What chemical reaction takes place when you add universal indicator to an acid?
we know that all acids are classified by having the H+ ion and so if you are testing for a acid it must then be this ion which reacts. Therefore this means that the H+ ion must react in such a way with the indicater and so because whichever chemical the indicater is gains hydrogen, this can be thought of a hydrogenation reaction or a gain of hydrogen is a reduction reaction. The acid must then lose the hydrogen and so that is oxidised.