An aqueous solution is acidic if it contains more H3O- ions than OH- ions. This is because the concentration of H3O- ions determines the acidity or basicity of a solution. In an acidic solution, there is an excess of H3O- ions, which can donate a proton (H+) to other substances, making it corrosive and able to change the color of litmus to red. A high pH value indicates that the solution is basic, not acidic. A bitter taste is not a reliable indicator of acidity, as many substances can have a bitter taste without being acidic.