Solubility of iodine in water

The solubility of iodine in water has not been so closely investigated as that of chlorine or bromine,4 and the determinations are not in close agreement. H. Hartley and N. P. Campbell found that water dissolves... 

Pour water into two test tubes and lower one crystal of the iodine prepared in the preceding experiments into each of them. Vigorously shake the contents of the tubes. What is the solubility of iodine in water Write the equation of the reaction of iodine with water. 

Potassium iodide also enhances the solubility of iodine in water. 

Problem 9 At 25°C, the distribution coefficient of iodine between CCl4 and water is 85. If at 25 °C, the solubility of iodine in water is 0.33 g/litre, determine the solubility of iodine in CCI4. 

The solubility of iodine in water is 0.00134 moles per liter. The apparent solubility of iodine in 0.007 molar KI (as determined from the concentration of titratable iodine) is 0.0048 molar. Calculate the apparent solubility of iodine in 0.10 molar KI. 

The solubility of chlorine per 100 cc. of water at 20° is 1.85 g. that of bromine is 3.58 g. and that of iodine 0.28 g. Both chlorine and bromine form crystalline hydrates, C12-8H20 and BrjTOHjO. They are stable only at low temperatures (0-9°). The increased solubility of bromine in potassium bromide solution is ascribed to the formation of KBr if such solutions are saturated with bromine, the vapor pressure of the latter is the same as that of a water solution saturated with bromine. However, the halogen can be removed completely by extraction with carbon disulfide or by a stream of air the KBra must be stable only in the presence of free bromine. The solubility of iodine in water is increased by potassium iodide to 1.4 g. per 100 cc. and in ethanol a 20% solution can be formed. 

So far we have considered the adsorption to be influenced solely by attractive forces to the carbon surface, but often of equal or even greater significance are the forces that solutes can exert on solution status of one another. Potassium iodide increases the solubility of iodine in water and thereby reduces the adsorption of iodine. Conversely, the adsorption of fatty acids is increased when the solubility is reduced by the addition of sodium chloride. The effect on fatty acids is in sharp contrast to that observed with mercuric chloride. The adsorption of mercuric chloride may be diminished 60% when sodium chloride is present this action is ascribed to the formation of a weakly adsorbable complex, Na2HgCI4.28... 

If the iodine reagent is not available as a stock solution, prepare it by dissolving 1 g of iodine in a solution of 2 g of potassium iodide in 8 mL of water. The potassium iodide is added to increase the solubility of iodine in water by formation of potassium triiodide, KI3 (Eg. 25.22). 

At a given temperature the solubility of iodine in water is 0.35 g dm. What will be its solubility in CCl (Distribution ratio of iodine in CCI4 and water is 88). 

Expression (2) applies to a solubility equilibrium, provided we write the chemical reaction to show the important molecular species present. In Section 10-1 we considered the solubility of iodine in alcohol. Since iodine dissolves to give a solution containing molecules of iodine, the concentration of iodine itself fixed the solubility. The situation is quite different for substances that dissolve to form ions. When silver chloride dissolves in water, no molecules of silver chloride, AgCl, seem to be present. Instead, silver ions, Ag+, and chloride ions, Cl-, are found in the solution. The concentrations of these species, Ag+ and Cl-, are the ones which fix the equilibrium solubility. The counterpart of equation (7) will be... 

Chlorine and bromine are fairly soluble in water iodine has a low solubility. Early determinations of the solubility of chlorine in water were made by J. L. Gay Lussac1 in 1839, by J. Pelouze in 1843, and by F. Sohonfeld in 1855. They noticed a maximum in the solubility curve in the vicinity of 10°, and at 100° the solubility is nil. Later determinations have been made by H. W. B. Roozeboom in 1885, and by L. W. Winkler in 1907. At temp, below 9 6°, chlorine forms a crystalline hydrate, C12.8H20 and this corresponds with the maximum in the solubility curve. The solubility curves of the gases chlorine and bromine 2 are indicated in Table III. 

The solubility of the halogens in organic solvents.—L. Bruner33 has measured the solubility of iodine in mixtures of ethyl alcohol and water at 15° ... 

