C. Chloride vs Sulfate. We applied the same analysis to anion identity to corroborate whether cation behavior did indeed play the largest role at the interface. While positively charged counterions make up most of the species in the Stern layer under the conditions explored in our experiments (pH 5.8), previous experiments have shown a small number of SiOH + groups present even at neutral pH conditions. In titrations of Na2SO4 and MgSO4, we observe changes in both and Φ " (Fig. ) and χ (Fig. ) indicating that the presence of sulfate anions may have outsize effects on interactions at the interface, where the establish the largest negative potential at ionic strengths < 1mM. Sulfates have been postulated to lead to silica dissolution through salting out effects that become especially pronounced at high temperatures. In spite of silica's overall negative charge at circumneutral pH, we observe a reduction in χ and Φ " with the addition of Na2SO4 which demonstrates that the anion species likely plays a role in the electrical double layer 72 even though the "standard" electrical double layer model (e.g. Gouy-Chapman-Stern theory) predicts Na + should be the predominant surface-bound species. We observe the opposite trend for the 2:2 salt MgSO4 which could indicate that sulfate ions have a notable influence on the magnesium ion coverage. We postulate that these may play a role in the changes in overall structure that facilitate salting out effects (i.e. sulfate-silicic acid structures that form) at higher concentrations. We also note that the Φ " point estimates for chloride and sulfate anions are invariant between each shared cation species at ionic strengths > 1 mM, which may indicate little change to hydration structure in the diffuse layer at higher concentrations.