roles of the bar-ium/silver(I)/lead(II) solution and the dilute acid in the tests for anions. For example, 20% believed that the addition of aqueous barium nitrate(V) followed by dilute nitric(V) acid was to test for sulfate(VI) only. Another 25% believed that to test for a carbonate, acid had to be added directly to the unknown sample, while 20% believed that the addition of barium nitrate(V) invalidated the test for carbonates. When the students were asked the purpose of adding dilute nitric(V) acid following die addition of silver nitrate(V) solution (in one question) and lead(II) nitrate(V in another question) to the unknown solutions, 22% and 35%, respectively, indicated... 

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