Adsorption of ioidide ions and nucleation of freshly prepared silver iodide sols

Abstract

The plots „amount I⁻ adsorbed against pI” on freshly precipitated AgI, mol per mol, are linear. At pI=8 and at pI_limit=9.4−9.1 abrupt changes of the slopes can be observed. The slopes of the plots, i.e. the adsorption capacities are proportional to the logarithm of the starting I⁻ concentration and have common zero points of adsorption. The initial I⁻ concentration determines the number of primary particles formed and the number of I⁻ adsorbed per primary particle, i.e. at the starting I⁻ concentration the number of I⁻ adsorbed is maximal and at the Ag⁺ concentration at which the isoelectric coagulation sets in the number of I⁻ adsorbed is minimal. The slope of the plots is explained as being proportional to the difference between the maximal and minimal number of I⁻ adsorbed and to the number of primary particles. The slopes of the plots are the higher the lower is the sol concentration and they are the lower the longer were the times elapsed between the precipitation and the measurement. The presence of cations of various valencies in a concentration higher than the critical one for coagulation cause the minimal adsorption capacity. The increase of the cation valency for 1 causes a shift to lower values of the critical concentration which shift is practically equal for the Na⁺-Ba²⁺ and Ba²-La³⁺ pairs.

Contribution No. 169 of the Laboratory of Physical Chemistry.

Results taken in part from the M. Sc. thesis by S. Musić.