Ion/Counter ion layers in the colloid precipitate of silver chloride You use a precipitation method to determine [Ag+] in an unknown sample using Cl- ions. Reaction is conducted in presence of HNO3 in excess (relative to Ag+) Which statement is correct concerning the colloid precipitate at the start of the rxn (rxn not yet complete).
A) The ion in Primary Absorption layer is Cl-
B) The Colloid Particle is (-) charge
C) Ag+ is the major ion in Counter-ion Layer
D) Most Cl- ions added are in the precipitate form.

So I think the correct answer is D through process of Elimination and not chemistry knowledge. I know B is incorrect, B/C the precipitate must be AgCl, or possibly AgNO3 since there's Nitric acid here. Both of these are neutrally charged.
I'm pretty sure that Primary absorption layer is the &quot;opposite&quot; of the counter ion layer. So whichever ion goes into the Primary, the opposite ion goes in the counter. Therefore I eliminated A and C, since one cannot be correct without the other being correct as well. (although my first instinct was to put Ag+ in the primary ion layer).
I still have doubts about D. Since the reaction is not complete, and we are adding Cl- to a solution of Ag+, its safe to assume that any Cl- added will react. But HNO3 is a strong acid which dissociates completely, that means there's an excess of NO3- ions floating around. I'm not given any precipitation constants. Can I safely assume Ag+ will bind with Cl- before making AgNO3?
Also could you please confirm or correct my assumptions about Primary/counter-ion layer? I can't find any info it besides vague definitions.
It isn't absolutely clear from the wording, but it seems you're adding $\ce{Cl^{-}}$ to a $\ce{Ag^{+}}$ solution.

As some of the $\ce{Cl^{-}}$ is added, $\ce{Ag^{+}}$ is still in excess in the solution so virtually all of the $\ce{Cl^{-}}$ precipitates. $\ce{Ag^{+}}$ will be the primary adsorbent on the precipitate, and the colloidal particles will have a positive charge.  

Since the colloidal particles have a positive charge, the ion in the counter-ion layer around the particle needs to be negatively charged. There isn't any  $\ce{Cl^{-}}$ in solution so it has to be $\ce{NO3^{-}}$ as the anion. 

Thus the correct answer is (D).