The tinctura iodi of the British Pharmacopoeia is a soln. of half an ounce of iodine, and a quarter of an ounce of potassium iodide in a pint of rectified spirit. P. Wantig found the mol. ht. of soln. —1 941 Cals., and S. U. Pickering —1 714 per 880 mol. of ethyl alcohol. C. Lowig found that alcoholic tincture of bromine is slowly decomposed in darkness, rapidly in light. Alcoholic soln. of iodine, according to H. E. Barnard, are stable in light and in darkness, but according to J. M. Eder they decompose 1000 times more slowly than chlorine water under similar conditions T. Budde has shown that hydriodic acid, acetic ester, and aldehyde are formed, and the electrical conductivity of the soln. increases. J. H. Mathews and E. H. Archibald and W. A. Patrick found a freshly prepared AT-soln. to have an electrical conductivity of 2 4 XlO-6 reciprocal ohms and a sat. soln., 1 61 X10 4 reciprocal ohms at 25°. The decomposition is accelerated by the presence of platinum. The heat of soln. decreases with concentration from —7 92 to —7 42 cals, respectively for dilute and sat. soln. in methyl alcohol, and likewise from —4 88 to —5 22 cals, for similar soln. in ethyl alcohol. The solubility of iodine in aq. soln. of propyl alcohol is not very different from that in ethyl alcohol. 

I. 45 THE DISTRIBUTION OR PARTITION LAW It is a well-known fact that certain substances are more soluble in some solvents than in others. Thus iodine is very much more soluble in carbon disulphide, chloroform, or carbon tetrachloride than it is in water. Furthermore, when certain liquids such as carbon disulphide and water, and also ether and water, are shaken together in a vessel and the mixture allowed to stand, the two liquids separate out into two layers. Such liquids are said to be immiscible (carbon disulphide and water) or partially miscible (ether and water), according as to whether they are almost insoluble or partially soluble in one another. If iodine is shaken with a mixture of carbon disulphide and water and then allowed to settle, the iodine will be found to be distributed between the two solvents. A state of equilibrium exists between the solution of iodine in carbon disulphide and the solution of iodine in water. It has been found that when the amount of iodine is varied, the ratio of the concentrations is constant at any given temperature. That is ... 

Morrison P, Pine J (1955) Radiogenic origin of the helium isotopes in rock. Ann NY Acad Sci 62 69-92 Musselwhite DS, Drake MJ (2000) Early outgassing of Mars implications from experimentally determined solubility of iodine in silicate magmas. Icaras 148 160-175 Musselwhite DS, Drake MJ, Swindle TD (1991) Early outgassing of Mars supported by differential water solubility of iodine and xenon. Nature 352 697-699... 

The chemical drive is strongly negative so the process can only run backward spontaneously. Solid iodine would precipitate from a solution with a concentration of 1 kmol m. However, this does not mean that iodine is not at all soluble in water. Increasing the dilution decreases the potential of iodine in water so that the drive can become positive when the dilution is high enough. More about this in Chap. 6. 

Iodine forms the most extensive group of polyhalide anions, with triiodide, I3, being the best-known example. The formation of this anion is responsible for the increased solubility of I2 in water on addition of potassium iodide (KI). Triiodide is used extensively in analytical chem-isfly, many analytical procedures being based on the release or uptake of iodine and its subsequent titration with sodium thiosulfate (iodometry). The largest polyhalide anion known, Ijg, consists of an alternate arrangement of triiodide anions and neutral iodine molecules. 

Bromine. In this experiment with bromine the absorption equilibrium between the solid phase and the liquid phase was attained after 1 hr for chitin but after 5 days for H-alg. Although the limited solubility of bromine in water precludes measurements at high concentrations, as shown in Figure 6, these saccharides absorb bromine (A) and bead form Ca-alg. has a high binding ratio corresponding to the concentration of bromine (B). Being different from chitin, chitosan absorbs bromine in water up to 1.12 molar bromine per two hexosaminyl residues [14] and neither bromine nor iodine is adsorbed on A-acetylchitosan [14]. The latter conflicts with our results for the chitin-iodine and chitin-bromide adducts. 

Starch consists of two main components amylose (insoluble in cold water) and amylopectin (soluble in cold water). Amylose, which accounts for about 20 per cent by weight of starch, has an average molecular weight of over 10. It is a polymer of glucopyranose units linked together through a l,4 -linkages in a linear chain. Hydrolysis of amylose produces maltose. Amylose and iodine form a colour complex, which is blue/black. This is the colour reaction of iodine in starch, a confirmatory test for the presence of starch. 

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