The gastric mucus layer is widely recognized to serve a protective function in the human stomach, shielding the epithelium and the gastric mucosa from the extremely low pH and digestive enzymes present in the stomach lumen. How this gel layer and the extreme pH gradient across it are maintained is not fully understood. Mucus secretion and swelling at the stomach wall are balanced by enzymatic degradation of the gel network at the lumen. All of these processes, as well as the rheology of the mucus itself are mediated by local pH, which is non-uniform throughout the layer. Here, we present a model of gastric mucus based on a two-phase gel framework, combined with a Nernst-Planck treatment of ionic diffusion. Ionic binding and unbinding with the gel phase are also considered. The model allows us to directly address the kinetics of ion mediated mucus swelling immediately after secretion.