Which chemical species in solution are acid-base indicators sensitive to?
As it explains on p 343 of the Nuffield students book, an acid-base indicator is itself a weak acid whose molecules and anions impart different colours to a solution. The colour change is produced by shifting the equilibrium (the first equation on p 363 is the relevant one) from one side to the other. If the hydrogen ion concentration is high, the equilibrium shifts to the left and you get the colour due to the indicator molecules. If the hydrogen ion concentration is lowered, e.g. by adding a base such as hydroxide ions, the equilibrium shifts to the right and you get the colour due to the anions of the indicator. The literal answer to your question, therefore, is that indicators are sensitive only to hydrogen ion concentration but this in turn, is of course affected by anything which can change that concentration. Ulex Risk assessment Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the r
