What is solvent leveling? How can we distinguish between two strongly acidic solutions? (This is a challenging question and is included for interest only)

Solvent levelling refers to the effect of the solvent on the properties of acids and bases. The apparent acidity of a solution is limited, or levelled, by the basicity of the solvent it is in. A very strong acid in water will result in 100% protonation of the water molecules. However, another strongly acidic solution will have the same effect, so how do we know which is more acidic? In order to distinguish between these two, we gradually increase the acidity of the solutions which the acids are tested with. Acids want to donate their protons (Bronsted-Lowry) but in the presence of a much stronger acid, they are forced to accept the proton. The stronger acid will protonate a greater proportion of the acidic solution hence this method allows for the relative acidity of very strong acids to be discovered. This method can be used to distinguish between strong bases, weak acids and weak bases by altering the experimental setup.