68 Gooch and Heath — Iodometric Determination of Copper 



method and containing 0*0020 grm. to l cm3 , were drawn from 

 a burette and treated with potassium iodide in solution. In 

 some of the experiments the iodine set free was titrated with- 

 out previous dilution, while in others the mixture was diluted 

 previous to the titration. The volumes at precipitation and at 

 the end of the titration are noted. In Series A is shown the 

 effect of twice the amount of potassium iodide theoretically 

 required, at volumes varjdng from 30 cm3 to 80 c,n3 at precipitation 

 and from 36 cm3 to S6 om3 at the end of the titration. 



In the experiments of Series B the effect of increasing the 

 amount of potassium iodide under conditions otherwise similar 

 is studied. In Series C is shown the effect of large dilution of 

 the solution containing the amount of potassium iodide used in 

 the experiments of Series A. 







Table I. 









'fects of Volume of 



Solution and Concentration of 

 Iodide. 



Potassium 





Volume 



KI 



used 



Copper 



equivalent 



to I found 



by Na 2 S,0 3 





Copper 



taken 



as CuSO-4 



At 

 precip- 

 itation 



At end 

 of titra- 

 tion 



Error in 



terms 

 of copper 



grm. 



cm 3 



cm 3 



grm. 

 A 



grm. 



grm. 



0-0400 



30 



36 



•4 



0-0391 



— 0-0009 



0-0400 



40 



46 



•4 



0*0387 



— 0-0013 



0-0400 



50 



06 



•4 



0-0388 



— 0-0012 



0-0400 



60 



66 



•4 



0-0391 



— 0-0009 



0-0400 



80 



86 



•4 



00391 



— 0-0009* 



0-0400 



40 



46 



B 



0-8 



0-0400 



o-oooo 



0-0400 



30 



36 



8-0 



0-0399 



— o-oooif 



0-0600 



45 



54 



13-0 

 C 

 •4 



0-0599 



— o-oooif 



0-0400 



30 



200 



0-0033 



—0-0367; 





0-0400 



30 



300 



•4 



0-0004 



— 0-0396; 





0-0400 



30 



500 



•4 



0-0004 



— 0-0395; 





0-0400 



30 



1000 



•4 



0-0005 



— 0-0395; 





From the results recorded in A it appears that, though the 

 excess of potassium iodide is about 0-2 grm., the amount used 

 being approximately twice that required by the theory, the 

 reaction resulting in the formation ©f cuprous iodide and libera- 

 tion of iodine is not quite complete. On the other hand, the 

 results recorded in B show plainly that at similar dilution the 



* End -point slow in coming. 



f The Cu 2 I 2 was completely dissolved in KI before titrating. 



% Visible precipitation of CU3I2 took place on titrating the free iodine. 



