How to use: Drag the slider to the left to add acid, or to the
right to add alkali. The beaker shows what universal indicator would look
like in that solution. The scale on the right is the pH scale.
Notice the [H⁺] readout — every step of 1 on the pH scale changes
the hydrogen ion concentration by a factor of ten.
Notice: pH 7 is neutral. Lower pH = more H⁺ ions = more acidic. Higher pH = fewer H⁺ ions (more OH⁻) = more alkaline. Each step of 1 on the pH scale is a ten-fold change in H⁺ concentration. pH 3 has 10 000× more H⁺ than pH 7.