We consider a model for a two-component solution which consists of a chemically reacting solvent and a chemically inert hard-sphere solute. A directional associative interaction between the solvent molecules promotes the formation of a network. A multi-density associative Ornstein-Zernike equation is solved analytically using the Percus-Yevick approximation. On the basis of the analysis of the osmotic compressibility, an instability curve for different parameters of the model dispersion is constructed. It is shown that concentration and size of colloids affect the formation of associative complexes in a solvent and directs in such a way the location and behavior of the spinodal curves. The effective interaction between colloids is calculated and discussed.