Paper litmus

Ammonia evolved in the cold (turns moist red litmus-paper blue). Methane may be evolved by stronger and more prolonged heating. 

Colorations or coloured precipitates are frequently given by the reaction of ferric chloride solution with.(i) solutions of neutral salts of acids, (ii) phenols and many of their derivatives, (iii) a few amines. If a free acid is under investigation it must first be neutralised as follows Place about 01 g. of the acid in a boiling-tube and add a slight excess of ammonia solution, i,e., until the solution is just alkaline to litmus-paper. Add a piece of unglazed porcelain and boil until the odour of ammonia is completely removed, and then cool. To the solution so obtained add a few drops of the "neutralised ferric chloride solution. Perform this test with the following acids and note the result ... 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

Place about 0 5 g. of the acid in a boiling-tube and add a slight excess of ammonia solution until just alkaline to litmus-paper. Add a piece of unglazed porcelain and boil until the odour of ammonia is completely removed. (See also p. 332.) To the cold neutral solution add a few drops of neutral FeCl, solution. 

Solubility in water and action of solution on litmus-paper. 

Residual solution. Make just acid with dil. HjSO, and then just alkaline to litmus-paper with Na,COs solution. Extract phenol with ether, distil off latter and identify the residue. Identify the organic acid in the aqueous layer, as in (A) (ii). 

Place 84 g. of iron filings and 340 ml. of water in a 1 - 5 or 2-litre bolt-head flask equipped with a mechanical stirrer. Heat the mixture to boiling, stir mechanically, and add the sodium m-nitrobenzenesulphonate in small portions during 1 hour. After each addition the mixture foams extensively a wet cloth should be applied to the neck of the flask if the mixture tends to froth over the sides. Replace from time to time the water which has evaporated so that the volume is approximately constant. When all the sodium salt has been introduced, boU the mixture for 20 minutes. Place a small drop of the suspension upon filter paper and observe the colour of the spot it should be a pale brown but not deep brown or deep yellow. If it is not appreciably coloured, add anhydrous sodium carbonate cautiously, stirring the mixture, until red litmus paper is turned blue and a test drop upon filter paper is not blackened by sodium sulphide solution. Filter at the pump and wash well with hot water. Concentrate the filtrate to about 200 ml., acidify with concentrated hydrochloric acid to Congo red, and allow to cool. Filter off the metanilic acid and dry upon filter paper. A further small quantity may be obtained by concentrating the mother liquid. The yield is 55 g. 

Add dilute sulphuric acid, with stirring, to the cold alkahne solution until the solution is acid to htmus or Congo red paper and the acid, if a solid, commences to separate as a faint permanent precipitate. Now add dilute sodium carbonate solution until the solution is alkahne (litmus paper) and any precipitate has completely redissolved. Extract the clear solution twice with ether evaporate or distil the ether from the ethereal solution on a water bath CAUTION no flames may be near) and identify the residual phenol as under 1. Remove the dissolved ether from the aqueous solution by boiling, acidify with dilute sulphuric acid and identify the organic acid present (see Sections 111,85 and IV, 175). 

To hydrolyse an ester of a phenol (e.g., phenyl acetate), proceed as above but cool the alkaline reaction mixture and treat it with carbon dioxide until saturated (sohd carbon dioxide may also be used). Whether a solid phenol separates or not, remove it by extraction with ether. Acidify the aqueous bicarbonate solution with dilute sulphuric acid and isolate the acid as detailed for the ester of an alcohol. An alternative method, which is not so time-consuming, may be employed. Cool the alkaline reaction mixture in ice water, and add dilute sulphuric acid with stirring until the solution is acidic to Congo red paper and the acid, if aromatic or otherwise insoluble in the medium, commences to separate as a faint but permanent precipitate. Now add 5 per cent, sodium carbonate solution with vigorous stirring until the solution is alkaline to litmus paper and the precipitate redissolves completely. Remove the phenol by extraction with ether. Acidify the residual aqueous solution and investigate the organic acid as above. 

The reaction is usually complete immediately after the addition of the ethylene chlorohydrin, obviating the necessity for refluxing the mixture. The reaction is complete when the solution is neutral to litmus paper. 

Amberlite IRA-904 Anion exchange resin (Rohm and Haas) [9050-98-0]. Washed with IM HCl, CH3OH (1 10) and then rinsed with distilled water until the washings were neutral to litmus paper. Finally extracted successively for 24h in a Soxhlet apparatus with MeOH, benzene and cyclohexane [Shue and Yan Anal Chem 53 2081 1981]. Strongly basic resin also used for base catalysis [Fieser Fieser Reagents for Org Synth 1511, Wiley 1967]. 

ACID A chemical compound whose aqueous solution turns blue litmus paper red, reacts with and dissolves certain metals to form salts, and reacts with bases to produce salts and water. They are capable of transfeiTing a hydrogen ion (proton) in solution. 

BASE A ehemieal eompound whose aqueous solution turns red litmus paper blue and is eapable of aeeepting or reeeiving a proton from another substanee. They reaet with aeids to form salts and water. 

Examples include hydrochloric acid, nitric acid, and sulphuric acid. These are strong acids which are almost completely dissociated in water. Weak acids, such as hydrogen sulphide, are poorly dissociated producing low concentrations of hydrogen ions. Acids tend to be coiTosive with a sharp, sour taste and turn litmus paper red they give distinctive colour changes with other indicators. Acids dissolve metals such as copper and liberate hydrogen gas. They also react with carbonates to liberate carbon dioxide ... 

The first two are very soluble in water but the last is less so. Weaker bases inelude ammonium hydroxide where X is NH4. In faet every aeid ean generate a base by loss of a proton and the definition now ineludes any eompound eapable of donating eleetron pairs, e.g. amines. Bases turn litmus paper blue and show eharaeteristie effeets on other indieators. They are soluble in water, tarnish in air, and in eoneentrated form are eorrosive to the toueh. Common examples are given in Table 3.5. ... 

Cheek for leaks, e.g. with moist litmus paper or eoneentrated hydroehlorie aeid (whieh forms dense white fumes of ammonium ehloride). 

After the apparatus has been fitted together the caustic soda solution is run in slowly and the flask shaken. The liquid is no more ammonia is evolved be ascertained by testing a drop litmus paper. If the operation is titrated with half-normal sodium methyl orange as indicator. 

Lackmus, m., -farbstoff, m. litmus, -fiechte,/. litmus lichen, archil, -losung, /. litmus solution. -papier, n. litmus paper. 

The aqueous layer should be acidic to litmus paper. If it is basic, indicating that the ammonia was not completely removed from the reaction mixture, more hydrochloric acid should be added until an acidic test is obtained... 

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