  We study charge regulation of colloidal particles inside aqueous electrolyte
solutions. To stabilize colloidal suspension against precipitation, colloidal
particles are synthesized with either acidic or basic groups on their surface.
In contact with water these surface groups undergo proton transfer reaction,
resulting in colloidal surface charge. The charge is determined by the
condition of local chemical equilibrium between hydronium ions inside the
solution and at the colloidal surface. We use a model of Baxter sticky spheres
to explicitly calculate the equilibrium dissociation constants and to construct
a theory which is able to quantitatively predict the effective charge of
colloidal particles with either acidic or basic surface groups. The predictions
of the theory for the model are found to be in excellent agreement with the
results of Monte Carlo simulations. The theory is further extended to treat
colloidal particles with a mixture of both acidic and basic surface groups.
