176 



S. E. Moody — Hydrolysis of Salts. 



Art. XVII. — The Hydrolysis of Salts of Iron, Chromium,, 

 Tin, Cobalt, Nickel, and Zinc in the Presence of Iodides 

 and Iodaies; by Seth E. Moody. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxlvi.] 



Iron. 



It has been shown in a former paper* that the action of a 

 mixture of potassium iodide and potassium iodate upon alumi- 

 nium chloride and aluminium sulphate may serve as the basis 

 for the iodometric determination of aluminium. 



Just as salts of aluminium are hydrolyzed in the presence 

 of the iodide-iodate mixture with the liberation of iodine, so 

 are salts of iron. The reaction by which ferric sulphate is 

 hydrolyzed is similar to that for the hydrolysis of aluminium 

 chloride and aluminium sulphate, as already given. 



I\(S0 4 ) 3 + 5KI 4- KI0 3 + 3H 2 = 2Fe(OH) 3 + 3K 2 S0 4 + 6l. 



The hydrolysis of ferrous sulphate is accompanied by oxida- 

 tion of the ferrous hydroxide at the expense of the iodate, as 

 follows 



3FeSO 



) + 5KI + KI0 3 + 3H 2 = 3Fe(OH) 2 + 3K 9 S0 4 + 61 

 6Fe(OH) 2 + KIO, + 3H 2 = 6Fe(OH) 3 + KI. 



The iodine eliminated is an exact measure of such hydrolysis 

 as in the case of aluminium and becomes known by the use of 

 a standard solution of sodium thiosulphate for its titration. 



A solution of ferrous sul- 

 phate was used in the experi- 

 ments performed, made up 

 to about N/10 strength. Its 

 value was obtained with 

 potassium permanganate as 

 shown in Table I. Of 

 this solution portions of 25 cm3 

 were drawn from a burette 

 into a Voit flask, the iodide- 

 iodate mixture added and the 

 whole boiled for 30 minutes 

 in the presence of a current 

 of hydrogen to transfer the 

 iodine to the receiver, a Drexel flask charged with potassium 

 iodide, when it was estimated with a standard solution of 

 sodium thiosulphate. 



Table II shows results of these experiments. ■ 



* This Journal, xx, 1905, p. 181. 



