The movement of chloride ions (Cl⁻) into red blood cells. Carbon dioxide reacts with water to form carbonic acid in the red blood cells (see carbonic anhydrase). The carbonic acid then dissociates into hydrogencarbonate ions (HCO₃⁻) and hydrogen ions (H⁺). The plasma membrane is relatively permeable to negative ions. Therefore the hydrogencarbonate ions diffuse out of the cell into the plasma, leaving the hydrogen ions, which create a net positive charge; this is neutralized by the diffusion of chloride ions from the plasma into the cell.