Potassium bromide: formation

Calculate the standard enthalpy of formation. AH potassium bromide. 

Lead is not generally attacked rapidly by salt solutions (especially the salts of the acids to which it is resistant). The action of nitrates and salts such as potassium and sodium chloride may be rapid. In potassium chloride the corrosion rate increases with concentration to a maximum in 0.05m solution, decreases with a higher concentration, and increases again in 2m solution. Only loosely adherent deposits are formed. In potassium bromide adherent deposits are formed, and the corrosion rate increases with concentration. The attack in potassium iodide is slow in concentrations up to 0.1m but in concentrated solutions rapid attack occurs, probably owing to the formation of soluble KPblj. In dilute potassium nitrate solutions (0.001 m and below) the corrosion product is yellow and is probably a mixture of Pb(OH)2 and PbO, which is poorly adherent. At higher concentrations the corrosion product is more adherent and corrosion is somewhat reduced Details of the corrosion behaviour of lead in various solutions of salts are given in Figure 4.16. 

J.5 Select an acid and a base for a neutralization reaction that results in the formation of (a) potassium bromide (b) zinc nitrite (c) calcium cyanide, Ca(CN)2 (d) potassium phosphate. Write the balanced equation for each reaction. 

Pure potassium bromide, KBr, which adopts the sodium chloride structure, has the fraction of empty cation sites due to Schottky defects, ncv/Nc, equal to 9.159xl0-21 at 20°C. (a) Estimate the enthalpy of formation of a Schottky defect, Ahs. (b) Calculate the number of anion vacancies per cubic meter of KBr at 730°C (just below the melting point of KBr). The unit cell of KBr is cubic with edge length a = 0.6600 nm and contains four formula units of KBr. 

The excess of potassium bromide allows the required reaction temperature to be achieved moreover, a high concentration of bromide ion suppresses the formation of the corresponding a-hydroxy acid. 

Addition of a solution of bromine and potassium bromide to a solution of the carboxylate salt E results in the precipitation of a neutral compund having the formula CnH13Br03. Various spectroscopic data show that the compound is non-aromatic. Suggest a structure and discuss the significance of the formation of this product. 

Potassium bromide also can be prepared by treating iron turnings with a 35 wt% aqueous solution of bromine. The product ferrosoferric bromide is boded in potassium carbonate solution containing a slight excess of 15% potassium carbonate (Dancy, W.B. 1980. Potassium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 3 i ed. p. 963. New York Wiley Interscience). The method does not involve bromate formation. The second step of the process may be represented in the foUowing reaction ... 

Uracils and related pyrimidines undergo oxidative addition to the 5,6-double bond, and the reaction with a number of oxidants to form 5,6-epoxides and 5,6-diols was discussed in CHEC-II(1996) <1996CHEC-II(6)93>. Oxidative halogenation can also occur <1996SC3583, 1998NN1125>, as shown by the formation of 5-bromo-5,6-dihydro-6-methoxyuracil 100 from uracil 99 by treatment with a mixture of potassium bromate and potassium bromide in the presence of Dowex ion-exchange resin in methanol <1996SC3583>. 

The increase in the solubility of bromine in soln. of ammonium salts is very marked, as is also the case with the alkali chlorides. The case with the alkali bromides is specially interesting. The solubilities by F. P. Worley are indicated in Table IX. The marked increase in the solubility of bromine in soln. of potassium bromide was attributed by M. Roloff to the formation of molecules of KBr3. He shook up a soln. of bromine in carbon disulphide with water and with an aq. soln. of potassium biomide, and measured the concentration of the bromine in the two layers. M. Wildermann has shown that the density of bromine vapour over a soln. of potassium bromide sat. with bromine is the same as over water sat. with bromine, indicating that the cone, of the free bromine in all the aq. soln. is the same, and any excess in the presence of potassium bromide must be united with the potassium bromide. All the bromine dissolved by a soln. of potassium bromide can be removed... 

A soln. of twenty-two grains of iodine and thirty-three grains of iodide of potassium, in one ounce of distilled water forms the liquor iodi of the British Pharmacopoeia. The effects produced by the ammonium salts are attributed to their hydrolysis into ammonium hydroxide, and the consequent formation of ammonium iodide or polyiodide. The effects produced by soln. of the halide salts are doubtless due to the formation of poly iodides as in the analogous case with bromine and potassium bromide. A. A. Jakowkin allowed carbon disulphide to remain in contact with aq. soln. of iodine and potassium iodide until equilibrium was attained and... 

J. Clicm. Soe. 77, ft48 (tqoo). Pickles recommends preparing hydrobromic acid from potassium bromide and sulfuric acid in the presence of a little stannous Hall to prevent the formation of traces of bromine. Clicm. News, 111), Kg (igig). 

Senti and Witnauer1 have provided the only information yet available on the stoichiometry of formation of polysaccharide adducts. Their studies of addition compounds of amylose in aqueous ethanolic media showed that the combining ratio of D-glucose residue to salt is a function of salt concentration, and that the minimum ratios are approached as the salt concentration is increased. Beyond a certain concentration of salt, the ratio becomes almost constant. The anion plays an important role in determining the magnitude of the minimum ratio for an amylose adduct. Potassium bromide and potassium iodide give adducts of minimum ratio 2 1, whereas potassium acetate and potassium propionate give 1 1 adducts. A study of the composition of the potassium acetate adduct as a function of salt concentration indicated that two, relatively stable adducts are formed, the 1 1 and the 2 1. 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

Add 120 g. of powdered potassium bromide to 200 ml. of water. Place the container in cold water, and slowly add 90 ml. of cone, sulfuric acid (1.7 mols). The temperature should not go appreciably above 75°C. otherwise a small amount of free bromine may be formed. However, the formation of a small amount of bromine is not particularly serious, since it will come over with the distillate boiling between 100 to 115°C. Cool the solution to room temperature, and remove the potassium acid sulfate by filtering through a hardened filter paper in a Buchner funnel. Place the filtrate in a 500-ml. distilling flask connected to a water condenser fitted with an adapter, and heat over a wire gauze. If the presence of 0.01 to 0.015 per cent of sulfate ion is not objectionable, reserve the distillate that starts to come over 1° below the temperature of the constant-boiling mixture. The distillation should be stopped when the temperature drops. The specific gravity of the solu-... 

Cinnamic Acid.—Cinnamic acid, investigated by Brester,5 showed a similar behavior in the electrolysis of both the free acid and the neutral solutions of its salts. Lob 6 has reported an accidental observation on the formation of bromstyrene by electrolysis of cinnamic acid in the presence of potassium bromide. 

In a similar manner potassium bromide yields bromine and potassium hydroxide, but the further formation of hypobronute and bromate is less rapid than the analogous reaction with potassium iodide.4... 

The heat of formation of potassium bromide from the elements is given as 95-3 Cal.8 and 95-6 Cal.9 At 20° C. 100 grams of water dissolve 65 grams of the bromide 10 and at 25° C. 100 grams of ethyl alcohol dissolve 0-142 gram.11... 

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